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The three-phase four-wire voltage source inverter (3P4W VSI) is widely used in applications like uninterrupted power supply (UPS) and bidirectional onboard charger. The increasing power density demand requires higher switching frequency and lower switching loss. To fulfill the conflicting objectives, two-fold methodology is proposed in this paper: 1) SiC/Si hybrid switches (HyS) together with recently reported gate trigger are reported for the first time in the 3P4W VSI; 2) the natural point voltage is controlled to track a sinusoidal voltage with the frequency equal to 3 times of fundamental frequency in order to achieve higher DC-bus voltage utilization rate, and further reduce the switching loss. The traditional PI controller is very hard to achieve desired performance due to both the nonlinearity and the variant reference of the natural point voltage control system. Thereby, the super-twisting sliding mode control (ST-SMC) is proposed in this paper to achieve desired tracking performance and fast dynamic response. The effectiveness and superiority of the system are verified by both simulation and experiment comparison with the existing methods using a 5 kW prototype. • A new trigger circuit proposed recently is used for the first time in a 4 legs inverter. • The relationship of DC-bus voltage and HyS switching loss is derived and testified. • The super-twisting sliding mode control achieves high tracking accuracy in 3P4W inverter. • HyS and suitable controller comprehensively improve the performance of 3P4W inverter. [ABSTRACT FROM AUTHOR]

In this study, a global fast terminal sliding-mode control (GFTSMC), which offers a faster convergence performance than its counterparts is constructed for managing the state variables of the DC–DC buck converters. For the first time in this study, the GFTSMC was designed for power electronics circuits based on hysteresis modulation (HM). The HM technique's variable switching frequency problem is overcome by reusing the GFTSMC structure, which enables the hysteresis band to be changed adaptively, and a fixed switching frequency is obtained. The proposed control scheme uses only one sensor for regulating the output voltage and controlling the switching frequency. Thus, an extremely economical and robust system, which is minimally affected by the negative aspects originating from the sensors, is obtained. Effectiveness of the proposed controller is validated with experimental studies. The experimental results shows that the output voltage and switching frequency are successfully controlled with good dynamic and steady state response. Finally, to validate the experimental feasibility of this paper, a comparison of the proposed method and four existing studies with different control schemes is presented. • A GFTSMC offering a faster convergence time is proposed for the buck converter. • Besides, another GFTSMC is designed to obtain adaptive hysteresis band. • Adaptive hysteresis band resolves variable switching frequency problem. • Adaptive hysteresis band provides fixed switching frequency. • The both controllers provide good dynamic and steady state response. [ABSTRACT FROM AUTHOR]

In this paper, an optimized sliding surface predictive control of a three-phase voltage source inverter is introduced. In power electronics, the model predictive control method (MPC) is broadly used and applied to a wide range of energy conversion systems. However, analyzing the stability of the MPC is not a straightforward task, and Lyapunov-based approaches are used to examine the stability characteristics in most cases. MPC is a nonlinear control technique, and the traditional frequency-domain stability tools cannot be used to examine the closed-loop stability. Therefore, a poor design of the MPC without considering the stability may worsen the system performance. Even the norm choice of the objective function leads to closed-loop instability, for example, ℓ 1 norm is not a sufficient choice to guarantee the global asymptotical stability. Even though ℓ 1 norm offers a low computational burden during the online optimization process, the system may suffer from closed-loop instability. For all these reasons, a stability-guaranteed objective function design procedure is proposed in this paper. The proposed objective function selection process is based on the sliding-mode control theory. The objective function is reformulated as a sliding surface function, and the switching combination that satisfies the sliding mode control stability criteria is selected as an optimum input. The mathematical concepts are experimentally validated, and the results demonstrate the potency of the proposed strategy. • A novel stability guaranteed model predictive control method is presented. • The objective function is reformulated as a sliding surface function. • Steady-state performance is improved in three-phase voltage source inverter applications. • Comprehensive performance analyses are performed. • Theoretical concepts are experimentally validated using a real-hardware. [ABSTRACT FROM AUTHOR]

The most conventional control structure for Voltage Source Converters (VSC) is based on the stationary reference frame dq theory, which may result in varying levels of harmonic content in the AC currents and DC voltage oscillations under unbalanced voltage conditions. In the last two decades, numerous papers have proposed controllers with diverse levels of complexity to address these issues. However, a scientific gap exists in the current state of the art regarding the operational limits of conventional dq control in the face of these undesirable operational conditions. The primary contribution of this paper is a mathematical model capable of calculating the phase and magnitude of non-characteristic elements of AC currents, such as negative sequence and third harmonic components, present during unbalanced conditions. These components depend on the power handled by the VSC, the level of voltage unbalance and the bandwidths of the control loops, where the selection of the latter can either enhance the system performance or lead it towards instability. Thus, based on this model, it is now possible to quantitatively define the safe operating limits of a VSC driven by dq control under unbalanced voltages. The validation and effectiveness of the model are confirmed through real-time simulations and prototype experiments. Finally, the proposed novel framework holds potential utility for both industrial and academic applications. • THD in grid currents and DC voltage oscillations are influenced by controller response times and voltage unbalance. • PLL's influence in the generation of uncharacteristic harmonics can be rejected if the response time is long enough. • DC voltage oscillations varies based on the size of the capacitor but also maintains an exponential behavior determined by the ratio of response times. • The increase in the DC capacitor size has no influence on the reduction of harmonic content in the grid currents. • The appropriate selection of the ratio between the response times of the controllers makes it possible to maintain a safe operational limit of the VSC even under conditions of strong voltage unbalance using a conventional dq controller. [ABSTRACT FROM AUTHOR]

Aiming at the voltage exceeding problem caused by the introduction of Photovoltaic (PV) in Active distribution network (ADN), a comprehensive electrical distance index was established considering active and reactive voltage sensitivity, and the uncertainty of traditional PV probability density function (PDF) was optimized by random simulation method. The electrical distance expectation matrix between nodes was established by discretization of PV output probability distribution characteristics, and the ADN system was partitioned by affinity propagation (AP) algorithm. Taking active power loss as the objective function, the non-convex reactive power optimization control problem is transformed into a convex quadratic programming problem by LinDistFlow equation. An improved alternating direction method of multipliers (ADMM) which adaptively adjusts the penalty parameters is used to convert the finite boundaries of adjacent regions into data. By coordinating on-load tap-changer (OLTC), capacitor banks (CBs), and PV inverters on different time scales, the fast optimal control of global voltage in ADN is realized. The proposed method is tested on IEEE 33-bus and IEEE 123-bus distribution systems. After the optimization control algorithm described in this paper, the system network loss was reduced by 3.88%. Compared with the semi-definite programming relaxation, the calculation speed of LinDistFlow equation is increased by 72.2%. The results fully verify the feasibility and high efficiency of the control strategy described in this paper. • A network partition method based on affinity propagation algorithm considering the photovoltaic uncertainty is proposed. • The traditional probability density function (PDF) of PV was updated by the random simulation method. • LinDistflow equation is used to achieve the conversion of the active power loss minimization model. • The ADMM algorithm with penalty parameter adaptive control is used to realize the distributed control of the ADN system. •.The voltage/var control schemes of OLTC, CBs and PV inverters are presented through multi-time scale scheduling. [ABSTRACT FROM AUTHOR]

Although the optimal power flow (OPF) problem has been extensively studied, solving realistic OPF models that accurately represent the operating behavior of power system components remains challenging. This paper proposes a novel model for the AC OPF problem, aiming to minimize the fuel costs of thermal units while taking into account valve-point loading effects (VPLE), prohibited operation zones (POZ), multiple fuel options (MFO), and operational rules associated with the discrete tap ratios of on-load tap changer (OLTC) transformers and with the discrete shunt susceptances of capacitor/reactor banks. These rules are represented using complementarity constraints. We propose a solution approach that integrates several strategies to address the non-smooth features of the objective function related to VPLE, the disjoint constraints and functions tied to POZ and MFO, the discrete characteristics of the reactive control variables, and the complementarity constraints governing operational rules linked to voltage control devices such as OLTC transformers and capacitor/reactor banks. The resulting optimization problem is designed to be compatible with commercial solver packages. Numerical tests on the IEEE 30, 118, and 300-bus systems aim to examine the cumulative impact of these operational factors on the optimal solution. The solution strategy proposed has demonstrated its effectiveness in solving the proposed OPF problem within reasonable computation times. • This paper proposes a novel model for the AC OPF problem. • The model proposed represents operational rules governing reactive power controls. • Although used in practical, these rules have not been addressed in the literature. • The novel rules are represented using complementarity constraints. • Proposed solution approach integrates strategies to handle imposed characteristics. [ABSTRACT FROM AUTHOR]

A major reason for compromised audio quality with a coil-type loudspeaker is its complex impedance profile, which disturbs the intended algebraic linearity or linear phase behavior between the amplifier input and speaker driving force. Though switch-mode amplifiers are increasingly preferred in such audio systems owing to their superior energy efficiency, their inherent non-linearity and finite internal impedance further degrade audio reproduction. This paper investigates the effect of stated impedance on the loudspeaker driving current, hence on the loudspeaker driving force, and proposes a Hybrid controller-amplifier to enhance the proportionality between the audio reference and driving force without compromising on loudspeaker damping. The Hybrid amplifier combines a sliding mode controlled amplifier (SMCA) and a linear controller, designed after exhaustive modeling of the input–output behavior of the SMCA and best-fit approximation of the loudspeaker impedance. An 8 W, 500 Hz to 20 kHz prototype of the proposed amplifier is fabricated on the basis of the presented design. Time and frequency-domain results obtained with the experimental hardware are presented to validate the performance improvement. • Enhancing linearity between the audio input and the loudspeaker driving current • Accurate modelling of integrated amplifier-loudspeaker system • Proposing a Hybrid control strategy to improve the audio quality • Development of 8 W laboratory prototype and experimental validation [ABSTRACT FROM AUTHOR]

Due to the rise of distributed energy resources (DERs), virtual power plants (VPPs) have gained intensive academic and industrial attention. While current centralized VPPs benefit from their large aggregated capacity in the wholesale market, they lack effective incentivizing participants for asset investment and market participation. Conversely, the peer-to-peer (P2P) market offers better profits for prosumers through direct trading; however, transactions hinge on approval from associated authorities, such as electricity retailers, who read their power meters. Such an approval procedure becomes complex, even impossible, when more retailers are involved. Hosting the P2P market in a VPP environment can conveniently resolve this issue. This paper proposes a novel holistic P2P (H-P2P) market model hosted in a VPP environment to provide the VPP participants with financial incentives and optimize the network and market operations simultaneously. The proposed new market structure and trade principle allow the proposed H-P2P market to trade active and reactive energies for both financial benefits and network constraints. Using the novel transactive voltage/VAR control (TVVC) method proposed in this paper, the reactive energy trading through the P2P market can support effective voltage regulation and incentivize the VPP participants to provide such voltage control ancillary services actively. Finally, a novel multi-stage P2P negotiation process is introduced to divide the VPP regulatory, active and reactive energy convergence stages, which allows faster P2P decision-making with improved computing efficiency than the conventional multi-period alternating direction method of multipliers (ADMM). The case study validates that the proposed H-P2P market can increase the financial incentives of the prosumers who install PVs and batteries by a large extent and the pure load units by a relatively smaller percentage. [Display omitted] • A novel synergistic model integrating a holistic P2P market in an internal centralized VPP environment. • Simultaneous active and reactive energy trading in the holistic P2P market regulated by the VPP coordinator. • A novel transactive voltage/VAR control concept with P2P reactive energy trading for the internal VPP voltage control. • An innovative multi-stage P2P negotiation mechanism to converge the active and reactive energy transaction decisions. [ABSTRACT FROM AUTHOR]

For an islanded bipolar DC microgrid, a special problem of making the better compromise between a state-of-charge (SOC) balance among multiple battery energy storage units (MBESUs) in positive and negative polar, and bus voltage balance, should be considered. In order to solve this problem, three kinds of the simplified load equivalent circuits on the different operation status of voltage balancer (VB) are established; based on these equivalent circuits, the SOC unbalance mechanism is analyzed and the rules of SOC deviation and voltage unbalance factor are summarized, which are influenced by micro-source and load changing; then a SOC automatic balancing strategy among MBESUs with a voltage balance function is proposed in this paper. The proposed controlling strategy takes into consideration the energy flow relationship under various working conditions; with the aim of controlling the equilibrium time and energy flow direction of SOC, creates a SOC balancing power bridge with the SOC deviation as the main control variable; adopts the adaptive virtual resistance algorithm for both positive and negative BESUs according to the variation rule of the SOC deviation. When the SOC deviation is significant, according to the net power difference of the system, the values of the virtual resistances can be adaptively adjusted to alter the operation mode of BESUs and the VB control strategy is also adjusted so as to ensure the stable running of the system and accelerate the SOC balancing speed via maximizing the balancing power by VB. In order to decrease the voltage unbalance on SOC balancing, apart from adding bus voltage recovery control to the positive and negative batteries, the virtual resistances are related to the SOC deviation when the SOC deviation is slight. The simulation results demonstrate that the control strategy proposed in this paper can quickly realize SOC balancing when the SOC deviation is significant, has superior equilibrium performance as load and micro-source power varying when the SOC deviation is slight, and is also feasible in decreasing the bus voltage unbalance. • A SOC balancing control strategy for energy storage units with a voltage balance function is proposed. • An analysis of SOC trends is carried out in response to the power changing of loads and micro-source. • An adaptive virtual resistances algorithm is coordinated with the control strategy of VB to accelerate the balance process. • Adaptive virtual resistances and a bus voltage recovery control are employed to improve the voltage unbalance factor. [ABSTRACT FROM AUTHOR]

This paper proposes a voltage compensator for converters in multi-converter DC microgrids (MG), which enhances the DC-MG behavior under fault conditions. Among the four existing categories in the classification of the faults, this paper focuses on those faults that affect voltage generation of converter-based distributed generation units (DGUs). Such faults conceptually occur from the terminal voltage reference to actual voltage generated by DGUs. To compensate the adverse effects of the faults, an adaptive scheme is proposed, which considers the most general case of the faults by using the time-varying multiplicative and additive fault models. The proposed scheme benefits from an integrated structure, which does not require separate fault detection, isolation, and identification blocks. As an advantage of the proposed approach, it is designed independent of the primary and secondary controllers of DGUs, and hence its performance is not affected by using different primary and secondary controllers. The effectiveness of the proposed scheme is verified under various fault conditions and uncertainty in the system parameters. Using the proposed scheme, the results show that the performance of system under the fault condition is similar to that of the normal operation. • An adaptive voltage control compensator scheme is proposed for DC microgrid. • The considered faults affect the voltage generation of DGUs. • The faults are modeled by time-varying multiplicative and additive components. • The proposed scheme does not need any separate fault detection and isolation modules. • To validate the conducted analysis, various case studies are provided. [ABSTRACT FROM AUTHOR]

• Propose a SMPC based voltage regulation scheme to coordinate DG, OLTC, SVR and CBs considering uncertainty of DG outputs. • Use the time-correlated scenario generation method in the proposed SMPC framework. • Consider the single-phase regulation effect of OLTC, DGs and CBs. With the increasing penetration of renewable energy resources, the uncertainty of renewable energy resources output introduces challenges to voltage control in distribution networks (DNs). To solve these problems, this paper proposes a double-time-scale voltage control scheme for unbalanced DNs based on stochastic model predictive control (SMPC) to coordinate multiple voltage control devices. In fast-time-scale control, the active and reactive power outputs of distributed generators (DGs) are optimized to minimize voltage deviation, active power curtailment and reactive power fluctuation. In the slow-time-scale control, optimal tap changes of on-load tap changers (OLTC), step voltage regulators (SVR), and switched capacitor banks (CBs) are calculated to reduce voltage deviation and tap operations. Additionally, in the fast-time-scale control, the SMPC-based scheme adopts a scenario generation approach to represent the uncertainty of DG output. Considering the temporal correlation of the DG output, different prediction scenarios and scenario probabilities are obtained by the empirical cumulative distribution function fitted by the historical measurement data. In this paper, the effectiveness of the proposed double-time-scale voltage control scheme is verified by the unbalanced IEEE123 node system. The case study demonstrates that the proposed voltage scheme can effectively keep the three-phase voltages in unbalanced DN within the secure operation range and achieve better voltage profiles. [ABSTRACT FROM AUTHOR]

[Display omitted] • A physics-informed fast voltage control method of distribution network is proposed. • It develops a novel deep reinforcement learning algorithm with graph knowledge. • The proposed algorithm uses multiple agents with continuous action space. With the recent rapid uptake of photovoltaic (PV) resources, the overvoltage condition during low load periods or intermittent renewable generation is one of the most critical challenges for electricity distribution networks. Traditional model-based local or centralized control methods that rely on proper system parameters are difficult to mitigate rapid changes in power systems. Utilizing model-free/data-driven multiagent deep reinforcement learning (MADRL) has been recognized as an effective solution to active voltage control. However, existing MADRL-based control approaches trained solely on data are agnostic to the underlying real-world physics principles. Therefore, this paper aims to incorporate physical knowledge of regional distribution networks into MADRL's decision-making. The main contributions of this paper are summarized as follows. First, a novel physics-informed MADRL -based distributed voltage control method is proposed, which is still under a centralized training and distributed execution framework and only requires local measurements. Second, graph neural networks are employed to help MADRL agents learn graph knowledge (node features and topological information). Further, transformer is introduced to extract discriminative representations and ensure agents' cooperative control. Third, we adopt a physics-guided architecture of neural networks in the actor network to stabilize the training process and improve sample efficiency. Finally, simulation results based upon modified IEEE 33-bus and 141-bus networks validate the proposed method's effectiveness, robustness and computation efficiency. [ABSTRACT FROM AUTHOR]

• The proposed voltage control method provides optimal voltage profiles in various LVDC and MVDC electric railway systems by minimizing inter-area voltage drops. • The proposed voltage control method maximizes the release of the line capacity and minimizes the power losses by minimization of inter-area current. • The proposed voltage control method is a decentralized and distributed voltage control method that employs the DC voltage of DC electric railway networks rather than telecommunication systems. • The proposed voltage control method benefits from simplicity, cheapness, high reliability, expandability and modularity. • Any changes in the power, number and location of trains, traction substations, distributed generators, ESS's and the length of electric lines in LVDC and MVDC electric railway systems cannot perturb the performance of the proposed voltage control method. The medium voltage DC (MVDC) electric railway system is one of the most interesting options for future high-speed rail (HSR) lines. The dc voltage control is one of the most critical challenges of MVDC electric railway systems due to various reasons such as simultaneous, continuous and considerable changes in the power and location of trains, regenerative brake energy of trains, long power lines, the application of ESS's and RES's. In this paper, a voltage control, i.e., the optimal-voltage voltage-power (OVVP) control method, is presented for MVDC electric railway systems. OVVP control method is a practical, reliable, automatic, and modular distributed voltage control method. The proposed voltage control method satisfies the nearest voltage to the nominal value in each node and the smoothest voltage profile in different MVDC electric railway systems. Although the analyses carried out in this paper analytically prove the significant performance of the presented voltage control method, different challenging scenarios are considered to verify OVVP control method more. In addition, the results of the proposed voltage control method are successfully validated by GAMS software. [ABSTRACT FROM AUTHOR]

This paper presents a new Global Fast Non-singular Terminal Sliding Mode Controller (GFNTSMC) that delivers high-precision tracking of high-frequency trajectories when applied to a piezo-driven nanopositioner. The control scheme is realized by combing inverse hysteresis model and global fast non-singular terminal sliding mode compensation. The inverse Bouc–Wen hysteresis model is used to calculate the required hysteresis-compensating feedforward control voltage according to the reference signal. The key uniqueness of the proposed control strategy is it's red global fast convergence, achieved with high accuracy and high bandwidth. The stability of the reported GFNTSMC controller is proved with the Lyapunov theory. Its performance is verified through experimentally recorded tracking results, and its superiority over three benchmark control approaches, namely the Proportional–Integral–Derivative (PID), the Positive Position Feedback with integral action (PPF+I) and the conventional linear high-order sliding mode controller (LHOSMC) is demonstrated through comparative tracking error analysis. Its wide-band stability as well as its significant robustness to parameter uncertainty is also showcased. • A high-order global fast nonsingular terminal sliding mode controller is proposed. • The stability and robustness of the controller are proved with the Lyapunov theory. • The system state can quickly reach the equilibrium point from any initial state. • Experimental results demonstrate significant accuracy improvement and superior robustness. [ABSTRACT FROM AUTHOR]

The unbalanced grid voltage and circuit parameter uncertainty are two main obstacles for three phase voltage source rectifiers (VSRs) to achieve high performance in the practical applications. According to the instantaneous power model of the three-phase VSRs, six power components have to be well-regulated using only four available current manipulated variables, which is a typical underactuated problem. The model predictive control (MPC) provides a unified framework to regulate six power components simultaneously. However, how to balance the six power components control efforts is a challenge task. Meanwhile, the predictive model maybe inaccurate because of circuit parameters uncertainty, which degrades the performance of the MPC as well. In this paper, a robust model predictive power control (RMPPC) method is proposed for the three-phase VSRs to overcome above twice obstacles. The contributions of the work are: (1) The proposed method achieves the balance six power components control of the three-phase VSRs under unbalanced grid by using the off-line optimized weights; (2) a soft robust item with time variant boundary is proposed to achieve robust predictive model to deal with parameter uncertainty. Comparing with the existing voltage oriented control (VOC), direct power control (DPC) and model predictive control (MPC) methods, the proposed method achieves the best power quality in the sense of highest power factor and the lowest power oscillation in experiment, which verify the superiority of the proposed method. • Robust power predictive control is achieved for VSRs under parameters uncertainty. • Optimal balance and simultaneous control for six power components is achieved under the MPC frame. • Satisfactory power quality of three-phase VSR system under unbalanced grid is achieved. [ABSTRACT FROM AUTHOR]

Environmental and sustainability concerns have caused a recent surge in the penetration of distributed energy resources into the power grid. This may lead to voltage violations in the distribution systems making voltage regulation more relevant than ever. Owing to this and rapid advancements in sensing, communication, and computation technologies, the literature on voltage control techniques is growing at a rapid pace in distribution networks. In particular, there is a paradigm shift from traditional offline centralized approaches to distributed ones leveraging increased and varied types of actuators, real-time sensing, fast and efficient computations, and an overall distributed situational awareness. This paper reviews state-of-the-art voltage control algorithms, summarizes the underlying methods, and classifies their coordination mechanisms into local, centralized, distributed, and decentralized. The underlying solution methodologies are further classified into two categories, open-loop and feedback-based. Two specific example workflows are provided to illustrate these solutions for voltage regulation. [ABSTRACT FROM AUTHOR]

This paper proposes a harmony search (HS) based H-infinity (H ∞) control method to promote the conventional droop control method. The proposed method is used to enhance the performance of the voltage/frequency (V/F), controller. It can regulate both voltage and frequency to their rated values while enhancing autonomous microgrid (MG) power quality. The results gained from the proposed controller were compared with the results achieved by using the model predictive control (MPC) technique to show the applicability of the proposed controller. On top of that, a comparison between different controllers presented in this paper is performed. • Controlling the islanded MG voltage and frequency and improving its power quality. • Enhancing the performance of the droop control by applying the H ∞ robust control. • Proposing HS-based H ∞ control method to obtain the controller weighting parameters. • Investigating the system stability and the multiplicative stability margin (MSM). • Performing robustness analysis in the presence of parameters uncertainties. [ABSTRACT FROM AUTHOR]

Static Synchronous Compensation (STATCOM) is considered as one of the famous modules of the Flexible AC Transmission Systems (FACTS) devices. This paper discusses the optimum voltage control technique using the STATCOM module with the transmission system to overcome the drop and the influence factors for the voltage in the power system. In addition, this paper discusses the impact of using the zigzag transformers with the STATCOM control system to prevent the combination between the STATCOM injection voltage and the harmonics to reach pure voltage compensation. The simulation in this paper uses the MATLAB/Simulink software to introduce the STATCOM operation steps, also the proposed analysis of the distribution system network has been validated with IEEE-14 busbar system as a case study to test the increasing loadability by using STATCOM module for enhancing the power system quality. [ABSTRACT FROM AUTHOR]

An Electric Solar Wind Sail is a propellantless propulsion system that gains thrust from the interaction of solar wind particles with a grid of long and charged tethers, which are deployed by spinning the spacecraft about its symmetry axis. In an ideal arrangement, the tethers are all stretched out and the sail takes the shape of a spoked wheel. Actually, the solar wind dynamic pressure warps the tethers and, therefore, the expressions of thrust and torque vectors are difficult to predict in analytical form. Recent works have shown that the bending of the tethers induces a disturbance torque, which can be counterbalanced through a modulation of the tether electrical voltage. Under the assumption that the Electric Solar Wind Sail behaves like an axially-symmetric rigid body, this paper proves that a modulation of the tether electrical voltage is also a feasible option for actively controlling and maintaining the spacecraft attitude. The proposed control law, which is analytically derived as a function of time and spacecraft attitude, is validated through numerical simulations. • This paper discusses a strategy for controlling and maintaining the E-sail attitude. • The attitude is controlled by modulating the voltage of each charged tether. • Numerical simulations show that a small electric voltage modulation is required. • The control law is suitable for a (nearly) axially-symmetric E-sail. [ABSTRACT FROM AUTHOR]

This paper proposes an improved hierarchical control strategy consists of a primary and a secondary layer for a three-phase 4-wire microgrid under unbalanced and nonlinear load conditions. The primary layer is comprised of a multi-loop control strategy to provide balanced output voltages, a harmonic compensator to reduce the total harmonic distortion (THD), and a droop-based scheme to achieve an accurate power sharing. At the secondary control layer, a reactive power compensator and a frequency restoration loop are designed to improve the accuracy of reactive power sharing and to restore the frequency deviation, respectively. Simulation studies and practical performance are carried out using the DIgSILENT Power Factory software and laboratory testing, to verify the effectiveness of the control strategy in both islanded and grid-connected mode. Zero reactive power sharing error and zero frequency steady-state error have given this control strategy an edge over the conventional control scheme. Furthermore, the proposed scheme presented outstanding voltage control performance, such as fast transient response and low voltage THD. The superiority of the proposed control strategy over the conventional filter-based control scheme is confirmed by the 2 line cycles decrease in the transient response. Additionally, the voltage THDs in islanded mode are reduced from above 5.1% to lower than 2.7% with the proposed control strategy under nonlinear load conditions. The current THD is also reduced from above 21% to lower than 2.4% in the connection point of the microgrid with the offered control scheme in the grid-connected mode. • This paper proposes an improved hierarchical control strategy for a three-phase 4-wire islanded microgrid under unbalanced and nonlinear load conditions. • The superiority of the proposed control strategy over the conventional SCC-based control scheme was confirmed by the 2 line cycles decrease in the transient response. • The compensation of both negative and zero sequence harmonics, simple control structure and insensitivity to frequency variations have given this control scheme an edge over the conventional control strategies. The voltage THD of the grid-forming power converters were reduced from above 5.1% to lower than 2.7% with the suggested controller under nonlinear load situations. • Zero reactive power-sharing error has given this control strategy an edge over the conventional droop control scheme in three-phase 4-wire islanded microgrids. [ABSTRACT FROM AUTHOR]

• The design of a voltage stability control strategy for the operation condition of the 300MVA motor generator is described. • The control parameters can be optimized quickly based on the simulation model. • The control method is simple and applicable, and the debugging is convenient. • The simulation results and experimental results of the voltage stability control are shown. In order to meet the power supply requirements of HL-3 tokamak, a 300 megavolt-ampere(MVA) motor generator(MG) is required to provide a stable output voltage during the experiment. The 300MVA MG adopts the working mode of mechanical energy storage and pulse discharge. During the discharge, the rotational speed of the MG decreases rapidly. When the MG feeding the high power load, the voltage fluctuation is large, which has an adverse effect on the control of the DC power supply system between the MG and the load. In this DC power supply system, the input voltage fluctuation should be less than 10 %. When the voltage fluctuation is maintained at 5 % or less, better control effect can be achieved. In this paper, through using the methods of mathematical modeling, simulation analysis and experimental verification, the control strategy of 300MVA MG output voltage based on excitation voltage control is designed. According to the power supply condition, a simulation model of a 300MVA six-phase MG feeding the central solenoid(CS) coil through high-power phase-controlled power supply is established. Based on this, the steady-state and dynamic operation performance of the MG model is simulated. The simulation and experimental results show that the output voltage static error and fluctuation of the MG are small. And the system response speed is fast, which can realize the stable voltage control of the MG. [ABSTRACT FROM AUTHOR]

Due to the increasing high penetration of Photovoltaic (PV), it brings great challenge for voltage control issue of distribution network. To address this problem, this paper presents an improved collaborative Multi-Agent Reinforcement Learning (MARL) approach for proactive voltage control, aimed at mitigating voltage violations and minimizing power losses. The self-attention mechanism is embedded into the multi-agent soft actor-critic (MASAC) algorithm to enhance the collaboration of multi-agent system, which can well improve the learning efficiency to ensure the voltage safety of Distribution Network. In addition, the proposed learning approach is implemented on IEEE 33-bus, 141-bus and 322-bus systems, and the simulation results reveal that the proposed approach can control the voltage into safety domain as well as reduce power losses. [ABSTRACT FROM AUTHOR]

• The core of the novelty of NV-MAIS approach relies on the fact that we are using shunt reactors for both voltage regulation and frequency oscillation damping. To the best knowledge of the authors, there has not been reported the use of the shunt reactors in frequency oscillation damping and the NV-MAIS strategy is the first of a kind of such an approach with grid commissioning and installation in high voltage 735-kV transmission level. The Hydro-Québec transmission system is among the most extensive and complex power grid in North America due to its very long lines (over 1000 km) joining the generation facilities in the north of the Québec province to the main centers of consumption in the south. Since the 1990s, Hydro-Québec has adopted a defense plan, consisting of various types of protection solutions including different remedial action schemes (RAS) and automatic action strategies, to increase the stability and reliability of its transmission system against extreme contingencies. One of these protection strategies is the automatic switching of shunt reactors (MAIS) 1 MAIS is the acronym of the French name of the project as M anoeuvre A utomatique d' I nductance S hunt (MAIS). which has been in operation since 1997. The goal of the MAIS system is to keep the voltage profile of the whole 735-kV grid in an acceptable range to increase the transmission capacity. The MAIS system at each substation is entirely independent from neighbour substations and will close or trip shunt reactors just based on local measurements. As a periodical upgrade in all existing protection solutions in the Hydro-Québec power system, new functionalities have been added into the existing MAIS system to develop its new version to improve both the voltage profile and the frequency response. This paper presents this new version including the algorithm and the concept behind the new additional functionalities. The simulation results show the efficiency and performance of the proposed method. On that basis, a deployment on Hydro-Québec's grid to replace almost all the existing MAIS system with this new version will be realized by 2030. [ABSTRACT FROM AUTHOR]

This paper deals with a novel hybrid transformer configuration for MV/LV three-phase distribution systems. The configuration involves a standard distribution transformer with an open-end secondary winding, which is connected to the LV grid and a four-legged inverter with a floating DC bus. Unlike previous hybrid transformers, the proposed configuration eliminates the need for a bidirectional converter and auxiliary transformer windings as well. The fourth leg of the inverter is exploited to manage the neutral line current. The main advantage of the proposed configuration is its ability to provide phase voltage control at the distribution grid edge. This enables the compensation of various grid voltage anomalies such as sags, swells and some kinds of interruptions. The effectiveness of the proposed configuration is demonstrated through simulation and experimental results, highlighting its promising performance in real-world scenarios. [ABSTRACT FROM AUTHOR]

• An unprecedented very large-scale T&D dataset covering Texas is made publicly available. • The sheer size of this dataset is intended to provide a challenge for the scientific community. • This lays the foundation for demonstrating the coordination of T&D. • It can help foster the improvement of algorithms and tools for years to come. Distributed energy resources, such as rooftop solar, have rapidly expanded in recent years, given declining costs and the desire to reduce carbon emissions. With more energy resources located in the lower-voltage distribution system, it is increasingly helpful to utilize combined transmission and distribution (T&D) system models to analyze interactions between these normally-distinct subsystems. This paper proposes a methodology for creating very large-scale, highly detailed, combined T&D systems that are synthetic—that is, free from non-public data—yet still realistic. The methodology creates very large-scale combined T&D systems by merging the most up-to-date techniques for creating synthetic distribution feeder networks with the latest methods for building synthetic, meshed bulk-power transmission networks. This methodology is demonstrated on a T&D system geolocated in Texas, and benchmarked with co-simulation results. Validation demonstrates that the resulting syn -texas-TDgrid synthetic test system realistically represents characteristics found in actual networks, addressing the lack of available T&D test systems. With over 15,000 feeders and 46 million electrical nodes, this T&D dataset has applications for research in optimal power flow algorithms, voltage control, reconfiguration, and T&D coordination schemes under high adoption of distributed energy resources. [ABSTRACT FROM AUTHOR]

• Propose a new real-time distributed voltage control scheme for MV&LV DNs based on ATC method. • Coordinate multiple DGs at different voltage levels to guarantee secure operation of the entire DN. • Design a dynamic allocation approach to determine the weighting factors for the optimization problem of MV&LV DNs. This paper proposes a new real-time distributed voltage control (RTDVC) scheme for medium and low voltage (MV&LV) distribution networks (DNs) based on the analytical target cascading (ATC) method. In this scheme, photovoltaic (PV) units at the LV level, on-load tap changer (OLTC) and distributed generation (DG) clusters at the MV level are optimally coordinated to regulate the bus voltages in MV&LV DNs to be close to the nominal value while minimizing the number of operations of OLTC and smoothing the reactive power outputs of DGs. Based on the ATC method, the large-scale strongly coupled voltage control problem of MV&LV DNs is decomposed into several subproblems while guaranteeing the optimality of the primal voltage optimization problem. The decomposed subproblems are iteratively solved in parallel in the MV and LV controllers, which achieves optimal voltage control in a distributed manner and effectively reduces the computation burden. An MV&LV test system with two 20 kV feeders and 39 0.4 kV LV grids was simulated to demonstrate the control performance of the proposed distributed voltage control scheme. [ABSTRACT FROM AUTHOR]

Previous research indicates that post-fault grid-forming (GFM) converters only work in current limiting control (CLC) mode. However, converters integrating the current saturation algorithm (CSA) can operate in both constant voltage control (CVC) and CLC modes. This paper firstly derives the angle-switched model of the grid-connected system governed by CSA and virtual synchronous generator (VSG). Then, combining the fault and three types of post-fault trajectories, critical clearing angle is analytically formulated through the Segmental Equal Area Criterion (SEAC). Finally, a range of values for the saturated current angle is proposed to ensure that the system is stabilized in CVC mode. Notably, the optimal saturated current angle, which is the minimum value within the range, provides the maximum critical clearing angle. • An angle-switched model for a virtual synchronous generator equipped with the current limit is established. • Segmental equal area criterion is proposed and analytical formulations are derived for the critical clearing angle under three post-fault operational states. • Optimal saturated current angle control is proposed to enhance transient stability by configuring the saturation current angle. [ABSTRACT FROM AUTHOR]

• A novel active control method is proposed to suppress the milling chatter of thin-walled workpieces. • The non-smooth properties, time delays, multi-modal participation, and varying dynamic characteristics are synthesized together in controller design for the first time. • The combination of robust control and time delay controller enhances the control effect and reduces the control voltage to the single robust control. Chatter phenomena commonly plague the milling process of flexible workpieces, leading to undesirable fluctuations in accuracy and diminished machine efficiency. Limited by complex dynamics of this process, the non-smooth properties, time delays, multi-mode participation, and varying dynamic characteristics have never been considered together in active control. This paper proposes a novel active control method to suppress milling chatter of flexible workpieces by synthesizing these factors together in controller design for the first time. The dynamic model for milling processes of a cantilevered plate, which is regarded as an examined example of flexible structure, is transformed from a time delay differential equation with varying coefficients to a real-time differential equation with constant coefficients by uncertainty transformation. A robust combined time delay control method is tailored for the uncertainty system via combining a robust controller with synthesis method and an active time delay controller. Both simulations and experiments validate the effectiveness and performance advantages. Following the implementation of experiments, the maximum stable milling depth experiences a notable improvement from 0.1 mm to 0.8 mm after control, and is larger than that of 0.6 mm under single robust control. Additionally, under the given milling conditions, the control voltages of robust combined time delay control exhibit a 25 % and 11 % reduction compared to those of the robust control method. The novel combination of a robust controller and time delay controller enhances the control effect and reduces the control voltage. [Display omitted] [ABSTRACT FROM AUTHOR]

Distributed control has been employed in autonomous microgrids (MGs) to attain secondary control goals. However, the reliance of MG's distributed secondary control on communication makes it vulnerable to degraded performance and the risk of instability due to communication delays. This paper enhances the flexibility of the MG control framework, with each distributed generator incorporating supplementary local feedback signals. This added flexibility strengthens the MG's ability to counteract disturbances caused by delays and enhances its dynamic performance. The introduction of extra feedback signals has a direct impact on the dynamic response of the MG, leaving its steady-state condition unaffected. In comparison to the methods found in existing literature, the increased flexibility relaxes the inherent trade-off between the objectives of improved transient response and the system's ability to mitigate disturbances caused by delays. To model the MG, a set of delay differential–algebraic equations (DDAEs) is used. The small-signal linearized model is derived and employed to evaluate the stability of the MG as well as fine-tune the control parameters. The effectiveness of this proposed control structure is demonstrated using the MATLAB/Simulink environment and a controller in the loop (CIL) setup, tested against both fixed universal and asynchronous delays, as well as time-varying delays. • A novel hierarchical distributed control to mitigate communication delays impact. • Enhancing the tolerance for a wide delay range without degrading convergence speed. • Additional feedback terms to the frequency control to enhance disturbance rejection. • Additional feedback terms to the voltage control to enhance disturbance rejection. • Verification via small-signal analysis and simulations in Simulink and CIL setup. [ABSTRACT FROM AUTHOR]

In this paper, a novel distributed data-driven voltage control approach is proposed to handle unexpected voltage violations in active distribution networks (ADNs) with changing system topologies. In the proposed control scheme, once a voltage violation occurs, the PV inverters and battery energy storage systems will be coordinated to provide voltage corrective control. The whole control scheme is designed in a distributed and model-free manner to improve the scalability, reliability, and adaptability in regulating ADNs. In this study, the ADN is firstly divided into several local control regions (LCRs), whose models are identified online with local real-time measurements via a modified multi-layered recursive least squares (m-RLS) method. Then, based on the estimated system model, the whole control approach is realized in a distributed manner by employing a consensus version of the fast alternating direction method of the multiplier algorithm (FADMM). Simulation involving the IEEE 34-bus distribution test system verifies the effectiveness of the proposed control framework and illustrates key advantages of the proposed method, including (i) adapting to online network topology and operating-point changes without an accurate offline system model, and (ii) reaching a comparable control performance with a well-designed centralized controller. • A novel data-driven distributed control approach is proposed to regulate voltages for distribution networks with changing system topologies. • A modified multi-layered recursive least squares method is developed to achieve fast and accurate estimation of the sensitivity model for an active distribution network with topological changes. • To be consistent with the fast time-varying operation conditions in active distribution networks, the fast alternating direction method of the multiplier algorithm method is employed to coordinate the distributed energy resources. • Various case studies are conducted to demonstrate the effectiveness and advantages of the proposed control method, including identification test, control effectiveness test, and comparison with a centralized controller. [ABSTRACT FROM AUTHOR]

• An accurate admittance model for the grid-connected converter with droop control is proposed. • The frequency coupling phenomenon is induced by the asymmetry of the droop controller for the grid-connected converter. • The outer control loop will impact the frequency-coupled phenomenon, but has slight effects on positive and negative sequence admittance of VSCs. • The proportional gain of the current control loop impacts obviously the frequency coupling phenomenon. The droop control scheme is widely applied for the paralleled operation of the grid-connected converter. Yet, the frequency-domain admittance model for the grid-connected converter with droop control is still inaccurate due to the complex coupling relation of the droop control loop, the voltage control loop, and the current control loop. To address this problem, the coupling relationship of these control loops is analyzed in this paper, and then an accurate admittance model for the grid-connected converter with droop control is proposed based on the complex vector modeling method in both dq -frame and αβ -frame. The influence of different control parameters on the admittance model is analyzed further. The proposed model accurately describes the admittance characteristics of the grid-connected converter with droop control, and reveals the frequency coupling phenomenon caused by the droop control loop. The frequency response measured by frequency scan and simulation results verify the effectiveness of the established model. Finally, the impedance interactive stability analysis results show that the grid-connected converter with droop control is prone to instability in stiff grid conditions. © 2017 Elsevier Inc. All rights reserved. [ABSTRACT FROM AUTHOR]

For islanded microgrids with inverter-based distributed generators (DGs), this article focuses on the fast finite-time secondary voltage and frequency control problem considering system uncertainties. The distributed controller is designed based on the command filtered backstepping procedure, and a disturbance observer is constructed to estimate the lumped system uncertainties (including parameter perturbations, unmeasurable variables, etc.). In addition, the singularity issue derived from differentiating the virtual control law is avoided by using a smooth switch function. The proposed controller guarantees that the tracking errors of voltage and frequency converge to a small region around the origin in a finite time, while achieving desired active power sharing ratio. Case studies are conducted on a microgrid system to demonstrate the effectiveness of the proposed strategy in the presence of load changes and parameter perturbations. • This paper aims at achieving fast finite-time secondary control of islanded microgrids. • The proposed method is free of chattering and singularity issues. • The disturbance observer is constructed to enhance the robustness of voltage control. • Case studies are conducted to verify the effectiveness of the proposed strategy. [ABSTRACT FROM AUTHOR]

This paper suggests a methodology for the identification, classification, and evaluation of various types of interactions that may occur in an HVDC link based on modular multi-level converters (MMC). The methodology incorporates the most suitable analytic tools for the frequency-domain study of each interaction category. To do so, a detailed nonlinear model of an MMC-based HVDC link that consists of master and slave MMCs, AC grids, and the DC transmission system is derived. Then, it is linearized to obtain a multi-input multi-output (MIMO) linear model that represents the dynamics of the complete MMC-based HVDC link. Based on the control loops of interest, interactions are classified as (1) state variable interactions, (2) disturbance interactions, (3) control loop interactions, and (4) overall system interactions. Then, through the application examples, the mentioned four categories of interactions are studied in frequency domain via the relevant analytic tools. The results obtained from the frequency-domain analysis are validated by time-domain simulation. • A methodology for evaluation of interactions in HVDC systems is suggested • Interactions caused by the cable parameters can destabilize the system • DC voltage control loop and total energy control loops are highly coupled • Active power loop is decoupled from DC voltage and total energy control loops [ABSTRACT FROM AUTHOR]

Highlights • Jacobi-proximal ADMM is applied to design peer-to-peer grid voltage support function. • Push-sum gossip protocol is proposed as the underlying communication protocol. • Linear voltage model is used to predict the voltage. • The proposed algorithm is much faster than the Jacobi ADMM and the Dual Decomposition. • The proposed algorithm succeeds in regulating the voltages within a reasonable time. Abstract The increasing penetration of renewable energy sources is impacting the operation of the distribution grid. Whilst they are currently placing a burden on the distribution grid, it is generally agreed that these sources could also be used for active grid control, thereby contributing to a stable and secure grid. Smart photovoltaic inverters can contribute to active grid control, by expanding their features with added functions. In this paper, we develop a novel grid voltage support algorithm for smart photovoltaic inverters, based on distributed optimization and peer-to-peer communication. The Jacobi-Proximal Alternating Direction Method of Multipliers is applied in this paper to locally optimize reactive power compensation and active power curtailment of each inverter participating in the voltage control. We propose the use of a push-sum gossip protocol to enable peer-to-peer data interchange between inverters. We also use strategies to improve the robustness of the proposed algorithm: an acceleration strategy, a feedback strategy and an anti-windup strategy. A case study is presented, demonstrating the fast convergence of the algorithm and its ability to solve the voltage problems. [ABSTRACT FROM AUTHOR]

Abstract The significant increase of high-power renewable energy sources (e.g., off-shore wind energy systems) in the power networks, has introduced Multi-Terminal High-Voltage DC (MTDC) grids as a prominent approach for transmitting power with high reliability, security, and efficiency. Nonetheless, MTDC systems introduce several challenges pertinent to operation. This paper investigates optimal power flow in MTDC networks to minimize the transmission power loss via DC voltage control, which is an essential approach for the MTDC network operation to maintain the transmission balance and grid stability. In this paper, a generalized approach for minimum transmission power loss in radial and mesh MTDC networks is presented. Voltage droop control is employed in the radial network, with droop characteristics tuned for optimal power flow, which is supported by an optimization approach. Radial MTDC networks with either a common interconnection node or a common interconnection line are considered. While for the mesh network and due to the difficulty of adjusting the droop gains, an optimization algorithm is merely devised for optimal power flow. A modified CIGRE B4 network is employed in this paper to investigate the presented concept considering several scenarios. Simulation results using the Matlab platform are shown to validate the paper's contribution. [ABSTRACT FROM AUTHOR]

The goal of this paper is to design an adaptive optimal controller for voltage control of DC–DC Z-Source (ZS) converters under a challenging load situation called Constant Power Load (CPL) without a need for any knowledge about their dynamics. These converters have been developed to remedy the drawbacks of the conventional converters and several works have been recently carried out to increase the voltage gain and decrease the voltage stress in these converters. Meanwhile, from a control point of view, voltage control of a very high voltage gain ZS DC–DC converter is unquestionably more sophisticated than the traditional converters (like Boost). Firstly, due to the non-minimum phase functionality, ZS converters present an additional challenge to controller design processes compared with traditional converters. Secondly, their output voltage sensitivity is high, and small oscillations in the control signals can lead to large oscillations in the output voltage. On the other hand, CPLs can further threaten the performance of the converter's voltage controller due to incremental negative resistance. To alleviate these problems Reinforcement Learning (RL), one of the promising optimal and adaptive model-free control algorithms, can be used. Contrary to traditional controllers which manipulate PWM's duty cycle, here the proposed controller directly controls the power switches inside the converter. Due to the fact that the action space is discrete and finite, this gives rise to significant simplifications in the architecture of the RL-based controller and better convergence in the training phase. Voltage control of various ZS converter topologies can be carried out by the proposed algorithm. In this paper, for instance, it is experimentally applied to a quasi ZS converter under CPL condition, and its performance compared to other classical controllers such as single-loop PI controller, dual-loop PI controller, and finite state model predictive controller is reported which confirms the better performance of the proposed algorithm in terms of voltage stability and transient tracking error. [ABSTRACT FROM AUTHOR]

This paper presents a voltage control mode (VCM)-based super-twisting algorithm-sliding mode controller (STA-SMC) and current control mode (CCM)-based STA-SMC for islanded and grid-connected operations of single-phase inverters interfaced with distributed energy resources (DERs), respectively. The external disturbances are modeled by considering the effects of load currents or load voltages depending on operational modes whiles parametric uncertainties are modeled based on their variations from nominal values. Therefore, the proposed controllers are robust against external disturbances, parametric uncertainties, and variations in loading conditions. Simulation studies are conducted in the MATLAB/Simulink platform for both single and multiple DERs which are interfaced through single-phase inverters to the main grid or loads. The results are also analyzed through comparative studies with different controllers and it is found that the proposed controllers perform better than existing controllers. • A VCM-based STA-SMC is designed for islanded operations of DERs. • A CCM- STA-SMC is designed for grid-connected operations of DERs. • The robustness is analyzed against external disturbances and parametric uncertainties. • Performances are evaluated under different loading conditions. [ABSTRACT FROM AUTHOR]

This paper proposes a low-complexity online state of charge estimation method for LiFePO 4 battery in electrical vehicles. The proposed method is able to achieve accurate state of charge with less computational efforts in comparison with the nonlinear Kalman filters, and also can provide state of health information for battery management system. According to the error analysis of equivalent circuit model with two resistance and capacitance, two proportional-integral filters are designed to compensate the errors from inaccurate state of charge and current measurements, respectively. An error dividing process is proposed to tune the contribution of each filter to the finial estimation results, which enhances the validation and accuracy of the proposed method. Recursive least squares filter can provide the state of health information and updates the parameters of battery model online to eliminate the errors caused by parameters uncertainty. The proposed method is compared with extend Kalman filter in regards to accuracy and execution time. The execution time of the proposed method is measured on Zynq board platform to validate its suitability for online implementation. In this paper, the proposed method is able to obtain less than 1% error for state of charge estimation. [ABSTRACT FROM AUTHOR]

A substantial part of electricity bills in commercial buildings can consist of demand charges. Lowering the peak power and/or reducing the hours that a power threshold is exceeded can drastically reduce demand charges. The ability to do so by dynamic, operational adjustments reflects the “energy flexibility” of the building. This paper targets the optimal combination of design and operational measures in a retrofit or new design project that delivers the most effective way of reducing demand charges by increasing energy flexibility and efficiency of commercial buildings. This goal is achieved through an analysis of all feasible energy consumption and peak reduction measures in different building types and in different use contexts. A search algorithm that compares all possible interventions will deliver the optimum. This leads to a stochastic optimization approach with recognition of the effects of all possible sources of uncertainty. This paper evaluates the measures that are commonly adopted to decrease energy consumption and increase energy flexibility, including (1) upgrading building components and installing energy efficient equipment; (2) applying dynamic building load control strategies; (3) installing a rooftop photovoltaic panel array. Operational interventions include the manipulation of thermostat settings and the voltage reduction of lighting and appliances (in some cases including HVAC components) in the building, which may cause some level of thermal and visual discomfort during certain periods. In order to support retrofit and design improvement decisions, an approach is developed to find the optimal mix of measures that maximize the net present value of the investment in all measures over twenty years for the owner. This paper analyzes the optimal solutions for three commercial building types, office, hospital, and retail. The paper suggests a modeling and optimization framework that can be used by building designers and operators to make optimal investment decisions to reduce demand charges. The paper shows a novel support of the decision making by building operators when faced with the opportunity to reduce demand charges. [ABSTRACT FROM AUTHOR]

This paper describes the designing and analysis of a class – A Chopper in open loop as well as closed loop control. This paper aims to put up the results based on software as well as hardware simulation. DC chopper is realized by using dSPACE DS1104 for open loop operation of class – A chopper with resistive load. In this paper, computed values are compared with measured values and accordingly error is calculated. In closed loop control of chopper, voltage control strategy is implemented using MATLAB 2016a. Improved results illustrate the effectiveness of closed loop control strategy. [ABSTRACT FROM AUTHOR]

This paper studies the power electronic converters for grid connection of axial flux permanent magnetic synchronous generators (AFPMSG) based variable speed wind turbine. In this paper, a new variable speed wind turbine with AFPMSG and Z-source inverter is proposed to improve number of switches and topology reliability. Besides, dynamic modeling of AFPMSG is presented to analyze grid connection of the proposed topology. The Z-source inverter controls maximum power point tracking (MPPT) and delivering power to the grid. Therefore other DC–DC chopper is not required to control the rectified output voltage of generator in view of MPPT. As a result, the proposed topology requires less power electronic switches and the suggested system is more reliable against short circuit. The ability of proposed energy conversion system with AFPMSG is validated with simulation results and experimental results using PCI-1716 data acquisition system. [ABSTRACT FROM AUTHOR]

With the increasing penetration of renewables, microgrid integration has been considered as one of the most promising approaches to enhance the utilizations of various types of energy resources in smart distribution systems. In the near future, with the higher levels of intermittent renewables are envisaged, the distribution network operators will face significant challenges to the control and operation of distribution networks dispersedly. Consequently, the development of effective and motivating ancillary service schemes in a decentralized way for executing real-time control and reducing calculation and communication burden is still in its infancy and needs to be researched. To address this issue, this paper explores an optimal voltage regulation method with the participants of multi-microgrids based on multiple agent systems. Without an arbitration agent, peer agents in the multiple agent system calculate voltage sensitivities by local and neighbourhood measurements only. In this paper, a bi-level game model is proposed for voltage control process. In the upper-level, the distribution network operator searches the reasonable incentive mechanism based on the Stackelberg game. In the lower-level, microgrids make voltage control strategies autonomously based on a static game among microgrids. In the proposed method, microgrids participate in voltage control in distribution networks as ancillary service providers while maximizing their own profits. Meanwhile, the distribution network operator reduces the infrastructure reinforcement and avoids unnecessary renewable energy curtailment. Finally, the feasibility and effectiveness of the proposed method has been demonstrated on a modified IEEE 33-bus system. [ABSTRACT FROM AUTHOR]

When DC-side energy storage batteries participate in frequency regulation, inconsistent inertia requirements exist for frequency deterioration and recovery stages. In addition, the frequency regulation power can lead to the DC overvoltage of the DFIG. To address these issues, this paper proposes a voltage suppression strategy (VSS) during multi-stage frequency regulation with the DC-side energy storage batteries. In the frequency deterioration stage, a SOC segmented feedback inertia control (SSFIC) is developed to reduce the frequency change rate. In the frequency recovery stage, to mitigate transient maximum frequency deviation, a maximum frequency differential inertia control (MFDIC) is constructed by incorporating the transient maximum frequency deviation into inertia control coefficient. In the frequency regulation stage, to decrease the steady state frequency deviation and avoid the secondary frequency drop, an exponential inertia droop control (EIDC) is created by considering the droop coefficient as an exponential function of the frequency change rate. To suppress the DC voltage fluctuation, a DC voltage compensation control (DVCC) is presented to transform the active power of SSFIC, MFDIC and EIDC to the d-axis current compensation increment of GSC. Extensive simulation results have proved that the proposed strategy can successfully enhance the frequency regulation and voltage suppression ability. [ABSTRACT FROM AUTHOR]

The increasing integration of renewable energy resources in active distribution networks (ADNs) aggravates voltage deviations. Fluctuations among distributed generators (DGs) and the absence of accurate network parameters hinder the performance of model-based voltage control method. How to utilize the advantages of measurement-based data-driven method combined with model-based method has become the key to effectively addressing voltage issues. This paper proposes a data-model hybrid-driven adaptive voltage control method for ADNs. A data-model hybrid-driven adaptive voltage control framework containing two hybrid modes is established with the consideration of measurement configuration. In the data-model correction mode, the performance of data-driven control is improved by prior physical knowledge in adequate measurement area. In the data-model coordination mode, the inter-area coordination realizes the complementarity of the regulating ability between the areas with adequate measurement and those without. Finally, analysis and verification are performed based on the modified IEEE 33-node distribution network. The results demonstrate that the proposed hybrid-driven voltage control method has superiority in adaptability to DG fluctuations and strategy interpretability, which obtains satisfied voltage control performance. • Data-model hybrid-driven adaptive control framework for ADNs was established. • Data-model correction mode was proposed to improve data-driven performance. • Data-model coordination mode was proposed to cope with uneven measurements. [ABSTRACT FROM AUTHOR]

The accurate and comprehensive equivalent circuit model (ECM) of Proton Exchange Membrane electrolyzer (PEME) is needed urgently in the design process of power supply for electrolytic hydrogen production such as rectifier or dc/dc converter. However, the existing ECM can only simulate the steady-state and dynamic electrical characteristics of electrolyzer in the electrolysis process under current controlled mode. In this paper, in-situ electrochemical impedance spectroscopy (EIS) is employed to measure the electrode impedance (R) and double-layer capacitance (C) of PEME. It's worth noting that for gaining the value of R and C, only the electrochemical circle fit method is used without further proceeding. Based on this method to identify parameters, a novel and generic ECM of PEME is proposed to simulate stable electrical characteristics of three different PEMEs under current controlled mode and voltage controlled mode, respectively, in the start-up, electrolysis, and turn-off stages. Specially in this model, diodes' switching characteristics are innovatively employed to simulate the start-up stage; on the other hand, an RC circuit connects with the diode parallelly to model the turn-off stage. Moreover, it can precisely characterize the dynamic and transient electrical behaviors of PEME. Finally, the validity of proposed ECM of PEME is verified based on small scale experiments. • The model simulates PEM electrolyzer's electrical characteristics under voltage control. • The model applies to simulating PEM electrolyzer' electrical feature at various power levels and aging stages. • The model can simulate the multi-time scale electrical characteristics of PEM electrolyzers. • The model is based on circuit principles for its modeling approach and no longer employs empirical formulas. [ABSTRACT FROM AUTHOR]

This paper presents a programmable constant temperature anemometer (CTA) with a voltage control of the negative temperature coefficient (NTC) thermistor's working temperature. The CTA uses a non-bridge regulating circuit, outputting voltage, current and power dissipation signals. Its operation and sensitivity control are tested for NTC temperatures in a 45 to 85 °C range, at wind speeds up to 14 m / s. The power sensitivity at 25 m / s is improved by NTC temperature increase, estimated to be 6.74 mW / (m ∙ s − 1) at 85 °C. A qualitative analysis of circuit's stability is derived, providing the guidelines for bandwidth optimization. The NTC's resistance is regulated with error of 0.9 % for working temperatures over 60 °C. The demonstrated programmability of NTC temperature allows for implementation of known temperature compensation and measurement techniques utilizing a single sensor, while permitting continuous sensitivity control. This makes it suitable for measurements with varying ambient conditions. [Display omitted] • A stable non-bridge circuit, with voltage, current and power outputs is realized. • Programmable voltage control of NTC's temperature is demonstrated. • NTC resistance set error of 0.9 % is achieved. [ABSTRACT FROM AUTHOR]

The line shunts are usually ignored by various linear power flow (PF) models in power distribution system analysis, planning and optimization. However, "charging effects" from line shunts of underground/submarine power cables would cause non-negligible model errors for these commonly used PF models. In this paper, we propose a modified Linear Distflow model (LinDist) with line shunts, i.e., LinDistS. We also further propose its extensions considering the ZIP load, weakly-meshed topology and unbalanced three-phase systems. Moreover, the linearization error of voltage component is theoretically analyzed. Case studies show that compared with other models, the proposed LinDistS achieves the descent calculation accuracy and efficiency. We also show the application scope of LinDistS by a Volt/VAr control (VVC) framework with distributed generators, mainly photovoltaic (PV), and the non-negligible "charging effect". Simulation exhibits that with LinDistS, the VVC can optimally dispatch the shunt capacitors and also optimize the real-time reactive power output of PV. Moreover, with LinDistS, the VVC shows better solutions' consistency and higher computing efficiency compared to traditional VVC methods. • A linear distflow model with non-zero line shunts (LinDistS) for distribution systems. • LinDistS further considers ZIP load model, weakly-meshed topology and three-phase unbalanced systems. • Simulation with different comparisons shows LinDistS's high accuracy and efficiency. • A mix-integer linear Volt/VAr control model based on LinDistS is also proposed. [ABSTRACT FROM AUTHOR]

The output voltage tracking problem of a disturbed buck converter is investigated in this paper via a GPI observer-based approach. Control performances of the converters are always influenced by undesirable effects of disturbances. These disturbances usually are of time-varying forms. Conventional backstepping schemes cannot achieve satisfactory performances in handling time-varying disturbances. By adding integral actions into the controller, only the slow-varying disturbances are asymptotically compensated in this way. In this paper, two GPI observers are constructed to estimate the lumped time-varying disturbances. By introducing the disturbance estimations into the design process, a composite GPI observer-based robust control scheme is developed. The proposed algorithm performs a promising disturbance rejection ability. Rigorous stability is guaranteed. Experimental results in the presence of time-varying disturbances are illustrated to show the feasibility of the proposed composite method. [ABSTRACT FROM AUTHOR]

• Measured the electrochemical impedance spectra of three-electrode model cell at different temperatures and state-of-charge. • Obtained the limiting current amplitude of different lithium-deposition-free control strategies. • Analyzed the limitations of different control strategies. • Proposed a lithium-deposition-free control strategy that prevents terminal voltage from exceeding cut-off voltage. Among various methods of preheating lithium-ion cells at low temperatures, alternating current preheating (ACP) has the advantage of high efficiency. However, the risk of lithium deposition exists when using the ACP method. To prevent lithium deposition, terminal voltage control strategy (TVCS), negative electrode potential control strategy (NEPCS) and full cell impedance control strategy (FCICS) are proposed. However, each of the three control strategies has limitations. In this paper, the applicability boundaries of the three control strategies（TVCS, NEPCS, FCICS） are analyzed by measuring the electrochemical impedance spectrum (EIS) of a three-electrode model cell at different temperatures and state-of-charge (SOC). The results show that TVCS leads to lithium deposition when the frequency is lower than boundary frequency, while NEPCS leads to the terminal voltage exceeding the cut-off voltage when the frequency is higher than boundary frequency. As for FCICS, when the SOC is 100 %, 75 %, 50 % and 25 %, the heat generation is decreased by 8.61 % ∼ 34.5 %, 9.18 ∼ 51.7 %, 6.49 ∼ 40.7 % and 8.61 ∼ 61.4 %, respectively, compared with NEPCS. Moreover, the applicability boundary obtained by FCICS also leads to the terminal voltage exceeding the cut-off voltage. Based on the above analysis, this paper proposes a strategy to control the terminal voltage without lithium deposition. When the frequency is lower than the boundary frequency, NEPCS is employed, and when the frequency is higher than the boundary frequency, TVCS is employed. [ABSTRACT FROM AUTHOR]

A large-scale diffusion of photovoltaics (PVs) is expected to disturb the voltage control in an electric distribution network. When PVs generate more electricity than demand requires, the electric voltage may exceed its legal limit, and the PV generation is suppressed by the power conditioner. This paper evaluates the extent to which residential energy management resources (EMR) can contribute to controlling the distribution line voltage and reduce the amount of PV generation suppression while considering the variety among households due to family composition and appliance ownership and the operation constraints due to operation time restrictions, occupants’ comfort and control method (manual control or automatic control). This paper estimates EMR that can be provided by a washing machine, clothes dryer, dishwasher, rice cooker, electric pot, air conditioner and heat pump water heater. EMR varies among households and accounts for 3%–63% of annual household electricity demand. Although 9.9% of PV generation is suppressed when all detached houses have installed PVs in the assumed residential community, the EMR is able to decrease to no more than 3.0%; this reduction potential decreases by 23% owing to the above-mentioned operation constraints. [ABSTRACT FROM AUTHOR]