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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]

With the large-scale integration of renewable energy systems, the power inertia and voltage support of the grid are low. Using the inverter with temporary storage capabilities cope with shortages and power fluctuations. This paper presents a new sensorless control of a single-phase grid-connected PV system based on a multilevel flying capacitor inverter MFCI) able to smooth out the power produced. The designed controller involves two cascade loops, an outer loop control extracts the maximum power despite climate change, and an inner loop consists of a model predictive control based on the Lyapunov theory for power factor correction and flying capacitor voltage balancing. Furthermore, an interconnected Kalman-like high-gain observer is combined with the predictive control algorithm to estimate the flying capacitor voltages accurately based on the actual grid current. The stability study of the suggested observer in the closed loop has been described. An algorithm that generates reference signals to manage power flows is also developed. The performance of the proposed controller has been verified on the MATLAB/Simulink platform, and the simulation results confirm the effectiveness of the proposed controller over different grid operating modes. • the proposed PV system is based on MFC inverter able to smooth out the grid-injected power. • The designed controller combines a Lyapunov-based model predictive control with a Kalman-like high-gain observer. • The PV conversion system optimizes energy extraction, injecting it smoothly into the grid. • The inverter, with temporary storage, copes with power fluctuations without external energy storage during grid faults. • The closed-loop stability of the controller is rigorously proved during the normal mode and grid fault conditions. [ABSTRACT FROM AUTHOR]

Model predictive control (MPC) is an outstanding control method which can achieve superior dynamic response, nonlinear control and multi-objective collaborative control. However, because of unfixed switching frequency, the harmonic spectrum of the output current is dispersed, which would make it difficult to design the output filter. In this work, a double voltage vector model predictive control (DVV-MPC) algorithm for grid-connected cascade H-bridge (CHB) multilevel inverter is presented. The algorithm not only has the advantages of MPC but also produces fixed the switching frequency of the inverter. It is realized by a modulation stage with two adjacent voltage vectors in one switching cycle. And the duty cycle of the associated voltage level is obtained by minimizing an additional cost function. This method is suitable for the cascades of n cells inverter. For reducing the computation burden and eliminating the computation delay, adjacent regions prediction method and time-delay compensation method are applied to the inverter. Finally, in this paper, the proposed strategy is applied to a single-phase grid-connected 7-level CHB inverter. Simulation and experiment are executed to show the advantages of the proposed control algorithm in dynamic state and steady state. • A double voltage vector MPC strategy is proposed for n-level CHB inverters with fixed switching frequency. • The optimal vector is composed of two voltage vectors with different action times and magnitudes in one control cycle. • The proposed method is realized to facilitate the filter design and the current THD is further improved. [ABSTRACT FROM AUTHOR]

• The original contribution of the paper is a dq-real domain admittance transfer matrix model of PV-qZ systems. • The study presents some of the the two main origins of instability in multi-terminal AC grid-connected PV-qZ systems. • The study also illustrates the weakness of GNC related to stability assessment and grid partition points. Photovoltaic (PV) power systems are becoming one of the most popular green power systems. Power converters are used in these systems. Among them, quasi-Z-source inverters (qZSIs) are currently on the rise. However, instabilities can appear in multi-terminal AC grid-connected power electronics, such as PV power systems, due to the interaction between power electronic controls and the grid. Modeling of qZSI-based PV power systems is lacking in the literature and stability assessment of grid-connected qZSI-based PV power systems is not yet well understood. Accordingly, the present paper contributes with an s -domain dq -real admittance transfer matrix model of qZSI-based PV power systems derived from their small-signal state-space averaged model. The paper also describes a systematic procedure to study multi-terminal AC grid-connected qZSI-based PV power systems by the nodal admittance method, where the proposed qZSI-based PV power system model is incorporated into the nodal admittance matrix to study stability concerns. Thus, AC grid dynamics in the presence of qZSI-based PV power systems can be investigated using impedance-based stability criteria. The proposed model and the procedure are applied in a stability study of two applications where solutions for improving stability issues are presented. In these applications, the two main causes of instabilities in AC-grid connected PV-qZ systems are analyzed in detail. The study is validated by PSCAD/EMTDC simulation.. [ABSTRACT FROM AUTHOR]

• A mathematical model for inverters' connection transients in weak and strong grids. • An improvement of transients using a phase limiter algorithm. • A set of experiments which validates the proposal. • Analysis of virtual impedance and measurement filter dynamics. This paper derives a mathematical model suitable for analysis of connection behavior of the inverter-based grids and, using that model, it presents guidelines to control grid-forming inverters' rate of change in frequency as function of output power (virtual inertia), or in other words "measured power filters". Furthermore, in order to improve the transient response, an angle difference limiter control is proposed. An angle difference limiter is a control algorithm which is constantly checking the angle difference between the inverter and the grid in the connection point limiting power peaks during the transients. The performance of the angle difference limiter is analyzed in detail and validated with an experimental microgrid consisting of two three-phase inverters and a variable load. The paper analyzes the connection of inverters in weak and strong grids validating the performance of the proposed angle difference limiter. [ABSTRACT FROM AUTHOR]

Since the observed angle of a phase-locked loop (PLL) is relatively accurate even under distorted grid conditions, the mathematical model of the voltage errors caused by the switching modulation and the dead-time effect are derived as a function of the grid voltage angle in this paper. Based on the model analysis, an adaptive compensation algorithm is proposed to suppress the grid-side current harmonics in three-phase converters. The proposed algorithm fits the unmeasurable voltage errors by a truncated Fourier series expansion, and then takes it as an equivalent disturbance in the current control loop to achieve harmonic compensation. By the feed-forward compensation, the design and tuning of the controller parameters are simplified and separated from the dynamic performance. In addition, the controller can adapt to the grid frequency variation by updating the grid voltage angle with the PLL block. To reduce the computational burden, a simplified version of the proposed method is also presented. Simulation and experiment results show that the proposed methods can suppress the current harmonics and achieve better performance in terms of total harmonic distortion, strong robustness and insensitivity to the grid frequency variations, compared with the traditional PI control or repetitive control strategy. [Display omitted] • A PI controller is designed to ensure satisfactory dynamic performance. • An adaptive method is employed to compensate the voltage errors caused by the switching modulation and the deadtime effect so as to suppress the grid current harmonics. • A simplified adaptive strategy is also presented to reduce the computational burden and the complexity to half of the original method. • The adaptive algorithm is less model-dependent and built based on the grid voltage angle with a PLL to achieve frequency adaption. [ABSTRACT FROM AUTHOR]

• The impact of distributed capacitance is eliminated due to the capacitance current can be ignored at the low frequency. • The low-frequency components only exist between the BES and the fault point, and will not flow to the opposite grid. • The least square algorithm is employed to solve the overdetermined equations, improving the accuracy of calculation. The fault current of the photovoltaic (PV)/battery energy storage (BES) hybrid power generation system contains harmonic components, which might cause the maloperation of the distance relay. The time-domain distance protection has attracted more attention recently. However, the distributed capacitance of long transmission lines negatively affects the performance of time-domain distance protection, which hinders its application. To solve this problem, this paper proposes an improved time-domain distance protection based on fault active control. By leveraging the fault active control capability of the BES inverter, a specific low-frequency characteristic voltage is modulated through the phase-locked loop (PLL). By injecting the low-frequency characteristic voltage, the influence of line distributed capacitance can be ignored. Thus, the accuracy of time-domain distance protection based on the equivalent R-L model of transmission lines is guaranteed, which is the first advantage of injecting the low-frequency characteristic voltage. The other advantage is the low-frequency components only exist between the BES and the fault point, and will not flow to the grid on the opposite side of the line. The accuracy of time-domain distance protection has been further improved. In Addition, the faulty line's derivative equations for different fault types are deduced based on fault active control. Finally, the least square algorithm is used to calculate fault distance. The proposed scheme's feasibility and effectiveness are verified through simulations in PSCAD/EMTDC. [ABSTRACT FROM AUTHOR]

With the significant trend towards variable frequency in heating ventilating and air-conditioner (HVAC) loads, the inverter-based air conditioner load (IACL) clusters are poised to become the mainstay in participating in demand response (DR). During the process of DR, once the indoor temperature exceeds the comfort constraint, HVAC load must be forced to exit DR, which brings correlation to the behaviour of the preceding and following periods, making cluster optimization modelling and solution difficult. In order to solve the problems, this paper proposes an analogue ON/OFF state-switching (AOSS) control method suitable for IACL cluster participating in DR. Firstly, the critical working point corresponding to the comfort constraint is analysed for eliminating the temporal coupling for IACL. Then, an AOSS control method is proposed based on the critical point analysis. The feasibility of the proposed AOSS control is validated by the experimental results, with the Hisense KFR-75W/T08SBp-A2 inverter-based air conditioning DR experimental platform. Furthermore, by using the proposed AOSS control, a day-ahead scheduling model is constructed, and, the traditional state-queuing (SQ) model is transplanted to the IACL cluster for short-term power control. And the case studies verified the effectiveness and applicability of the day-ahead scheduling model and the transplanted SQ model. • Analysing the critical working point corresponding to the comfort constraint. • AOSS control is proposed to eliminate the temporal coupling for IACL. • Aggregation and optimal dispatching for IACL cluster in day-ahead time scale. • Ultra-short time scale IACL cluster power control. [ABSTRACT FROM AUTHOR]

In this paper, the hybrid synchronization based grid forming (HS-GFM) control and coordination strategy are proposed for the inverter and boost converter to provide frequency support. As the main contribution, the inertia power and damping power are designed with HS-GFM based coordination strategy between inverter and boost converter. The inertia power can be obtained from DC capacitor and photovoltaic system in deloading mode independently. Besides, the damping power can be realized from the PV inverter in deloading mode. After that, the small signal models of inverter and boost converter considering grid frequency coupling are constructed with simplified single input single output (SISO) model to guide the parameter selection. Further, the grid synchronization stability, synchronization bandwidth and grid strength influence on the frequency response of the PV inverter can be analyzed with SISO model. Compared with conventional DC voltage based GFM, HS-GFM can improve stability especially in strong grid with slight reduction of synchronization bandwidth while it has the risk of instability in weak grid if parameters are not proper. Compared with phase locked loop (PLL) based control, the proposed HS-GFM control achieves a fast response under frequency excursion with better stability in weak grid. Finally, realtime and offline simulations are carried out to verify the proposed strategy and analysis. • Inertia and damping power are designed with hybrid synchronization based GFM control. • The DC side thevenin equivalence of boost converter is obtained for SISO analysis. • SISO model of PV inverter is built for stability analysis and parameter selection. • Comparisons with conventional GFM and phase locked loop based control are presented. [ABSTRACT FROM AUTHOR]

• Study of PV power plant with quasi-Z-source cascaded H-bridge multilevel inverter under failure. • Control system to provide a suitable DC voltage at the input of the VSI and ensure the grid power delivery. • Control tested from simulation results under different operating conditions and HIL experimental results. • Correct response of the developed control strategy with failure in qZSI module. At the present time, quasi-Z-source cascaded H-bridge multilevel inverters (qZS-CHBMLI) have gained attention in photovoltaic (PV) applications, due to their advantages over traditional multilevel inverters. They allow single-stage power conversion of a PV power plant by independently adjusting the DC voltage in each module; thus, each PV array operates at the maximum power. This advantage permits dispensing with a DC/DC boost converter and reduces the number of modules required. This paper develops a novel control strategy for a qZS-CHBMLI connected to a single-phase system that guarantees proper operation when a fault occurs in a quasi-impedance source inverter (qZSI). The control strategy is employed in a grid-connected qZS-CHBMLI with three modules, each one with a quasi-impedance network, a 4.8 kW PV array and a voltage source inverter (VSI), with H-bridge topology. The purpose of the control system is to deliver a suitable DC voltage at the input of the VSI and ensure the grid power requirements after a fault in a module. The proposed control system is evaluated through a 40 s simulation in MATLAB/Simulink® in two cases: A) analysis of the system behaviour when there is a variation in the operation limit equation; and B) evaluation of the control strategy under dissimilar operating conditions. In addition, an experimental setup based on an OPAL RT-4510 unit and a dSPACE MicroLabBox prototyping unit is employed to validate the results. The results confirmed the correct response of the applied strategy with the failure of a single module. [ABSTRACT FROM AUTHOR]

• A power-decoupled current source inverter (PD-CSI) is proposed for the operation in an unbalanced grid to reduce the current rating of the DC-link inductor. • A model predictive control is proposed for the PD-CSI. It achieves high performance in both stability and rapidity. • A space vector pulse width modulation is proposed for the PD-CSI. It helps to reduce the voltage rating of the ripple storage capacitor. The current source inverter (CSI) is a promising interface between the Photovoltaic (PV) panel and the three-phase AC grid. It boosts the PV panel voltage by a DC-link inductor and converts the maximum available PV power. In an unbalanced grid, double-line-frequency pulsating powers will be generated in the CSI, increasing the rating of the DC-link inductor and impeding the maximum power point tracking (MPPT) operation. To address this issue, a power decoupling (PD) circuit for a three-phase CSI is proposed in this paper. By using the DC-link inductor and active switches multiplex, the proposed PD circuit can reduce the current rating of the DC-link inductor with fewer active switches, and no detrimental power components are introduced to the utility grid. Moreover, to concurrently control multiple objectives without multiple loops, a model predictive control (MPC) method is further proposed for the PD-CSI, achieving a rapid response of PD-CSI. Besides, a space vector pulse width modulation (SVPWM) method is proposed for the PD-CSI to enhance the utilization of DC voltage, helping to reduce the voltage stress of the ripple storage capacitor. The priorities of the proposed topology and the corresponding control and modulation methods are finally verified by comparative experimental results. [ABSTRACT FROM AUTHOR]

Abstract In this paper, the system of the Linear Induction Motor (LIM) driven by direct AC–AC matrix converter is presented and its dynamic performance is briefly compared with the conventional LIM drives based on AC–DC–AC converter. Space-vector pulse-width modulation (SVM) and indirect field oriented control (IFOC) are applied to control the two employed converters. For the sake of comparison, the PI controllers are applied to control the primary (mover) speed and current considering the same parameter settings. The objective of this paper was to compare theoretically the dynamic performance of linear induction motor (single-sided LIM) drives driven by three-phase voltage source inverters and the direct AC/AC matrix converters. The study compares the dynamic performance in addition to the harmonics content and THD of the input and output voltage and current for both converters. The simulation of each system has been implemented using the MATLAB/SIMULINK platform. [ABSTRACT FROM AUTHOR]

In the current paper, an improved control strategy designed for synchronizing and transferring autonomous microgrids (MGs) to the grid is presented. The proposed approach is based on an MG leading inverter (MGLI) supplied by a supercapacitor energy storage system, which takes over the MG only during a transitory load and distributes it to the available MG supporting inverters (MGSIs). This paper presents the control systems for both the proposed MGLI and the associated MGSIs, the focus being on the specific issues related to MG synchronization and grid transfer. By means of the proposed solution, the operation of the MG and its transition between autonomous and grid-connected modes require merely the adaptation of the MGLI control system, while the MGSIs operation remain unchanged during all MG states. The comprehensive experimental results, which were carried out on a laboratory-scale MG, have shown that the system is kept stable and with minimum disturbance to the local MG voltage and frequency during the analysed events, namely the scheduled MG transfer to the grid, power-flow control during grid-connection operation, and disconnection from the grid, respectively. [ABSTRACT FROM AUTHOR]

Due to their run-time reconfigurability, short time-to-market, and lower prototype costs, FPGAs have become increasingly popular since their introduction. They found use in a wide variety of applications, including high-performance computing. However, when compared to ASICs, FPGAs offer lower performance, and they are power-hungry devices with low energy-efficiency. The emergence of Approximate Computing (AxC) represents a significant advancement in terms of enabling technology when applied to FPGA-based computing platforms. It has been effectively exploited in several application fields, achieving significant savings in energy and latency through a selective degradation of the output quality. Nevertheless, a generalized and systematic methodology for FPGA-based circuit design is still lacking. Indeed, most of the methods target ASIC-based systems, and, consequently, they offer minimal advantages or even an increase in resources when synthesized for FPGAs due to the architectural differences between the technologies. In this paper, we attempt to address this shortcoming by introducing our method for designing combinational logic circuits. It is based on and-inverter graph rewriting and multi-objective optimization, aiming for optimal trade-offs between quality of results and hardware overhead. Extensive experimental campaigns empirically prove that both generic logic and arithmetic circuits benefit from this approach. [ABSTRACT FROM AUTHOR]

The increasing penetration of renewable energy systems into the global energy matrix is a necessity for sustainable development. The benefits impact the well-being of humanity and the environment directly. However, these power generation systems demand reliable controllers to regulate the current injection into the electrical grid. Therefore, this paper presents a smart parametrisation for a robust adaptive proportional integral controller applied to grid-injected current control of a voltage inverter source with an LCL filter. Controller parameter optimisation and the initialisation of their gains are performed using the particle swarm optimisation algorithm. Three cost functions are assessed on controller parametrisation, considering the current tracking error minimisation and control action limitations: integral of absolute error (IAE) + integral of absolute control action (IAU), integral of square error (ISE) + IAU, and integral of the time-weighted absolute error (ITAE) + IAU. A framework for performance analysis and an in-depth discussion are presented, providing a systematic decision-support methodology for controller configuration. The function determined as the best one is implemented experimentally and compared with a designer's experience-based robust adaptive proportional integral controller using a hardware-in-the-loop test bench, where the improvements in controller performance are corroborated, contributing to the enhancement of energy quality in renewable energy systems. In addition, the controller's robustness is evaluated on a weak grid and an uttermost weak grid, where it presents high robustness and global stability. [ABSTRACT FROM AUTHOR]

This paper proposes a novel, passive-based anti-islanding method for both inverter and synchronous machine-based distributed generation (DG) units. Unfortunately, when the active/reactive power mismatches are near to zero, majority of the passive anti-islanding methods cannot detect the islanding situation, correctly. This study introduces a new islanding detection method based on exponentially damped signal estimation method. The proposed method uses adaptive identifier method for estimating of the frequency deviation of the point of common coupling (PCC) link as a target signal that can detect the islanding condition with near-zero active power imbalance. Main advantage of the adaptive identifier method over other signal estimation methods is its small sampling window. In this paper, the adaptive identifier based islanding detection method introduces a new detection index entitled decision signal by estimating of oscillation frequency of the PCC frequency and can detect islanding conditions, properly. In islanding conditions, oscillations frequency of PCC frequency reach to zero, thus threshold setting for decision signal is not a tedious job. The non-islanding transient events, which can cause a significant deviation in the PCC frequency are considered in simulations. These events include different types of faults, load changes, capacitor bank switching, and motor starting. Further, for islanding events, the capability of the proposed islanding detection method is verified by near-to-zero active power mismatches. [ABSTRACT FROM AUTHOR]

As a main driving force of electric vehicles (EVs), the losses of in-wheel permanent-magnet synchronous motor (PMSM) direct drive system can seriously affect the energy consumption of EVs. This paper proposes a loss optimization control strategy for in-wheel PMSM direct drive system of EVs which optimizes the losses of both the PMSM and the inverter. The proposed method adjusts the copper losses and iron losses by identifying the optimal flux-weakening current, which results in the PMSM achieving the lower losses in the whole operational range. Moreover there are strongly nonlinear characteristics for the power devices, this paper creates a nonlinear loss model for three-phase half-bridge inverters to obtain accurate inverter losses under space vector pulse width modulation (SVPWM). Based on the inverter loss model and double Fourier integral analysis theory, the PWM frequency is optimized by the control strategy in order to maximize the inverter efficiency without affecting the operational stability of the drive. The proposed loss optimization control strategy can quickly find the optimum flux-weakening current and PWM frequency, and as a result, significantly broaden the high efficiency area of the PMSM direct drive system. The effects of the aforementioned strategy are verified by both theoretical analysis and experimental results. [ABSTRACT FROM AUTHOR]

In recent past, numerous multilevel architectures came into existence. In this background, cascaded multilevel inverter (CMLI) is the promising structure. This type of multilevel inverters synthesizes a medium voltage output based on a series connection of power cells which use standard low-voltage component configurations. This characteristic allows one to achieve high-quality output voltage and current waveforms. However, when the number of levels increases switching components and the count of dc sources are also increased. This issue became a key motivation for the present paper. The present paper is devoted to investigate different types of CMLI which use less number of switching components and dc sources and finally proposed a new version of Multi-cell based CMLI. In order to verify the proposed topology, MATLAB – simulations and hardware verifications are carried out and results are presented. [ABSTRACT FROM AUTHOR]

In this paper theoretical and experimental analysis of an AC–DC–AC inverter under DC link capacitor failure is presented. The failure study conducted for this paper is the open circuit of the DC link capacitor. The presented analysis incorporates the results for both single and three phase AC input. It has been observed that the higher ripple frequency provides better ride through capability for this fault. Furthermore, the effects of this fault on electrical characteristics of AC–DC–AC inverter and mechanical properties of the induction motor are also presented. Moreover, the effect of pulsating torque as a result of an open circuited DC link capacitor is also taken into consideration. Theoretical analysis is supported by computer aided simulation as well as with a real time experimental prototype. [ABSTRACT FROM AUTHOR]

Voltage unbalance is a major yet often overlooked power quality problem in low voltage residential feeders due to the random location and rating of single-phase renewable sources and uneven distribution of household loads. This paper proposes a new indicator of voltage deviation that may serve as a basis of analysis and compensation methods in this dimension of power quality. The paper proposes three main results. First of all a novel voltage norm capable of jointly indicating unbalance and under-voltage in a single value, afterwards a three phase unbalance reduction controller structure is given. As the third main result, the proposed controller structure is integrated with an optimization based control algorithm that uses asynchronous parallel pattern search as its engine. The suggested structure and the underlying three phase power grid model has been implemented in a dynamical simulation environment and tested against engineering expectations. The simulation based experiments served as a proof of concept for the proposed complex control structure. The experiments included performance and robustness analysis, both of them concluded that the proposed control and inverter structure is promising. The proposed three phase inverter structure together with the control algorithm connected with a renewable source (photovoltaic panel or wind turbine) is capable of an asymmetric power injection or rerouting the energy flow to the grid so that the voltage unbalance decrease. This is also important from the environmental point of view since the achieved power loss reduction can easily be translated to CO 2 emission reduction and carbon footprint - these indicators has also been calculated. [ABSTRACT FROM AUTHOR]

• Causes of premature delamination in the power module for new energy vehicles were systematically studied. • Over-corrosion on the copper strip surface in the pickling process was the root cause. • Overlapping skins on the copper bridge surface in the stamping process were another root cause. For the inverter in the new energy vehicle, the existence of the power module provides it have the function of converting direct current (DC) in the battery pack into three-phase alternating current (AC) driving the motor. Therefore, the reliability of the power module is significant to ensure the stable operation of vehicles. In this paper, a failure case about premature delamination between the copper bridge and epoxy molding compound (EMC) in the power module during power cycling tests was reported. To find out the causes of premature delamination, a series of characterization methods including thermogravimetric analysis (TGA), inductively coupled plasma-mass spectrometry (ICP-MS), ion chromatography (IC), three-dimensional stereo microscope (3D-SM), metallurgical microscope (MM), scanning electron microscope (SEM) and energy dispersive spectrometer (EDS) were adopted. The analysis objects contained the EMC, circulating water, copper strips in different stages, copper bridges and decapped power modules, which were all covered in the manufacturing process of power modules. By comprehensive analysis, over-corrosion on the copper strip surface and overlapping skins on the copper bridge surface were determined as the root causes of premature delamination. Based on the conclusions, corresponding countermeasures were also proposed. This paper gives a kind of pre-analysis method to the possible failure of the components, so it is meaningful for how to effectively prevent the failure of the components during assembly process. [ABSTRACT FROM AUTHOR]

This paper introduces a new HT-type module for both symmetrical and asymmetrical multilevel inverters (MLIs) with reduced power electric components. The proposed module comprises of two back to back T-type inverters connected with four cross-connected switches. This MLI addresses two major drawbacks associated with the conventional and other recently proposed MLIs which are the high voltage stress of switches and higher power component counts. The structure of the proposed device is designed combining the beneficial features of both T-type inverter and cross-switched inverter. The 1st feature allows the module to produce negative voltage levels deprived of any extra H-bridge circuit and thus decreasing the overall voltage stress significantly. The latter feature allows the device to utilize reduced number of switches to produce higher voltage levels. A comprehensive comparative analysis is additionally established between other MLI topologies to confirm the superiority of the HT-type MLI. From this analysis, it is found that the proposed MLI has successfully overcome the issues associated with other MLIs, it was able to produce the results following industrial standards and it outperformed other MLIs in different aspects such as power components count, cost, efficiency and dynamic performance. Selective harmonic elimination pulse width modulation (SHE-PWM) and nearest level control (NLC) algorithm is considered in this manuscript to generate the output results from the proposed HT-type module. All the details about the operating principle and modulation techniques utilized for the proposed MLI module are stated and validated by both simulation and experimental results. [ABSTRACT FROM AUTHOR]

Solar Photovoltaic (SPV) inverters have made significant advancements across multiple domains, including the booming area of research in single-stage boosting inverter (SSBI) PV scheme. This article comprehensively covers four critical components of the system, namely boosting topologies, voltage and current control methods, Maximum Power Point Tracking (MPPT) methods, and grid synchronization. It conducts thorough analysis and comparisons of various topologies in terms of their performance, cost, volume, lifetime, and grid interfacing requirements for a 200 W reference power level. Furthermore, it investigates the advantages and disadvantages of single-phase inverter control methods and synchronization methods. The MPPT techniques are evaluated based on complexity, robustness, and precision. This paper presents an outline of the series-connected Low Voltage AC (LVAC) scheme, along with several potential areas for further study. By providing insightful analysis and development ideas, this article equips researchers to design and develop optimized single-stage PV systems with increased efficiency and effectiveness. [ABSTRACT FROM AUTHOR]

This paper focuses on the problem of voltage control of islanded inverter-interfaced microgrids consisting of several distributed generation (DG) units with radial structure. The main objectives are to (i) design a decentralized/distributed voltage controller with minimum information exchange between DG units and their local controllers (ii) design a fixed-/low-order dynamic output feedback controller which ensures stability as well as desired performance of the microgrid system in spite of load parameter uncertainties. To this end, the problem is formulated as an optimization problem which is the minimization of the cardinality of a pattern matrix subject to an H ∞ performance constraint. Since the problem is intrinsically non-convex, a convex optimization-based design procedure for the controller synthesis is proposed in this paper. The effectiveness of the proposed controller is evaluated through simulation studies and Hardware-In-the-Loop (HIL) verifications. The simulation and experimental results demonstrate the effectiveness of the proposed control strategy. [ABSTRACT FROM AUTHOR]

This paper presents an indirect rotor-flux-oriented (IRFO) control system of the self-excited induction generator (SEIG) in which excitation is achieved by means of a current-controlled voltage source inverter (CC-VSI) and a single electrolytic capacitor. In the proposed control scheme, both the iron losses and the magnetic saturation are taken into account and calculated online. The main objective is to keep the DC voltage across the capacitor constant and equal to the reference value, regardless of changes in the rotor speed and load. The study is mainly focused on the DC voltage control and, more specifically, on selection of the appropriate DC voltage controller. Besides considering widely accepted types of controllers, i.e., the classical PI controller and the fuzzy logic (FL) controller, this paper proposes an alternative solution – a new type of DC voltage controller based on hedge algebra. To our best knowledge, this is the first time that such a controller is considered for application in electrical engineering. The performance of the developed hedge algebra (HA) controller is evaluated through comparison with the optimal-tuned classical PI controller and the Sugeno-type FL controller. The simulation and experimental analysis are carried out in reasonably wide ranges of the DC voltage, load and rotor speed, including the case of a variable rotor speed. It is shown that the proposed HA controller provides superior performance in terms of tracking the reference DC voltage value as well as robustness to speed and load disturbances in the system. [ABSTRACT FROM AUTHOR]

• The controller has inherent robustness against the LCL filter resonance and thus removes the need for PD, which produces losses, or AD, which increases the total cost of the system due to the need for extra sensors. • By selecting the controller parameter with a sensitivity analysis over the open-loop transfer function, the closed-loop system shows sufficiently high stability margins. First, the formulation of the open-loop and closed-loop functions is given. • The analysis of the closed-loop transfer function shows the stability of the closed-loop system against the LCL filter inductance and capacitance variations. • The control law is parameterized based on the future reference trajectory over the control and prediction horizons to deal with the steady-state offsets. The approach for the prediction of the future reference trajectory is discussed. • The optimization routine is performed offline, and the control law can easily be implemented in low-cost processors. • To control the power factor precisely, the grid-side currents are selected as the control variables. This paper presents a Generalized Model Predictive Control (GPC) in the natural reference frame for a 3-phase LCL-filter based grid-tied inverter. The proposed controller can track the sinusoidal reference without steady-state phase and amplitude offsets. This is achieved by parameterizing the control law matrices with considering the future reference trajectory. To cope with the LCL filter resonance, traditional controllers need a damping method. The proposed controller has inherent damping against the LCL filter resonance and extra sensors are avoided. The controller parameters are selected by a sensitivity analysis that guarantees the closed-loop stability. The proposed controller provides high accuracy in controlling active and reactive currents, robustness against grid inductance variations, low real-time computation, and a fixed switching frequency. The simulation and experimental results prove the performance of the controller in tracking the grid-side reference currents. [ABSTRACT FROM AUTHOR]

• A generalized control strategy (composed of finite set model predictive control with delay compensation and inverse dynamic model control) is proposed, which improves the equivalent output impedance and phase margin of inverters. • The proposed control strategy can achieve order reduction of inverter's control system, which suppresses the resonance peak of the system and further improves the stability of multi-inverter parallel system. • The high robustness against various parameters of the proposed strategy have been proven through Lyapunov stability and frequency domain analysis. • The proposed control strategy can ensure that the THD value of grid connected current is less than 5% under very weak grid condition and other situations. Under weak-grid condition, the mismatch degree between grid impedance and inverter output impedance can increase, which will lead to inverter instability. Compared with conventional power grid, the parallel resonance of multi-inverter parallel system is more likely to happen. In order to improve inverter stability and suppress multiple-inverter parallel resonance under weak-grid condition, a new generalized control mode for control layer is proposed in this paper, which is based on finite set model predictive control (FCS-MPC) and inverse dynamic model control (IDM). The FCS-MPC with delay compensation is introduced into the current inner loop of the control layer, and the IDM control is introduced into the voltage outer loop, so as to make the transfer functions of current inner loop and voltage outer loop unitized and further reduce the order of the inverter's control system. Order reduction can improve the phase margin of the inverter output impedance, in other words, enhance inverter dynamic performance. Finally, the simulation model of multi-inverter parallel system is built, and by comparing with the traditional control strategies, the effectiveness of the proposed control strategy is verified. [ABSTRACT FROM AUTHOR]

• Study of microgrid with energy-stored quasi-Z-source cascaded H-bridge multilevel inverter and PV system. • Development of energy management system based on model predictive control (MPC-EMS). • Results compared with proportional sharing algorithm based on SOC level (SOC-EMS). • Best results obtained from MPC-EMS. This paper presents a new energy management system (EMS) based on model predictive control (MPC) for a microgrid with solar photovoltaic (PV) power plants and a quasi-Z-source cascaded H-bridge multilevel inverter that integrates an energy storage system (ES-qZS-CHBMLI). The system comprises three modules, each with a PV power plant, quasi-impedance network, battery energy storage system (BESS), and voltage source inverter (VSI). Traditional EMS methods focus on distributing the power among the BESSs to balance their state of charge (SOC), operating in charging or discharging mode. The proposed MPC-EMS carries out a multi-objective control for an ES-qZS-CHBMLI topology, which allows an optimized BESS power distribution while meeting the system operator requirements. It prioritizes the charge of the BESS with the lowest SOC and the discharge of the BESS with the highest SOC. Thus, both modes can coexist simultaneously, while ensuring decoupled power control. The MPC-EMS proposed herein is compared with a proportional sharing algorithm based on SOC (SOC-EMS) that pursues the same objectives. The simulation results show an improvement in the control of the power delivered to the grid. The Integral Time Absolute Error, ITAE, achieved with the MPC-EMS for the active and reactive power is 20 % and 4 %, respectively, lower than that obtained with the SOC-EMS. A 1,3 % higher charge for the BESS with the lowest SOC is also registered. Furthermore, an experimental setup based on an OPAL RT-4510 unit and a dSPACE MicroLabBox prototyping unit is implemented to validate the simulation results. [ABSTRACT FROM AUTHOR]

Abstract Due to the scaling and zero-drift of current sensor errors, unbalanced grid voltages, tolerance of power switching devices, and asymmetry of PWM gate driving pulses, transformerless grid-connected inverters usually have certain amount of dc components injected to the ac grid. Therefore, power quality of the grid is degraded. Many efforts, such as using blocking capacitors, a dc current feedback control method, and a voltage dc component feedback control method, etc., have been introduced to minimize the dc injection. This paper proposes an intelligent control strategy of dc current injection suppression to the grid by utilizing adaptive-back-propagation (ABP) neural network PID controller. The performance of the proposed scheme is evaluated and compared with the traditional and existing method. Finally, the control scheme is verified on a 2-kW three-phase grid-connected inverter in the laboratory. Highlights • Analyze the sources that may lead to dc current in a grid-connected inverter. • Adaptive BP neural work based PID control is proposed to minimize the dc current. • Learning coefficients of adaptive BP-PID controller are on-line regulated. • Propose sliding window double integration method for dc current extraction. [ABSTRACT FROM AUTHOR]

Highlights • We model the system with the Semi-Markov process theory and the renewal point technique. • A efficient algorithm based on set partition method is presented. • The transient and the steady-state reliability indices are explicitly obtained. • The steady-state availability is unrelated with arbitrary initial condition is demonstrated. Abstract With the shortage of nonrenewable energy, renewable energy resources play an important role in practice. One of the most promising renewable energy is viewed as solar energy resources due to its cleanliness and the inexhaustibility. However, the quantitative assessment method on the reliability of a complicated solar energy generating system has been a considerable challenge. In this paper, we propose a Markov model to imitate a solar energy generating system with inverters in series, unreliable by-pass change-over switches, and common cause failure. Employing the renewal point technique and the Semi-Markov process theory, we build the quantitative reliability models of the system. Further, we develop a new algorithm to obtain the explicit form solution of reliability indices. An example illustrates that the proposed models and the algorithm are efficient and concise. [ABSTRACT FROM AUTHOR]

• A comprehensive survey on control strategies of DGPSs is reviewed. • Several PNS extractors have been presented to produce the signals required for RCG. • The theoretical and comparison assessment of RCG based control strategies are discussed. • Advanced control strategies are overviewed to overcome power quality problems. High energy demand, low cost requirements and higher reliability requirements increase the importance of distributed generation power systems (DGPSs). The large capacity DGPSs requires high performance control algorithms and synchronization techniques based positive-negative sequence (PNS) extractors to fulfil system reliability and power quality requirements under not only during normal operating conditions, but also under unbalanced grid conditions. The power quality problems caused by voltage unbalances, voltage sag/swell, voltage fluctuations, phase faults and harmonic distortions have critical influences on control of power converter devices interfaced DGPSs. In literature studies, novel control strategies with phase locked loops (PLLs) techniques based PNS extractors are used to overcome these problems. In this paper, a comprehensive review on various advanced control strategies and PNS extractors for interlinking three phase inverter in the DGPSs are comprehensively investigated and discussed under normal and abnormal conditions. Several PNS extractors have been overviewed to produce the sequences components required for reference current generation (RCG). The theoretical assessment of the RCG based flexible control strategies and overcurrent limitation control are also comprehensively analysed, surveyed and compared in detail to deal with power quality problems. Comparative analyses for PNS extractors, voltage/current regulation controllers and RCG based control strategies have been detailed presented and analysed. The presented detailed overview can be useful to researchers studying impact of normal and abnormal conditions on various control strategies with or without any using PLLs based PNS extractors for three-phase inverters interfaced DGPSs. [ABSTRACT FROM AUTHOR]

Abstract Recently, LCL filters have been widely used in the output of single phase inverters. Since, the grid side inductor in these filters is in series with the grid impedance at the Point of Common Coupling (PCC), it may create new resonances. This phenomena may take the control loop toward instability. In this case, in order to have a reliable operation, the current controller should be insensitive to the grid impedance variation. In order to damp these resonances, researchers have presented some methods using active or passive damping. These methods added an extra loop to the control loop, an extra passive component in the filter or extra sensor in the control process. But in most of them, the complexity and the cost of controller have been increased. Therefore, presenting a simple control method without extra sensor, passive component or extra arrangement can be a promising approach. This paper presents an MPC-based current controller, which is simple and robust against the grid impedance variation and even the variation of the LCL filter parameters. In contrast to classical multi-loop controller like Proportional-Resonant (PR) controllers, the proposed control method does not need any parameter tuning. In the proposed controller, the switching plan and duty cycles are determined by a cost function and a switching table. Therefore, at the same time with any variation in grid impedance, the proposed controller changes the next switching state and duty cycle. Operating performance like look-up table, searching in all possible switching states to find the best state for the next switching period, makes the controller adaptive and robust against the variation of LCL filter parameters. In order to confirm the effectiveness of the proposed controller, simulations and experimental results of the proposed controller are compared with a classical PR controller. Highlights • An MPC-based current controlled for single phase grid connected inverters has been proposed. • The grid impedance variation and its effect on resonance of LCL filters has been discussed. • The results of the proposed controller have been compared with a classical PR controller. • The results showed that the proposed MPC method, in contrast with the PR controller, is robust when grid impedance changes. [ABSTRACT FROM AUTHOR]

Abstract LCL filter is an important component in the grid-connected inverters. The parameters of LCL filter have a strong influence on the output current distortion of inverters. For three-level inverter system, a parameters design method is proposed in this paper based on genetic algorithm optimization of output current total harmonic distortion (THD). By deducing the transfer function of the filter, output current THD is calculated through double Fourier analysis. Then an adaptive immune genetic algorithm is designed to solve the objective parameters optimization issue under constraint condition. With harmonics attenuation in both fundamental band and carrier band taken into account, the filter parameters are optimized scientifically by the global search algorithm, which contains punishment mechanism, adaptive parameters and the mechanism of immune algorithm. The feasibility of the proposed method is verified by conducting simulation and experiment. [ABSTRACT FROM AUTHOR]

Abstract In this paper, New asymmetric cascaded half H bridge multilevel inverter MLI is proposed. It is driven from the conventional asymmetric cascaded half H Bridge multilevel inverter. Thus, the proposed topology inherits its simplicity, flexibility and modularity in both construction and control. By proper choice of the input DC sources values and interconnection, proposed topology can eliminate the need for polarity generation circuit which normally associated with the cascaded half H-bridge. Therefore, reduces number of switches that require high blocking voltage. The selective harmonic elimination SHE method is applied to generate switching pattern to eliminate harmonics inherently associated with MLI. The proposed topology switching pattern naturally reduces component's voltage stress, switching losses and finally decrees MLI size and cost. Mathematical expressions and analysis have been driven as well as comparison with other topologies. The validity of the proposed topology is verified with Matlab/Simulink model and then a prototype is built and experimental results are presented. [ABSTRACT FROM AUTHOR]

Abstract The paper presents an alternative scheme using fuzzy logic methodology to control a grid-connected photovoltaic system through ZSI using MCBC method. The system model and control are implemented using MATLAB-SIMULINK simulation toolbox. In view of control, Fuzzy Logic Controllers (FLCs) are designed to enhance the system stability. To ensure a unity power factor operation, the inverter modulation index is controlled to manage the phase current of the grid. Also, the control in the shoot-through ratio controls the output voltage of the PV array, so the maximum power (MP) is extracted. The simulation results using FLCs are compared with others obtained using Proportional Integral (PI) controllers. This is under the same normal operating and transient conditions which are irradiation variation, three-phase short circuit fault at point of connection and voltage variation of the grid. The simulation results of FLCs achieve supplementary enhancement of the system stability over various operating conditions. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Coordinated control of three- and arbitrarily connected single-phase energy sources. • Accurate power flow regulation at the microgrid's point-of-common-coupling. • Unbalance compensation by single- and three-phase inverter-interfaced resources. • Active and reactive power sharing proportional to local power availabilities. • Compliance with constraints and limits of distributed energy resources. Abstract This paper proposes the third generation of the Power-Based Control, that is, an approach to effectively coordinate the operation of single- and three-phase inverter-interfaced distributed energy resources that can be arbitrarily connected among the phases of three-phase four-wire low-voltage microgrids. The aim of the approach is to precisely regulate the power exchanged with the main grid by fairly exploiting the available distributed resources while respecting their own local constraints. This allows to achieve demand-response, unbalance compensation, and improved voltage profiles, which is valuable for limiting stress conditions to the distribution infrastructure. The technique is based on a master/slave microgrid architecture where the distributed inverters act as slave units driven by a centralized master controller. This latter employs the Power-Based Control in order to steer the contribution of the inverters on the basis of the microgrid power status. In particular, active, reactive, and unbalance power terms are processed by the master controller and the corresponding microgrid's power needs shared among the distributed energy resources, to achieve the compensation target at the point-of-common-coupling with the main grid. The strategy proposed herein drives the three-phase inverters to operate balanced, which avoids unwanted voltage fluctuations at the DC-side of the inverters; instead, single-phase inverters, which can be connected arbitrarily among the phases of the distribution grid, are exploited to compensate any residual unbalances (i.e., negative- and zero-components). The control technique is analyzed and demonstrated by computer simulations considering a real urban meshed distribution network. Steady-state and dynamic results and performances are reported and discussed considering typical demand and generation profiles. [ABSTRACT FROM AUTHOR]

Abstract In this paper, a robust/adaptive perturbation observer based fractional-order sliding-mode controller (POFO-SMC) is designed for a photovoltaic (PV) inverter connected to the power grid, in which a maximum power point tracking (MPPT) based on variable step size incremental conductance (INC) technique is achieved to harvest the available maximum solar energy from the PV arrays in the presence of various atmospheric conditions. A nonlinear extended state observer (ESO), called sliding-mode state and perturbation observer (SMSPO), is used to efficiently estimate the aggregated effect of PV inverter nonlinearities and parameter uncertainties, unmodelled dynamics, stochastic fluctuation of atmospheric conditions, and external disturbances. Then, a fractional-order sliding-mode controller (FOSMC) is designed to considerably enhance the system robustness via real-time perturbation compensation and to noticeably accelerate the tracking rate compared to the traditional integer-order sliding-mode control (SMC) through employing a fractional-order proportional–derivative (FOPD) sliding surface. In addition, more reasonable control efforts could be realized since the upper bound of perturbation is replaced by its real-time estimate, such that the inherent over-conservativeness of conventional SMC can be effectively reduced. Four case studies are carried out under Matlab/Simulink environment. Simulation results verify the effectiveness and superiority of POFO-SMC compared to that of proportional–integral (PI) control, feedback linearization control (FLC), SMC, robust SMC (RSMC), and FOSMC. Finally, a dSpace based hardware-in-loop (HIL) experiment is undertaken for the purpose of implementation feasibility validation. Highlights • A perturbation observer based fractional-order sliding-mode controller is proposed. • A satisfactory MPPT of the PV system is achieved by the proposed approach. • Considerable robustness is provided against to various modelling uncertainties. • dSpace based HIL experiment validates the implementation feasibility of POFO-SMC. [ABSTRACT FROM AUTHOR]

This paper presents the design of a discrete-time control scheme for the current injected into the grid by a single-phase voltage source inverter (VSI). The VSI is connected to the grid by means of an LCL filter that attenuates the switching harmonics present in the output waveform of the inverter. The current control is based on a resonant regulator implemented in a Two-Degrees-Of-Freedom (2DOF) scheme that allows the location of all the poles to be defined in the closed loop of the system without the need for observers and measuring only the current injected into the grid. This control scheme, therefore, allows the attenuation of the resonance frequency of the LCL filter and requires no additional damping methods with which to mitigate the resonance phenomenon. The design parameters can be obtained using a fairly straightforward mathematical approach that involves only operations with real numbers. The simulation and experimental results obtained show that the control scheme performs correctly even considering changes in the grid inductance. • The current control for a single-phase inverter with an LCL filter is addressed. • A fast response and zero-tracking error is achieved. • The design methodology permits the complete definition of the closed-loop poles. • Only the grid-side current is needed for control and damping purposes. • The control stability against changes in the grid inductance is addressed. [ABSTRACT FROM AUTHOR]

In this work it is established for the first time that the internal parameters of the electrical equivalent circuit of vanadium redox flow battery (VRFB) are variable not only with flow rate and stack current but also the state of charge (SOC) and operational cycle number. The dynamic internal circuit parameters are extracted by using the charge-discharge characteristics of a practical 1 kW 6 h VRFB system as input to the proposed model. The role of temperature on the VRFB internal parameters is also discussed. It is further demonstrated that the average error in estimation of VRFB stack voltage using dynamic parameters reduces by 28% (charging) and 14% (discharging) compared to that of using static internal parameters. The proposed model exhibits robustness and validity for large scale applications as evidenced by further extracting the internal parameters of a 125 kW 2 h VRFB system. Another significant contribution of this paper is the optimization of flow rate by considering both the stack internal power loss and pump power loss simultaneously to achieve optimal performance of the VRFB system. The proposed model involving dynamic parameter extraction and loss optimization is very useful for designing suitable battery management system (BMS) for interfacing VRFB with renewable energy sources. [ABSTRACT FROM AUTHOR]

Abstract Parallel connected electrical machines drive systems have received significant attention due to their use in special purpose applications. Recently, control of such systems using a single inverter has been considered for improving stability during uneven load conditions on machines. In this paper, a synchronized control strategy for stable operation of dual parallel brushless direct current motors using a single three-phase inverter is proposed. Control of parallel connected brushless direct current motors suffers from instability under different load torques. To obtain the stability, an effective control method based on master-slave strategy is presented. To analysis the stability, the detail model of the proposed system is developed for an electric vehicle propulsion system. Therein, the motor with the highest load or with lagging rotor position is selected as the master and is directly controlled. The effectiveness of the proposed system is demonstrated by a series of case studies in different operation conditions. [ABSTRACT FROM AUTHOR]

The forecasting of the thermal power demand is essential to support the development of advanced strategies for the management of local resources on the consumer side, such as heating ventilation and air conditioning (HVAC) equipment in buildings. In this paper, a novel hybrid methodology is presented for the short-term load forecasting of HVAC thermal power demand in smart buildings based on a data-driven approach. The methodology implements an estimation of the building's activity in order to improve the dynamics responsiveness and context awareness of the demand prediction system, thus improving its accuracy by taking into account the usage pattern of the building. A dedicated activity prediction model supported by a recurrent neural network is built considering this specific indicator, which is then integrated with a power demand model built with an adaptive neuro-fuzzy inference system. Since the power demand is not directly available, an estimation method is proposed, which permits the indirect monitoring of the aggregated power consumption of the terminal units. The presented methodology is validated experimentally in terms of accuracy and performance using real data from a research building, showing that the accuracy of the power prediction can be improved when using a specialized modeling structure to estimate the building's activity. [ABSTRACT FROM AUTHOR]

The rapid developments of advanced metering infrastructure and dynamic electricity pricing provide great opportunities for residential electrical appliances, especially air conditioners (ACs), to participate in demand response (DR) programs to reduce peak power consumptions and electricity bills. One of the biggest challenges faced by residential DR participants is the lack of intelligent DR control methods which enable residential ACs to automatically respond to dynamic electricity prices. Most existing studies on DR control of residential ACs focus on single-speed ACs. However, inverter ACs which have higher part-load efficiencies have been extensively installed in today’s residential buildings. This paper presents a novel model-based DR control method for residential inverter ACs to automatically and optimally respond to day-ahead electricity prices. A control-oriented room thermal model and steady-state model of inverter ACs are developed and integrated to predict the coupled thermal response of the room and AC for the purpose of model-based control. Optimal scheduling of indoor air temperature set-points is formulated as a nonlinear programming problem which seeks the preferred trade-offs among electricity costs, thermal comfort and peak power reductions. Genetic algorithm (GA) is used to search the optimal solution of the nonlinear programming problem. Simulation results show that compared with the baseline case, the proposed model-based optimal control method can reduce the whole electricity costs and the peak power demands during DR hours while meeting thermal comfort constraints. Besides, sensitivity analyses on the trade-off weightings in the optimization objective function demonstrate that electricity costs, occupant comfort and peak power reductions are sensitive to the weightings and the use of the weightings is effective in achieving the best trade-off. [ABSTRACT FROM AUTHOR]

In this paper, a fully distributed approach is proposed for a class of virtual power plant (VPP) problems. By characterizing two specific VPP problems, we first give a comprehensive VPP formulation that maximizes the economic benefit subjected to the power balance constraint, line transmission limits and local constraints of all distributed energy resources (DERs). Then, utilizing the alternating direction method of multipliers and consensus optimization, a distributed VPP dispatch algorithm is developed for the general VPP problem. In particular, Theorem 1 is derived to show the convergence of the algorithm. The proposed algorithm is completely distributed without requiring a centralized controller, and each DER is regarded as an agent by implementing local computation and only communicates information with its neighbors to cooperatively find the globally optimal solution. The algorithm brings some advantages, such as the privacy protection and more scalability than centralized control methods. Furthermore, a new variant of the algorithm is presented for improving the convergence rate. Finally, several case studies are used to illustrate the efficiency and effectiveness of the proposed algorithms. [ABSTRACT FROM AUTHOR]

This paper presents modeling and study of 12-pulse HVDC (High Voltage Direct Current) based on real time simulation where the HVDC inverter is connected to a weak AC system. In goal to study the dynamic performance of the HVDC link, two serious kind of disturbance are applied at HVDC converters where the first one is the single phase to ground AC fault and the second one is the DC link to ground fault. The study is based on two different mode of analysis, which the first is to test the performance of the DC control and the second is focalized to study the effect of the protection function on the system behavior. This real time simulation considers the strength of the AC system to witch is connected and his relativity with the capacity of the DC link. The results obtained are validated by means of RT-lab platform using digital Real time simulator Hypersim (OP-5600), the results carried out show the effect of the DC control and the influence of the protection function to reduce the probability of commutation failures and also for helping inverter to take out from commutation failure even while the DC control fails to eliminate them. [ABSTRACT FROM AUTHOR]

One of the main challenges when designing a new self-powered Low Power Wide Area Network (LPWAN) technology is the vast operational dependence on its scarce energy resources. Therefore, a thorough identification and characterisation of the main energy consumption processes may lay the foundation for developing novel mechanisms aimed to make a more efficient use of devices’ batteries, as well as for planning future network deployments. This paper provides an analytical energy consumption model for IEEE 802.11ah WLANs, which are expected to become one of the technology drivers in the future development of the Internet of Things (IoT). Given the network characteristics, the presented analytical model is able to provide an estimation of the average energy consumed by a station in the network, predicting its battery lifetime, based on a set of closed-form equations. In addition, this model can be used as a tool to understand the effects of the main network parameters on the network energy consumption, and to find the most suitable network configuration for a given application scenario. [ABSTRACT FROM AUTHOR]

The effective design of Distributed Energy Systems (DES) is subject to multiple uncertainties related to aspects like the availability of renewable energy, the building energy demands, and the energy carrier prices. Nevertheless, current practices involve the use of deterministic design models, which overlook uncertainty and can lead to suboptimal DES configurations that fail to deliver the desired performance. A necessary condition in order to obtain robust DES designs against uncertainty is the understanding of uncertainty’s impacts and main drivers. Therefore, this paper presents a novel methodological framework for the investigation of uncertainty in the context of DES design, which combines optimisation-based DES models and techniques from Uncertainty Analysis (UA) and Global Sensitivity Analysis (GSA). Moreover, the application of the framework is illustrated with a case study for the optimal DES design of a Swiss urban neighbourhood. Embarking from a deterministic DES design model, first, all sources of uncertainty are identified and appropriate probabilistic descriptions are assigned to all uncertain model parameters. UA is then performed using Monte Carlo (MC) simulations to quantify the impacts of uncertainty. Results reveal substantial variations in terms of economic and carbon performance of the optimal DES, but also in terms of optimal DES configurations. Moreover, the UA results indicate that the optimal system costs are mostly higher than the deterministic cost estimates, while the inverse is observed for the case of carbon emissions. Additionally, in many of the MC simulations, the resulting optimal DES configurations deviate significantly from the deterministically obtained designs, which confirms the risk of suboptimal decisions in deterministic design processes. Moreover, the results of UA can function as decision support by identifying the DES configurations that are optimal for most realisations of uncertainty. Finally, to identify the uncertain parameters that are mostly responsible for the variation of the economic performance of the DES, a two-step GSA is launched, combining the Morris method and the variance-based Sobol method. Results of the GSA indicate the energy demand patterns and the energy carrier prices as primarily responsible for the variability of the optimal system cost, while parameters like the investment costs and the technical characteristics of the technologies exert only minimal influence. The results of GSA, besides offering a better understanding of uncertainty to DES designers, also identify the parameters for which additional effort needs to be invested to reduce their uncertainty and, as a result, the uncertainty associated with DES design. [ABSTRACT FROM AUTHOR]

Grid-connected inverters with LCL filters need high steady-state control accuracy, fast dynamic response performance, and strong robustness to guarantee the power quality. However, there are many problems in traditional control strategies that restrict improvements to control system performance, such as poor dynamic performance of traditional single-repetitive control, large ripples, low steady-state accuracy of inverter current feedback based repetitive dual-loop control or grid-current feedback based single-loop proportional-integral control. In this paper, a novel dual closed-loop repetitive control strategy based on grid current feedback is proposed for single-phase grid-connected inverters with LCL filters. The proportional-integral inner loop is stabilized by using an inherent one-beat delay achieved by digital controller. Based on the inner loop system, a detailed design scheme of a repetitive controller is presented, through which direct control of the grid current is realized, the reference is tracked perfectly to a zero phase shift, and high-attenuation gain is achieved in the high frequency range. In particular, the gird-voltage feed forward control and current reference feedforward control are adopted to suppress grid-voltage disturbance and increase dynamic tracking performance. Finally, the simulation and experimental results show that the proposed method has the advantages of high steady-state accuracy, fast dynamic response, and anti-disturbance ability. [ABSTRACT FROM AUTHOR]

The large-scale application of renewable energy is promising to solve the energy crisis over the world. Renewable energy is generally integrated into distribution networks or microgrids through inverters. Inverter-interfaced distributed generators (IIDGs) have the advantage of utilizing renewable energy effectively and flexibly. However, the wide interconnection of IIDGs causes transient stability to the public grid. This paper presents the transient stability mechanism of the grid-connected IIDGs using droop control. The transient stability mechanism is obtained by combining the transient stability condition and the comprehensive dynamic trace. The transient stability condition is proposed by the transient model and IIDGs’ operation features. The comprehensive dynamic trace is formulated by the active and reactive power curves during transient events. The mechanism is able to reflect the relations between transient stability and droop factors and reveal the transient behaviors of IIDGs. The transient stability judgment is correspondingly developed. A series of simulations demonstrate the correctness and effectiveness of the transient stability mechanism. The transient stability mechanism better expands and develops the utilization of renewable energy. [ABSTRACT FROM AUTHOR]

According to the recently proposed concept of PV-STATCOM that utilizes photovoltaic (PV) inverter as STATCOM, PV solar farm plays an increasingly important role in providing fast reactive power compensation, especially during the voltage recovery processes under voltage sag or post-fault conditions. To relieve the enormous economic losses caused by the inefficiency in voltage recovery scenario, the reactive power fast response characteristic of PV should be adequately considered in optimal siting and sizing of distributed generation. In this paper, a weighted voltage support ability index (WVSAI) based on sensitivity analysis has been firstly used to quantify the influence of PV-STATCOM on voltage recovery efficiency under voltage sag or post-fault conditions. With the WVSAI added to traditional distributed generator (DG) planning constraints, a modified optimal siting and sizing model is proposed for the targets of minimizing the total annual cost associated with the DGs to be planned. The proposed model is classified into the type of mixed integer nonlinear programming (MINLP) and then relaxed by second order cone programming (SOCP). After relaxation, commercial solver CPLEX through YALMIP platform is used to solve the relaxed model. The proposed model has been applied in IEEE 33-bus distribution system under scenarios with different WVSAI restrictions. Based on the optimal solutions of DGs’ siting and sizing, PSCAD simulation tool is used to emulate voltage recovery processes of a specific sensitive load under voltage sag, and thus demonstrates the feasibility and effectiveness of the proposed model. [ABSTRACT FROM AUTHOR]

The Acceleration Grid Power Supply (AGPS) is a system devoted to supply the acceleration grids of the MITICA experiment, the full scale prototype of the ITER Neutral Beam Injector (NBI), being built in Padova (Italy) to test the NBI in advance of the operation in ITER. The procurement of the AGPS is split in two parts: the low voltage conversion system, namely the AGPS-Conversion System (AGPS-CS,) being procured by the European domestic agency, and the high voltage DC Generators (AGPS-DCG), being procured by the Japanese domestic agency. After the contract award, in late 2015, the executive design phase of the AGPS-CS has been finalized. The paper will present the final design of the AGPS-CS and will discuss the main choices in particular concerning the protection from internal faults of the inverters. [ABSTRACT FROM AUTHOR]