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In the paper, a wideband tunable 4 × 4 Nolen matrix is proposed. By using the presented topology of the Nolen matrix, tunable output port phase differences can be realized by inserting one type of tunable phase shifters (T-PS). Besides, the in-band phase deviation error is minimized by adding compensation phase shifters (C-PSs) to the output ports of the Nolen matrix. Analytical design methods based on signal flow graphs and complex exponential signal are given to obtain the rigorous relationships of the coupling and phase shifts in the Nolen matrix. Besides, a detailed method for output ports phase slope compensation is provided. For validation, a prototype centered at 5.8 GHz is designed and fabricated. Measurement results agree well with the simulated ones. By using only one voltage to control the phase shifts of the T-PS in a 90° range for each input excitation of the Nolen matrix, a full 360° range of the progressive phase difference is realized by switching four input ports. The measured fractional bandwidth under 10 dB return loss and isolation is larger than 24.5% with the in − band ± 1.5 dB amplitude imbalance and ±15° phase deviation error for ports 1-4 excitations. Besides, for a more strict criterion of ±1 dB amplitude imbalance and 10° phase deviation error, the measured bandwidths are larger than 15% for all port excitations. [ABSTRACT FROM AUTHOR]

Floating-gate transistor lies at the heart of many aspects of semiconductor applications such as neural networks, analog mixed-signal, neuromorphic computing, and especially in nonvolatile memories. The purpose of this paper was to design a high-performance nanocrystal floating-gate transistor in terms of a large memory window, low power, and extraordinary erasing speeds. Besides, the transistor achieves a thin thickness of the tunnel gate oxide layer. In order to obtain the high-performance design, this work proposed a set of structure parameters for the device such as the tunnel oxide layer thickness, Interpoly Dielectric (IPD), dot dimension, and dot spacing. Besides, this work was successful in the virtual fabrication process and methodology to fabricate and characterize the 65 nm nanocrystal floating-gate transistor. Regarding the results, while the fabrication process solves the limitation of the tunnel oxide layer thickness with the small value of 6 nm, the performance of the transistor has been significantly improved, such as 2.8 V of the memory window with the supply voltage of ±6 V at the control gate. In addition, the operation speeds are compatible, especially the rapid erasing speeds of 2.03 μs, 28.6 ns, and 1.6 ns when the low control gate voltages are ±9 V, ±12 V, and ±15 V, respectively. [ABSTRACT FROM AUTHOR]

Megatrends, such as the proliferation of distributed generation, electrification, and the appearance of aggregator companies, put the low voltage power grids under intense pressure. Since the network infrastructure developments cannot keep up with the trends, distribution system operators turned to alternative solutions. Smart grid assets, such as on-load tap-changing distribution transformers or serial low voltage regulators, are promising solutions. However, the energy transition cannot be handled with the network expansive on the distribution level. Control centers are predicted to expand to this voltage level in the near future, and distribution system state estimation could be an enabler of all functionalities. On the low voltage level, data scarcity is a great challenge in observability; therefore, research must focus on the creation of pseudomeasurements and integration of available data sources. This paper examines the inclusion of smart assets from the conceptual point to the application on two sites, based on data from operational environments, both with a pseudomeasurement and an integrated metering point approach. The results showed that integrating smart assets could considerably mitigate voltage fluctuations, and reduce estimation errors by two magnitudes on the low voltage network. [ABSTRACT FROM AUTHOR]

The virtual impedance can suppress the low-frequency oscillation effectively caused by the power coupling effect for the grid-forming direct-drive permanent magnet synchronous generator (D-PMSG). However, there are few studies on the influence of virtual impedance on the subsynchronous oscillation caused by the interaction between the grid-forming D-PMSG and the weak grid. In this paper, the mechanism of virtual impedance improving the stability of virtual synchronous generator (VSG) control for the converter is revealed from the perspective of power coupling, and the influence of virtual impedance on the system stability in subsynchronous frequency range was analysed based on the sequence impedance model. The analysis results show that the virtual inductance cannot effectively improve the oscillation suppression effect, but the virtual resistance can greatly improve the damping characteristics of the system which has a good oscillation suppression effect. However, excessive increase in virtual resistance will cause power coupling oscillation, even subsynchronous oscillation, which shows limitations in subsynchronous oscillation suppression. To solve the problem, a dynamic voltage compensation control method based on active disturbance rejection control (ADRC) was proposed, and the parameters are designed by bandwidth method. The method can suppress the subsynchronous oscillation effectively in a certain frequency range under different grid strength and disturbance conditions. And it shows strong adaptability and good system robustness in weak grid. Finally, the effectiveness of the proposed oscillation suppression strategy was verified by time domain simulation. [ABSTRACT FROM AUTHOR]

This paper proposes a systematic method using the hybrid automata (HA) model for supervisory management design of power systems to increase stability. The HA model monitors the behavior of the power system and derives a model from which the system's stability is evaluated. In the modeling framework, the hybrid system formalism regulates continuous dynamics and discrete switching behavior. The proposed method extracts a system's control graph, state space, and transfer function, facilitating voltage stability evaluation. A discrete event system (DES) is employed to manage disturbances resulting from load surges, generator outages, capacitor banks, and under-load tap changer (ULTC) transformers. The ULTC transformer and the capacitor bank are utilized to examine the feasibility and effectiveness of the proposed supervisory controller design approach in the presence of distributed generation (DG). Simulation results showed the effectiveness of the HA-based supervisory controller in improving the control and voltage stability, as demonstrated by the generator rotor angle and bus voltage responses, power system eigenvalues, and the stability theorem of linear switching systems. The proposed method provides a promising solution for managing power system stability. [ABSTRACT FROM AUTHOR]

To improve the voltage and frequency stability and suppress the voltage harmonics of a microgrid, a virtual synchronous generator (VSG) control strategy based on the harmonic current bypass control is proposed in this paper. First, a robust voltage control link is added to the virtual excitation component of the traditional VSG control strategy to reduce the amplitude error of the inverter's driving voltage caused by the reactive power-voltage droop coefficient. A harmonic current bypass control link is then used to adjust the inverter's voltage signal to reduce the total harmonic distortion of the microgrid. Finally, a simulation model of the microgrid is established using the MATLAB/Simulink software, and its stability is analyzed. In addition, the proposed control strategy is also compared with the traditional droop control and traditional VSG control strategies, focusing on the frequency instability and harmonic suppression performance of the microgrid. The numerical simulation results verified the effectiveness and superiority of the improved VSG control strategy proposed in this paper. [ABSTRACT FROM AUTHOR]

Summary: This paper investigates the hybrid HVDC with cascaded multi‐infeed MMCs' basic control characteristic and designs the coordinates control strategy considering the DC voltage control and commutation failures of the LCC inverters. The complete basic UI curves of the hybrid HVDC are obtained, and the interaction mechanism of each converter is also clarified, which is in master‐slave control mode. Through the obtained basic characteristic, to reduce the commutation failures of the LCC inverter, the coordinated DC voltage control strategy with dynamic limiter is designed to enhance the AC voltage stability. And the coordinated DC voltage control method coped with the dynamic limiters is also designed. Based on the proposed method, the DC voltage can be stable and unbalanced active power can also be distributed reasonably by the DC voltage control strategy, while much more reactive power can simultaneously be released from VSC to support the stable operation of the LCC inverter. Such that the DC side operation and AC side voltage stability of the hybrid HVDC can both be improved. Finally, the simulations verify the theoretical analysis done in the paper. [ABSTRACT FROM AUTHOR]

Summary. The linear active disturbance rejection control (LADRC) is mainly applied for tracking a step signal, and it is inadequate to realize satisfactory performance in the control of a single-phase inverter whose reference signal is sinusoidal. In this paper, an improved voltage control strategy based on compound synchronous reference frame proportional-integral (SRFPI) control and LADRC is proposed. The SRFPI and LADRC remain relatively independent without complicating the control parameter design. Detailed theoretical analyses on the compound strategy and its performance are presented, indicating that it inherits the advantages of the two controllers. Moreover, contrast experiments are carried out to verify the feasibility and superiority of the proposed control strategy. The results show that the system achieves a small steady-state error, voltage tracking error, fast transient response, and low total harmonic distortion (THD) when feeding a highly nonlinear load. [ABSTRACT FROM AUTHOR]

Voltage stability margin is ensured through the reactive power resources. In order to generate the reactive power references and ensure the low-voltage ride-through (LVRT) control of a wind farm system based on squirrel cage induction generator, this paper proposed an optimal control approach based on fractional-order (FO) PI-fuzzy-PI (FOPI-fuzzy-FOPI) controller. The proposed control method ensures, also, the demand for active and reactive power predetermined by the transmission system operator (TSO) and satisfies the grid code recommendations. In order to achieve a faster tracking of state variables of the system, the FO operators are optimized using the particle swarm optimization algorithm (PSOA). Using FO operator and PSOA, the responses of the system can be improved. The proposed controller provides additional parameters for better tracking performance and faster convergence can be achieved. Numerical simulation results are presented to analyze the advantages of the proposed control approach to design a physically, realizable controller. The present results are compared with various control methods to show the superiority of the method proposed in this paper. [ABSTRACT FROM AUTHOR]

In recent times, neutral point piloted (NPP) or half-leg T-type multilevel inverter (MLI) becomes a promising topology for medium-voltage high-power applications. This T-type MLI is the best substitute for diode clamped multilevel inverter (DCMLI) due to its simple structure and absence of clamping diodes. However, the neutral point voltage control or dc bus capacitors' balance of NPP T-type MLI is a challenging task. Therefore, this paper presents a nonlinear sliding mode controller (SMC) for dc-link voltage balance and reference current control in distribution static compensator (DSTATCOM). For this, a three-level T-type MLI-based three-phase four-wire DSTATCOM is considered to eliminate current-related power quality issues such as harmonics, reactive power, load unbalance, and neutral current. The proposed NPP T-type-based DSTATCOM is compared with DCMLI and active DCMLI-based DSTATCOMs in terms of switching losses and cost. Simulation studies are carried out in MATLAB Simulink environment and further corroborated with experimental studies. Furthermore, the ability of the proposed SMC-based controller is compared with the PI controller under different operating conditions. [ABSTRACT FROM AUTHOR]

Background: Multilevel Inverters have become a viable alternative to two‐level inverters because of their superior power quality, however, the increase in number of switches with their corresponding voltage stress, and dc voltage sources are the major factors for higher number of levels. Aim: This paper proposes a modified and improved asymmetrical multilevel inverter with 15 output voltage levels. Materials and Methods: The distinguishing feature of the proposed topology is the reduced number of switches as compared to recently introduced topologies having the same number of levels. As the number of devices has a direct relation to the cost of the inverter, therefore, reducing the devices will decrease the cost and makes the system more reliable for use in potential applications. The three different extensions of the proposed circuit is also discussed in the paper. Nearest level control technique is used as a modulation strategy to control the output voltage of the proposed topology. Results and Discussion: The proposed Multilevel Inverter (MLI) has been simulated in MATLAB/SIMULINK environment. The THD analysis is also shown in the paper. Experimental results have been presented and discussed to validate the obtained simulation results. Power Loss analysis of the converter is also provided. It is done with the help of PLECS software. Conclusion: The presented topology have lesser value of total standing voltage (TSV) and at the same time, there is no requirement of an H‐bridge in the structure to achieve polarity reversal for the desired levels. [ABSTRACT FROM AUTHOR]

This paper endeavours a control scheme for optimal control of voltage and frequency of power inverter which relied upon distributed generation in cognitive microgrid using soft computational methods. It gives sound direction on how to control the active power flow, voltage‐frequency regulation, and sharing of power among various components of MG. The classical voltage–frequency control strategy in parallel with the modern control method is well excavated in the present paper. Moreover, modulation techniques, variants of reference frames, power quality indices are covered blatantly. Thus, the paper gives fast insight and understanding to the engineers working in this niche area. [ABSTRACT FROM AUTHOR]

Summary: This paper proposes a new control strategy for enforcing a AC‐DC hybrid microgrid to attain stable responses in both steady state and dynamic operating conditions. The proposed controller is designed based on combining direct Lyapunov method and small signal linearization (SSL). The dynamic parts of converter control functions are achieved through providing the global asymptotical stability of the hybrid microgrid by using its total saved energy function. Then, the steady‐state components of the controller, unlike other existing Lyapunov‐based methods, are obtained according to SSL‐based mathematical terms as the main novelty of this paper. This novelty simultaneously provides several contributions within the proposed control technique structure as (a) the direct control of the PCC voltage frequency and DC‐link voltage errors, (b) the enhanced decoupling feature for DC/AC converter current, and (c) the direct control of the input voltage error for bidirectional DC/DC converter. Finally, comparative simulation results in MATLAB/Simulink software are presented to verify the superiority of proposed controller combined with SSL under AC and DC load variations, discharging/charging of storage unit, different grid power factors and AC loads shared among grid side and DC sources. [ABSTRACT FROM AUTHOR]

This paper proposes a novel predictive strategy based on a model predictive control (MPC) for the interior permanent magnet synchronous motors (IPMSMs) driven by a three-level simplified neutral-point clamped inverter (3L-SNPC) for electric vehicle applications (EVAs). Based on the prediction of the future behavior of the controlled variables, a predefined multiobjective cost function incorporates the control objectives which are evaluated for every sampling period to generate the optimal switching state applied directly to the inverter without the modulation stage. The control objectives in this paper are tracking current capacity, neutral-point voltage balancing, common-mode voltage control, and switching frequency reduction. The principal concepts of the novel scheme are summarized as follows: first, the delay compensation based on the long horizon of prediction is adopted by a multilevel power converter structure. Second, based on the modified Lyapunov candidate function, both stability and recursive feasibility are ensured of the proposed predictive scheme. Third, the practicability of the real-time implementation is improved by the proposed "static voltage vector" (SVV) and "single state variation" (SSV) principles. Finally, the proposed concepts are implemented in the novel predictive control formulation as additional constraints without compromising the complexity and the good performances of the predictive controller. Therefore, only the switching states that guarantee the stability and the reduction of calculation burden criteria are considered in the evaluation of cost function. The proposed predictive scheme based on the "SVV" principle has demonstrated superior performance in simulation compared with the proposed scheme with the "SSV" principle. The computational burden and switching frequency rates are reduced by 35% and 56.22%, respectively. [ABSTRACT FROM AUTHOR]

In this paper, an alternative strategy for real-time control of active distribution network voltage is developed, not by controlling the bus voltage as in the various centralized, decentralized, and local approaches presented in literature but rather by only eliminating the impact produced by active and reactive power of distributed generation (DG) units on the voltage of all network nodes and keeping the traditional voltage control systems dealing with the same constraints of passive systems. In literature, voltage deterioration introduced by DGs has been reported as one of the main obstacles for the interconnection of large amounts of DG units to the existing networks. In this paper, the novel control strategy is based on a sensitivity formula developed to calculate the compensation needed for additional distributed flexible AC transmission system (D-FACTS) devices to push and pull the exact reactive power and to eliminate the impact produced by DGs on the network voltage profile. The criteria of the allocation of the var devices and the required network reinforcement are developed in this paper, considering all possible topology structures, and an innovative codification method is introduced to reduce the needed computation time and communication data to actualize the sensitivity coefficients and get the proposed control approach flexible with network topology reconfiguration. The risk of the conflict of the proposed control system with the traditional voltage equipment is reduced due to the fast capability of D-FACTS devices to regulate their reactive power in finer granularity. A case study of two meshed IEEE 15-bus feeders is introduced to compare the voltage behavior with and without the presence of DG units and to evaluate the total system losses. The proposed method could be used for the interconnection of the first generation units in emerging networks, which does not yet have an active voltage control strategy, as it could be used for DG units not able to be connected to existing centralized control systems and it could also be used as the principal voltage control strategy, with the extension for several neighboring units and the preservation of the traditional voltage control systems. [ABSTRACT FROM AUTHOR]

To eliminate the weighting factor tuning effort of typical finite-set model predictive control (FS-MPC), this paper proposes a weighting factor-less sequential model predictive control (SMPC) scheme for LC-filtered voltage source inverters. Two independent cost functions for minimizing capacitor-voltage and inductor-current tracking errors are deployed in a cascaded structure, eliminating the weighting factor. First, the optimal cascade order of the cost function is selected by the internal relationship of two control variables. Then, a graphical method is proposed to determine the optimal number of candidate voltage vectors selected from the first cost function. Moreover, to realize the strict current limitation, the current-constraint term is proved to be included in the voltage-related cost function. Another attractive feature of the proposed SMPC is that a smoother inductor-current starting response can be obtained compared to typical FS-MPC. Simulation and experimental results verify the feasibility of the presented approach. [ABSTRACT FROM AUTHOR]

Load-sharing and voltage regulation are key challenges in low voltage dc microgrid systems. Droop-based decentralized control methods are used to control dc grids which cannot achieve these challenges simultaneously due to unequal voltages and load power variations. Centralized control schemes can achieve these challenges using high bandwidth communication. However, the failure of a single central controller can degrade performance and reliability. In addition, cascaded proportional-integral (PI) type controllers are used to control the voltage and current loop of each power electronic converter. These controllers suffer stability and show slower dynamic responses. Furthermore, control parameters cannot be optimized for different operating conditions. To address these challenges, a distributive control method using an equivalent sliding mode (SM) controller utilizing low bandwidth communication is proposed in this paper. The distributive method improves reliability and achieves load sharing and voltage regulation simultaneously. Furthermore, in SM, both voltage and current loop operate in the parallel configuration which improves the dynamic response and shows stability in all operating conditions. To analyze, a system model is developed, and existence and stability conditions are verified. Detailed simulations are carried out to show the steady-state and transient performance. The presented results show the effectiveness of the proposed scheme. [ABSTRACT FROM AUTHOR]

With the integration of high proportional photovoltaics (PVs) into distribution networks, the superposition of uncertain output power of PVs and stochastic load demand fluctuations have posed a serious challenge to voltage stability. In this paper, a multitimescale decomposition-coordination-based voltage control method is proposed under the cloud-edge cooperative architecture. The distribution network is firstly decomposed into several subnetworks. In each subnetwork, the edge computing device is equipped to realize the distributed control and provide external computing resources for the cloud center. Then, a multitimescale control scheme containing the interval dispatch stage and the real-time time-window stage is proposed. In the interval dispatch stage, a cloud-edge collaborative calculation strategy considering balanced resource allocation is well designed to obtain the global optimal power flows and the corresponding reference operating points of the voltage control equipment. Meanwhile, in the real-time time-window stage, a consensus-based voltage correction mechanism under the optimal power flow boundary constraints is designed to avoid the voltage violations caused by unexcepted power fluctuations deviating from the representative scenarios. Simulation results with the improved 33-bus and IEEE 123-bus systems have demonstrated the effectiveness of our proposed method. [ABSTRACT FROM AUTHOR]

With the integration of high proportional photovoltaics (PVs) into distribution networks, the superposition of uncertain output power of PVs and stochastic load demand fluctuations have posed a serious challenge to voltage stability. In this paper, a multitimescale decomposition-coordination-based voltage control method is proposed under the cloud-edge cooperative architecture. The distribution network is firstly decomposed into several subnetworks. In each subnetwork, the edge computing device is equipped to realize the distributed control and provide external computing resources for the cloud center. Then, a multitimescale control scheme containing the interval dispatch stage and the real-time time-window stage is proposed. In the interval dispatch stage, a cloud-edge collaborative calculation strategy considering balanced resource allocation is well designed to obtain the global optimal power flows and the corresponding reference operating points of the voltage control equipment. Meanwhile, in the real-time time-window stage, a consensus-based voltage correction mechanism under the optimal power flow boundary constraints is designed to avoid the voltage violations caused by unexcepted power fluctuations deviating from the representative scenarios. Simulation results with the improved 33-bus and IEEE 123-bus systems have demonstrated the effectiveness of our proposed method. [ABSTRACT FROM AUTHOR]

This paper presents the dual‐mode control to improve the power quality (PQ) of three‐phase four‐wire grid interfaced photovoltaic (PV) battery system in a single‐stage configuration, where the current control is used at normal circumstances for the grid‐interactive mode and for the grid interruption, the system operation is through the voltage control. The transient free switching between grid interactive and off‐grid modes is executed by a power electronics switch, thus at disconnection, the system gives reliable and incessant power to the loads. The weight of the active current constituent from the load current is acquired using Mathew's algorithm‐based adaptive filter. The voltage control regulates the frequency and voltage across the loads in off‐grid mode. The current control used for a voltage source converter mends the PQ namely current harmonics extenuations and unity power factor operation and it utilizes the solar PV's array power feed‐forward unit for the enhancement of the system's dynamic performance. The incremental conductance technique is applied for obtaining the maximum PV array's power. The addition of a battery across the DC link is realised using a DC–DC buck‐boost converter. The battery is discharged and charged in accord with the load's variation. This converter's control sustains the maximum power point tracking voltage. The system's performances for the steady‐state and dynamic situations, such as solar insolation change, load perturbation, load unbalancing and neutral current compensation, are authenticated on a developed prototype through test results. [ABSTRACT FROM AUTHOR]

This paper proposes the application of a current mode control on a static compensator (STATCOM). The proposed method uses constant switching frequency. Hence, dominant switching harmonics are filtered easily. This approach is also simple and does not need complex calculations. As a result, it will be an ideal candidate for the implementation of controllers or FPGAs. It should be noted that a single‐phase five level reversing voltage (RV) inverter is selected for the STATCOM. The topology has superiorities over conventional multilevel topologies in terms of the control circuit, switching frequency, and the number of components. The simulation results by MATLAB/Simulink prove successful mitigation of voltage sag by the proposed approach. A prototype based on the proposed method is also developed and examined successfully to evaluate voltage sag mitigation. The harmonic spectrum of the STATCOM is also presented to illustrate the equipment compatibility with IEEE 519 harmonic standard. [ABSTRACT FROM AUTHOR]

Summary: This paper introduces an optimal voltage control (OVC) framework for islanded microgrids (MGs) as a unified hierarchical control scheme, started from bus voltage set‐points optimization at tertiary level, then effectively followed by secondary control, which controls the distributed energy resources via their primary level controllers. The distributed control structure is proposed here for both tertiary and secondary levels to benefit from higher reliability, avoidance of a single point of failure, and a relatively simple communication system. At the tertiary level, a new distributed voltage protocol, based on the Lyapunov theory, is proposed to optimize power losses and voltage profile deviations in the MG. The obtained optimal voltage references are passed to the secondary level, in which a modified distributed protocol (MDP) is utilized to ensure the OVC and dynamic stability. In addition, the proposed MDP can maintain the critical bus voltage against load changes until the next optimal set‐point updates. The performance of the MDP is examined for different scenarios such as load changes and DGs plug and play operation in the MATLAB/Simulink environment. [ABSTRACT FROM AUTHOR]

Summary: The intermittent nature of renewable energy generation and the variable AC and DC loads are major factors that offer great challenges in power management for AC/DC hybrid microgrids. In this context, this paper presents a coordinated AC frequency vs DC voltage control (CFVC) scheme for managing contemporary renewable energy‐based hybrid AC/DC microgrids. The proposed control strategy enables appropriate power interactions between the AC and DC subgrids while sharing power fluctuations in a coordinated way. Both the AC and DC subgrids support each other in accordance with their normalized relative changes in AC frequency and DC voltage, respectively. The proposed CFVC scheme is designed using fractional‐order‐proportional‐integral‐derivative (FOPID) controllers, and bacterial‐foraging optimization (BFO) method is employed for calculating the design parameters, viz. the controller gains and set‐point orders. A typical photovoltaic (PV) wind‐battery‐based hybrid AC/DC microgrid is modelled and investigated, and the usefulness of the proposed scheme is validated under the renewable energy variations and load perturbations. [ABSTRACT FROM AUTHOR]

Summary: The conversion of the tidal power captured by the marine current turbine to electrical power depends highly on the applied control strategy. However, in the presence of nonlinearities, parametric uncertainties, and external disturbance, the controller design process is challenging task. This paper proposes an energy‐based control approach for a grid‐connected permanent magnet synchronous generator (PMSG)‐based marine current energy conversion system. This method combines a new passivity‐based voltage control (PBVC) with a nonlinear observer. The PBVC designs the desired dynamic of the system, while the nonlinear observer is used to reconstruct the measured signals. The main contributions and motivation of this work include the extraction of maximum power from the tidal current, integrating it to the grid, and forcing the closed‐loop system's energy to passive state. The mentioned objectives are achieved by reshaping system's energy and introducing a damping control term that compensates the nonlinear phenomena in a damped way rather by the cancellation and it also establishes a duality concept between the observer and the PBVC. Two steps are required to design the proposed controller: In the first step, the reference current is formulated based on the reference torque using a proportional‐integral‐derivative controller. As a second step, the overall control law is computed by the passivity‐based combined nonlinear observer and voltage controllers. To validate the performance of the system under the proposed control, a comparison with the second‐order sliding mode control and the conventional proportional‐integral control methods is presented. The proposed method is tested in MATLAB/Simulink environment under different operating conditions and from the presented results it is evident that the proposed controller showed robustness against parameter changes and ensured fast convergence of the states. [ABSTRACT FROM AUTHOR]

In the off-grid microgrid cluster, the energy storage device is mainly charged and discharged to maintain the stability of the bus voltage and the system power balance. Generally, the voltage and current double closed-loop control and fuzzy control are adopted for the energy storage converter. The traditional double closed-loop control parameters and the scale factor and quantization factor in fuzzy control cannot be adjusted in real time during system operation, resulting in slower dynamic response and weak anti-interference ability of the system. In response to the above problems, this paper proposes an adaptive genetic fuzzy double closed-loop control, which can adjust the PI control parameters in real time by adjusting the quantization factor and the scale factor to optimize the control effect. The simulation platform is built in MATLAB/Simulink and the simulation results show that the adaptive genetic fuzzy double closed-loop control combines the advantages of fuzzy and PI control. Under different working conditions, the system has not only a fast dynamic response, small overshoot, and strong anti-interference ability but also good robustness. [ABSTRACT FROM AUTHOR]

This paper shows a new manner to exploit the STM32F407 board in order to perform the processor in the loop (PIL) testing by reducing significantly the co‐simulation time. This method requires an FT232RL USB‐UART converter board as an external serial communication interface. The main advantage of this external device lies in the setting of its baud‐rate using the aliasing technique. This technique provides an efficient solution to transfer data between embedded board and computer at high baud‐rate. It allows speeding up the PIL testing and, therefore, makes it more flexible. The studied grid connected wind‐turbine system is based on permanent magnetic synchronous generator (PMSG) followed by back‐to‐back bidirectional converters. The grid side converter (GSC) ensures the DC bus voltage control as well as the unity power factor, while the machine side converter (MSC) ensures the PMSG speed control. The method of the decoupled current control is presented for the GSC. The optimum tip speed ratio (OTSR) algorithm–based maximum power point tracking (MPPT) technique is developed for MSC. Both power and control parts are initially designed and simulated in the same MATLAB/Simulink environment. Once the Simulink model behaves properly and meets the desired requirements, the proposed PIL test is then carried out. The C code is automatically generated from controllers and implemented on the STM32F407 board that acts as an external controller, meanwhile power part still works on the host computer. The PIL test results show the efficiency of the chosen control algorithms and dynamic behavior of the full wind‐turbine system. They also show that the controllers simulated under MATLAB/Simulink behave in the same way once executed on the embedded board. [ABSTRACT FROM AUTHOR]

Summary Multi‐phase converters for more than three‐phase applications have become increasingly important topics due to their distinct advantages compared with the conventional three‐phase converters. This paper proposes a modified PWM switching technique for direct AC‐AC three‐to‐five phase matrix converter to realize output voltage waveform with low total harmonic distortion (THD) and reduce the total commutation number of its bidirectional power switches in each control period, simultaneously. In order to minimize the switching loss and reduce the voltage stress on all power switches of the matrix converter, the proposed PWM switching pattern prevents any state of direct commutation and switching between the maximum and minimum grid phase voltages. This in‐turn enhances the converter durability and lifetime in addition to the power density. Also, the proposed PWM switching technique has the ability to fully control the load voltage waveform and its frequency to meet the reference values. In addition, it has the ability to control the three‐phase grid currents to be sinusoidal waveforms and in‐phase with grid voltages for unity power factor. Moreover, it enables voltage transfer ratio of 78.86% of the source input voltage. A laboratory prototype has been carried out in order to investigate the effectiveness of the proposed switching technique. [ABSTRACT FROM AUTHOR]

With the increasing penetration rate of distributed renewable energy in power systems, the control strategy of virtual synchronous generator (VSG) is widely used for several years. Some existing VSG control strategies have been able to solve the stability problems caused by the abnormal grid voltage, but the effects of the inertia coefficient and the droop coefficient on the voltage stability are not taken into account. In order to further improve the voltage stability of the microgrid system, a voltage control strategy of VSG based on self-adaptive inertia coefficient and droop coefficient is proposed in this paper. When the voltage is far from the steady state, the increase of the inertia coefficient can decrease the voltage deviation. On the contrary, when it is close to the steady state, the decrease of the inertia coefficient can make the system response speed accelerate. According to the real-time voltage deviation, the droop coefficient can change adaptively to decrease the adjusting time and the voltage deviation during the disturbance. Finally, the simulation model of VSG is built by MATLAB/Simulink for conducting simulation experiments. Compared with other strategies, the correctness and effectiveness of the proposed control strategy are validated. [ABSTRACT FROM AUTHOR]

Summary: This paper presents the combined voltage and frequency control of three‐area multi‐source interconnected power systems, having thermal‐solar thermal power plant, thermal‐wind and hydrothermal‐geothermal power plants. A maiden attempt has been made to incorporate one of the energy storage devices called redox flow battery (RFB) in all areas. Appropriate system non‐linearity constraints are considered for both thermal and hydro plants. A new cascade controller called cascade fractional‐order PD with filter and fractional‐order proportional‐integral‐derivative (PID) with filter (CFOPDN‐FOPIDN) is proposed as a secondary controller in the unified automatic load frequency control (ALFC) and automatic voltage regulator (AVR) system. A novel optimization algorithm called artificial flora algorithm is used to optimize the controller parameters. From the observation of the system dynamic responses, it reveals that the CFOPDN‐FOPIDN controller is superior to the FOPID, PIDN and PI controllers. The unified ALFC‐AVR study exhibits that the AVR loop enhances the system dynamics considerably. It is observed that the system oscillations are substantially reduced along with the peak deviation and settling time in the presence of RFB. Moreover, the combined frequency deviation and area control error as an input signal to the RFB outperforms the individual one. The system performance improves with an increase in the RFB gain value. Furthermore, it is divulged that a larger frequency deviation leads to a faster rate of change of frequency. Eventually, the sensitivity analysis reveals the sturdiness of the proposed controller. [ABSTRACT FROM AUTHOR]

In this paper, three model predictive current control (MPCC) schemes for permanent magnet synchronous motors (PMSM) are studied. The first control scheme is the traditional optimal duty cycle model predictive current control (ODC-MPCC). In this scheme, according to the principle of minimizing the cost function, the optimal voltage vector is selected from the six basic voltage vectors which are optimized simultaneously with the duty, and then, the optimal voltage vector and its duty are applied to the inverter. In order to reduce the computational burden of ODC-MPCC, a second control scheme is proposed. This scheme optimizes the voltage vector control set, reducing the number of candidate voltage vectors from 6 to 2. Finally, according to the principle of minimizing the cost function, the optimal voltage vector is found from the two voltage vectors, and the optimal voltage vector and its duty cycle are applied to the inverter. In addition, in order to further improve the steady-state performance, another vector selection method is introduced. In the combination of voltage vectors, the third control scheme extends the combination of voltage vectors in the second control scheme. The simulation results show that the second control scheme not only reduces the computational burden of the first control scheme but also obtains steady-state performance and dynamic performance equivalent to the first control scheme. The third control scheme obtains better steady-state performance without significantly increasing the computational burden and has dynamic performance comparable to the first and second control schemes. [ABSTRACT FROM AUTHOR]

Summary: Tariffs for ancillary services like reactive power are a significant tool for raising energy efficiency in the distribution systems. In this paper, a new method for the valuation of reactive power support provided by photovoltaic (PV) systems is proposed. As a valuation approach, it is assumed that the voltage regulation service can be individually provided by other sources like shunt reactors or demand response programs whose service prices have been formerly regulated. The proposed voltage control method is modeled by a network partitioning approach and the distributed algorithm called the alternating direction method of multipliers (ADMMs). Moreover, the uncertain nature of PV generation and load demand is modeled by a stochastic method. The proposed method is tested on a real rural distribution system and 123 bus IEEE distribution test system. The result evidence that the proposed method has a lower computation time compared to the centralized method in addition to having the same accuracy. For distribution companies, also, the proposed method of reactive power valuation will be a basis for pricing reactive power service provided by PVs. [ABSTRACT FROM AUTHOR]

This paper introduces a study of reduced devices count symmetric multilevel inverter (MLI) under two PWM techniques for AC applications. The MLI uses two DC sources to synthesize five‐level output voltage at a reduced switching devices number. The MLI employs five switching devices comprising the main and auxiliary circuits. The main circuit is a single‐phase H‐bridge inverter, which controls the output voltage polarity. The auxiliary circuit controls the input DC bus voltage by altering the number of the input DC cells to the frontend of the main circuit. Two PWM techniques are considered to control the MLI output based on minimum power loss and reduced total harmonic distortion, which in turn, elect the inverter application. To verify the effectiveness of the proposed MLI as well as the importance of the two PWM techniques, the five‐level inverter has been carried out experimentally using a laboratory prototype. DSPACE‐DS 1103 digital controller is utilized, to implement the experimental system controller, for controlled load voltage regulation. [ABSTRACT FROM AUTHOR]

Stabilization of DC‐link voltage is indispensable for the satisfactory operation of three‐phase electronically coupled photovoltaic (PV) system. Practically, a challenge is to promptly and effectively settle the DC‐link voltage with minimum peak magnitude and settling time to its pre‐disturbance level when exposed to disturbances in the load and solar insolation level. The classical methods of DC‐link voltage stabilization employ a proportional‐plus‐integral (PI) compensator, and its gain coefficients are modulated through a cumbersome trial‐and‐error approach. Nevertheless, this approach does not yield superior results, especially under the wide interruptions in operating conditions due to nonlinear and time‐varying characteristic of the PV module. These concerns have resulted in the emergence of multiple meta‐heuristic techniques to optimally tune PI compensator gain coefficients. Nevertheless, most of these methods call for the ingrained paradox between computational efficiency and dynamic performance. Driven by this drawback, a proposal based on grey wolf optimizer (GWO‐PI) is described in this paper to serve the following control targets: (a) be able to improve harmonic filtering with computational effectiveness, and (b) to ensure superior performance under exposure to interferences in the load and solar insolation level. Good agreement in MATLAB/Simulink simulation studies and experimental evaluations establish that the proposed GWO‐PI outperforms the existing standardized optimization techniques such as particle swarm optimization (PSO‐PI) and gravitational search algorithm (GSA‐PI) in aspects of peak magnitude and settling time. Besides, it practically enables an improved harmonic filtering feature and complies with stringent harmonic distortion limit recommended in the IEEE revised standard 519‐2014. [ABSTRACT FROM AUTHOR]

Traditional power networks with generation in upstream and consumption in the downstream were controlled with centralized controls like SCADA. However, in order to facilitate the penetration of distributed generation, the concept of microgrid was popularized. A microgrid can operate both in grid-connected and in islanded modes. One of the challenges in the microgrid environment is to provide both voltage control and maintain the system frequency while ensuring the stability of the network. This paper is a literature survey focused on different microgrid control techniques with different levels of communication especially in islanded operation. [ABSTRACT FROM AUTHOR]

Summary: Conventionally, voltage profile are regulated by controllers that are not operational flexible to the system dynamism and challenges offered by the integration of renewable energy sources. Consequently, there is a need for the adaptive coordinating mechanism as an interface between the passive network and the new active network. This will provide a platform for the smooth integration of distributed energy resources in most developing countries where traditional network is still operational. This paper proposes an algorithm for real‐time multiperiod adaptive compensation of network reactive power support based on hierarchical structure and decentralized layered multiagent system voltage coordinating scheme. A multiperiod voltage control algorithm replicates the daily load flow evaluation aiming at ameliorating voltage fluctuation over a 24‐hour simulation period. The algorithm applies the decentralized voltage control mechanism to monitor the network parameters and dynamically evaluate the capacity of the capacitor banks (CBs) to be injected for voltage compensation. This mitigates the challenges associated with under and over reactive power compensation experienced in the day‐ahead programming and manual switching operation. The algorithm works in conjunction with an on‐load tap changing transformer (OLTC) and energy storage system (ESS). The ESS complements the OLTC during switching delay, dip in its output root mean square and voltage fluctuation as network loading condition varies. The effectiveness of the proposed method is verified on standard IEEE 33 and 118‐bus distribution systems. The results show an improved voltage performance and reduction in stress/complexity associated with load and renewable generation forecast in manual switching operations. [ABSTRACT FROM AUTHOR]

As a novel topology of microgrid, the output voltage control of MMC half bridge series microgrid (MMC-MG) is rarely studied. In this paper, on the basis of fully analyzing the mechanism of output voltage fluctuation of MMC-MG under the condition of islanded mode, a control strategy of a hybrid energy storage system is proposed to reduce the generating module (GM) DC-link voltage fluctuation caused by the randomness of renewable energy microsource output power. Moreover, in order to further improve the stabilization of the MMC-MG output voltage and meet the requirements of fast voltage recovery and antijamming, a sliding mode controller is designed. Then, a voltage fluctuation compensation controller is designed to suppress the DC component and fundamental frequency deviation of system output voltage caused by GM DC-link voltage fluctuation. The proposed control approach is validated against simulations using MMC-MG models with 4-GM per arm. The results show that the proposed hybrid energy storage control strategy can suppress the GM DC-link voltage fluctuation, the sliding mode controller can stabilize the system output voltage when the load drastic changes, and the fluctuation compensation strategy can suppress the DC component and the fundamental frequency deviation of system output voltage. [ABSTRACT FROM AUTHOR]

The photovoltaic DC microgrid has strong nonlinearity and time variation. Therefore, traditional dual closed-loop control strategy of voltage and current based on PI controller cannot effectively restrain the fluctuation and impact of DC bus voltage when the dynamic response of the system is improved. Under this situation, in this paper, the fuzzy-PI dual-mode controller is designed to upgrade the traditional dual closed-loop control, taking voltage outer ring into consideration, which is adopted to achieve good transient performance while the bus voltage deviation is large. While the bus voltage deviation is small, the PI controller is utilized for good steady-state performance. Hence, simulation and experimental results show that the fuzzy-PI dual-mode controller has the same advantages with both fuzzy control and PI control; in other words, it has the features of speedy response, low overshoot, good robustness, and strong anti-interference under different working conditions. [ABSTRACT FROM AUTHOR]

Summary: This paper presents cascaded topology of three‐phase neutral‐point‐clamped converters (NPCC)s. Two or more NPCCs are cascaded in their AC sides through transformers. This multilevel inverter (MLI) is a transformer‐based single‐source inverter with trinary asymmetry. Compared with conventional and advanced diode‐clamped multilevel inverters, the proposed MLI achieves more levels on output voltage. From cost, number of components, volume, complexity and efficiency aspects, the proposed inverter is an optimized and advanced inverter. An individual space vector modulation (SVM) method has been developed for voltage control of the inverter. The neutral‐point voltage of the inverter is balanced conveniently by the SVM method. The proposed inverter is suitable for constant‐frequency applications. Simulation and experimental results of a 17‐kVA prototype verify the efficiency of the proposed arrangement. [ABSTRACT FROM AUTHOR]

This paper introduces a direct model predictive voltage control (DMP VC) for a sensorless five-phase induction motor drive. The operation of the proposed sensorless DMP VC is based on the direct control of the applied stator voltages instead of controlling the torque and flux as in model predictive direct torque control (MP DTC). Thus, the simplicity of the control system is enhanced, which saves the computational time and reduces the commutation losses as well. The methodology based on which the proposed sensorless DMP VC performs its operation depends on minimizing a cost function that calculates the error between the reference and actual values of the direct and quadrature (d-q) axes components of stator voltages. The reference values of d-q components of stator voltages are obtained through incorporating the deadbeat control within the proposed model predictive system. A robust back-stepping observer is proposed for estimating the speed, stator currents, rotor flux, and rotor resistance. The validity of the proposed sensorless DMP VC is confirmed through performing detailed and extensive comparisons between the proposed DMP VC and MP DTC approach. The obtained results state that the drive is exhibiting better performance under the proposed DMP VC with less ripples content and reduced computational burden. Moreover, the proposed back-stepping observer has confirmed its effectiveness in estimating the speed and other variables for a wide range of speed operation. [ABSTRACT FROM AUTHOR]

This paper presents a sensorless control scheme for the stand-alone brushless doubly fed induction generator (BDFIG) feeding nonlinear loads. The fundamental and harmonic components of the distorted power winding (PW) voltage caused by the nonlinear loads are extracted and controlled separately. A rotor speed observer is employed to estimate the speed based on the PW voltage and control winding (CW) current without the need of any other machine parameters except for the number of pole pairs. Since the d- and q-axis references of the CW current from the PW voltage control loop contain both dc and ac components, which cannot be tracked easily by conventional PI controllers, a CW predictive current controller is designed to regulate the CW current. Finally, the performance of the proposed control scheme is verified by comprehensive experiments on a 35-kVA prototype BDFIG. [ABSTRACT FROM AUTHOR]

This paper presents a microgrid composed of photovoltaic (PV) array‐battery energy storage (BES) and a diesel generator (DG) set. A bidirectional DC–DC converter (BDDC) is used to integrate the BES to the DC link of the voltage source converter. The BDDC controls the voltage at the DC link to the output voltage of the maximum power point tracking (MPPT) controller, thereby PV array always operates at its maximum power point (MPP). Another function of the BDDC is to block the second‐order harmonic from the BES, when the microgrid is feeding with unequal loads in the three phases. The magnitude of DG set terminal voltages is regulated by an electronic automatic voltage regulator (AVR) that controls the excitation to the synchronous generator. A fast, accurate and oscillations‐less modified variable step size least mean square based adaptive control is used here for improving the power quality. The main features of this microgrid topology are the operation of the PV array at its MPP in all operating scenarios, regulation of DG set voltages, harmonics elimination, balancing of DG set currents and reactive power compensation for the unity power factor operation. [ABSTRACT FROM AUTHOR]

Due to several problems such as global concern about environmental pollution, renewable energy has become an alternative source of energy. In situations such as small local loads far from the main grid, standalone hybrid power system (HPS) with inevitable unbalanced loading condition is preferred for the global grid. The four-leg inverter with a simple as well as well-performance control method is a good solution to support this condition. In this paper, with respect to the average and discretized model of the inverter, a new digital controller is proposed in the abc reference frame to control the load voltages. The proposed controller offers several advantages such as simplicity, fast dynamic response, no need for transformation among different reference frames, and full compatibility with digital implementation which makes it as an excellent option to be employed in such systems. In addition, a new hybrid controller is also proposed which not only has the advantages of the proposed digital controller but also shows superior performance under nonlinear loads without imposing a high computational burden. To verify the effectiveness of the two proposed controllers, several simulation and experimental tests under different scenarios on a 3 kW setup are performed. [ABSTRACT FROM AUTHOR]

Summary: Energy conservation through voltage reduction and distributed energy storage (DES) technology emerged as a potential candidate for peak load relief in distribution grid. However, lack of coordination between network controls such as conservation voltage reduction (CVR) and assets (DES) may cause detrimental impact on smart grid operations. Therefore, this paper reports on the need for coordination of CVR and DES for maximizing the benefits of both approaches. The impact of integrated operation of CVR devices and DES on energy saving and peak demand reduction have been investigated. The CVR scheme has been implemented using discrete gravitational search algorithm‐driven Volt‐ampere reactive (VAR) optimization (VVO) in the presence of distributed energy sources (DER). Such a smart grid‐enabled centralized CVR scheme has been proposed to be deployed in the grid and integrated with a community energy storage (CES) as DES. The main task of the VVO engine is to minimize the total power demand through optimal settings of Volt‐VAR control (VVC) devices. In order to demonstrate the benefits of integrated operation of CVR and CES, the studies have been carried out in three cases, namely without CVR, VVO‐based CVR, and CVR with CES in presence of both nonrenewable and renewable (wind) type DERs. Moreover, the impact of the proposed method has not only been demonstrated on hourly varying load of the year but during peak load hour also. Besides, the techno‐economic and environmental assessment of combined operation of CES and CVR has been done. The Institute of Electrical and Electronics Engineers (IEEE) 123‐bus unbalanced distribution network with the modification to include the DER and CES system apart from CVR devices has been chosen to corroborate the performance of the proposed method. The test results reveal that the proposed integration method of CVR and CES achieve higher peak sharing and energy saving with reduced carbon emission. In addition, the method assists the demand balancing. Besides, the by‐product of CES control strategy has been demonstrated for mitigation of rise in neutral currents. [ABSTRACT FROM AUTHOR]

Summary: Increased energy demands due to rapid industrialization, environmental concerns with fossil fuel–based generation, diminishing fossil energy resources, transmission network congestion, and technical performance deterioration are the motivations behind the integration of small renewable distributed generation (DG) units and turning the existing power systems into a restructured one. Optimizing the technical benefits offered by DG placement is a well‐known challenge for distribution network operators (DNOs) for both fossil and renewable energy resource–based DGs, but renewable DG systems have several power quality (PQ) challenges associated additionally. Power quality is a very significant characteristic of renewable DG systems because today's loads are more sensitive to PQ disturbances and penetration of renewable energy as well as nonlinear loads is proliferating in distribution power networks. So the need for innovative power quality improvement (PQI) techniques becomes inevitable due to ongoing reformation in traditional distribution networks by the integration of renewable energy. This article presents a comprehensive analysis of power quality challenges with grid integration of renewable DG systems and current research status of associated mitigation techniques. Firstly, this paper puts emphasis on theoretically illustrating all the crucial power quality challenges associated with grid integration of renewable energy, and secondly, a thorough survey, of all PQI techniques introduced till date, is elaborated along with highlighting the opportunities for future research. Furthermore, all the crucial power quality issues, the impact of high penetration of renewable energy and mitigation techniques on power quality, are demonstrated also by simulating a grid integrated PV‐based DG system in MATLAB/Simulink. This article is believed to be very beneficial for academics as well as industry professionals to understand existing PQ challenges, PQI techniques, and future research directions for renewable energy technologies. [ABSTRACT FROM AUTHOR]

The main purpose of this paper is to investigate the mechanism of sliding phenomenon in Filippov (nonsmooth) dynamical systems by attractor analysis and vector analysis. A corresponding simple model based on Chua's circuit with periodic excitation was introduced as an example. The attractor analysis proposed in our previous work is used to discuss the complicated oscillations of the Filippov system. However, it failed to perfectly explain the sliding phenomena and establish an analytical method of constant voltage control. Therefore, the geometric structure and analytic conditions of sliding bifurcations in the general n-dimensional piecewise smooth system are discussed in detail by vector structure analysis. The prospects of practical application of this method are also discussed in the end. [ABSTRACT FROM AUTHOR]

This paper proposed a fractional-order PID controller and active disturbance rejection control (ADRC) method for the current compensation of active power filter (APF). The control method consists of two closed loops. One is a reference current tracking loop based on the ADRC controller, which can treat the internal and external uncertainties of the system as a whole. The other is the voltage control loop with the fractional-order PID controller for more flexibility. Simulation results demonstrate that the proposed control method has a stronger robustness and higher compensating precision comparing with the double-loop PID control method. [ABSTRACT FROM AUTHOR]

The solar power generation includes certain randomness and volatility, coupled with dynamic load involved in power fluctuations, which renders microgrid having certain unplanned instantaneous power during the process of real-time operation, so as to affect the stability of DC bus voltage. This paper, through constructing a model of off-grid photovoltaic DC microgrid under impact load characteristics, aiming at the fluctuate problems of the DC bus voltage caused by impact load, puts forward a fast response of hybrid energy-storing system composed of supercapacitors and batteries and superiors peak regulation capability to shave the peak and fill the valley of the microgrid. The researches on the strategy of double closed-loop voltage stabilization of blended energy storage system are made and the shortcomings of the double closed-loop voltage control of voltage and electricity are analyzed. And based on this, the tactics of new and double closed-loop voltage control of inner ring of power and the energy outer ring of DC bus capacitance are put forward and examined by simulation and experiment. The experiments prove that this method can more effectively suppress the influence of the fluctuations of impact load power on the DC bus voltage and further improves the system's stability. [ABSTRACT FROM AUTHOR]

This paper shows the operation of the microgrid using a new adaptive PI controller based operational (control) scheme. The core of the proposed control scheme is the suggested adaptive PI controller. The parameters of the PI controller are adaptively tuned using a variable step-size least mean fourth algorithm with no need for any system model to operate this adaptive controller. The main merit of the proposed scheme is that it stabilizes the magnitude and frequency of the voltage at any loading condition such as variable balanced loads, variable unbalanced loads, and nonlinear loads. The proposed scheme has a simple structure and accurate performance. In addition, the structure of proposed scheme provides a seamless transition toward any loss or reconnection of any inverter in the microgrid. Furthermore, the suggested operational scheme is flexible enough to enable the microgrid to be operative in a grid-connected mode and to transfer from the voltage control mode to power control mode with a smooth transitional procedure. To validate the meritorious performance of the suggested scheme, its performance is compared to similar schemes based on a linear controller (regular PI controller), single-neuron PI controller (adaptive PI controller), recursive least square-support vector machine based PI controller (another adaptive PI controller), and nonlinear controller (sliding mode controller) for different operations of the microgrid. [ABSTRACT FROM AUTHOR]

A new method for synchronous generator static excitation control is proposed in this paper, based on the PI controller and stabilizing feedback action. Compared with the existing solutions, this paper introduces improvements in the system's dynamic performance, robustness, and sensitivity in relation to noise, based on simplified control system structure modification. By introducing the stator voltage stabilizing feedback action, an improved level of dynamic performance is achieved, which also introduces an increased level of robustness. Furthermore, compared with sequential PID and lead-lag compensator based controllers proposed in related standards and technical papers, the system sensitivity in relation to the measurement noise is not compromised, since the differential control action is not included in the proposed controlling structure. The controller design procedure is performed by means of a frequency domain based technique, while its performance is verified by means of simulation and experimental test runs. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

SUMMARY This paper presents detail assessment of the impact of renewable energy type distributed generation operation modes on the voltage stability indices. Most of renewable distributed energy sources are capable of operating in two modes, which are constant voltage and constant power modes. Different simulation results were obtained for voltage stability index (VSI), which serves as indicator of stability. Furthermore, this study has also considered charging station (CS) as a load, that is, gradually increased at the selected bus until the system attains instability state. The persistence of the instability can lead to voltage collapse, and VSI value can give an indication of the collapse as well. In this paper, the concept of active power voltage stability index (P-VSI) is introduced with the aim of predicting the voltage collapse as a result of incremental CS loading in the network. Based on the analysis conducted in radial networks with multiple distributed generation units, the P-VSI gave better indication for the voltage collapse much more than reactive power voltage stability index. The analysis was conducted on 33 bus distribution system. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]