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• A CFD fluid-solid coupling simulation model to study the temperature distribution of stator coils and inverter of an electric scroll compressor was developed and validated. • The temperature distribution of stator coils and inverter under different refrigerant conditions was simulated and analyzed. • The working reliability of stator coils and IGBT modules under the studied refrigeration conditions was checked. • The heat dissipation of IGBT modules and the proportion of heat exchange amount between different parts of compressor housing and suction gas were analyzed. In the electric scroll compressor for vehicle air conditioning, the heat generated by motor and inverter is mainly taken away by suction gas. It is necessary to maintain the working temperature of motor and inverter within a safe range to void overheat or burnout. The temperature distribution of motor and inverter under refrigeration conditions are studied using computational fluid dynamics (CFD) simulation in this paper. At first, a CFD fluid-solid coupling simulation model is developed and verified by temperature measurement experiment. The maximum deviation between the simulated temperature at three points on the compressor housing and the measured results does not exceed ±3°C. Then the velocity and pressure distribution of fluid domain, and the temperature distribution of solid domains including the compressor housing, the stator coils and insulated gate bipolar transistor (IGBT) modules are analyzed. Next, the effects of operation conditions on the maximum working temperature and temperature distribution unevenness of stator coils and IGBT modules are discussed in detail. In addition, the working reliability of IGBT modules under refrigeration conditions is checked and the heat dissipation of IGBT modules is analyzed. [ABSTRACT FROM AUTHOR]

This paper addresses a comprehensive review on various adaptive grid-following inverter control schemes developed for enhancing the power quality in renewable energy generation systems (REGS). The grid interfacing inverter with various adaptive control schemes has been well researched in recent years and their performance has been found with better characteristics compared to the conventional control schemes. Better fundamental component separation (FCS), dc offset rejection, grid synchronization, amplitude tracking, frequency tracking, phase angle estimation, and low complexity are the few silent features of the adaptive-based control schemes. This survey is very useful for researchers who are working on power quality, AC and DC Microgrid, grid-connected inverter control, multilevel inverter, power electronics, and other related research areas to select the suitable controller for grid interfacing inverter. This paper also focuses the power quality issues, basic standards, power quality monitoring schemes, and solutions. Moreover, power quality improvement techniques by using the power quality conditioners with adaptive control schemes are discussed in the paper. Finally, an extensive comparative study of the recently developed control techniques is performed to select a suitable controller in terms of better FCS, dc offset rejection, grid synchronization, amplitude tracking, frequency tracking, phase angle estimation, and low complexity for grid-following inverter in REGS applications. [ABSTRACT FROM AUTHOR]

In an industry, analysis of load disconnection indices is essential to determine the annual economic loss because of the high cost of load interruptions. With the interconnection of PVs in modern industrial networks, this analysis gets more complicated due to controls associated with PV inverters for reactive power support. Hence, the paper proposes a unique method for such analysis that relies on dynamic simulation to calculate load disconnections. The dynamic simulation allows the integration of the voltage tolerance curve of loads and controls associated with PVs making the scenarios more realistic. The indices are determined by employing statistical experiments which account for annual variability of daily solar and load profiles with the least possible runs of dynamic simulation. The proposed method is applied to calculate load disconnection indices for an IEEE 399-1997 industrial distribution system. A comparative analysis of the cost of disconnection under a variety of solar penetration and operation scenarios is presented. Network planners and reliability engineers can potentially utilize the proposed method to identify PV inverter controls, placement, and size effects on the annual load disconnection indices due to voltage sags. • Method for calculation of annual Load loss indices for Industrial distribution network consisting distributed PVs. • Simulation case study on IEEE 399-1997 industrial distribution system. • Analysis showing economic benefit of having distributed PV w.r.t. annual load loss due to voltage sags. [ABSTRACT FROM AUTHOR]

• Detailed modeling of CIGRE-14 bus standard test system along with inverter control scheme (with and without grid code) and protection system is done in PSCAD environment. • The performance of directional relaying schemes (32Q and 67pos,67neg,67zero) are evaluated in the presence of inverter-interfaced renewable energy resources. A comparative study on the performance of the relays is done in the presence of inverter-interfaced renewable energy resources for different fault types and fault resistances. • The interdependencies between the inverter control scheme used and performance of relaying schemes have been analyzed through mathematical analysis and circuit realization of the inverter-interfaced renewable energy resources. • Based on the mathematical analysis and circuit realization, the probable causes of relay failures in the presence of inverter-interfaced renewable energy resources are detailed. • The impact analysis of the dynamic response of the controller on the protective relay settings from the perspective of protection operation time-frame has been attempted. The potential impacts of the inverter-interfaced renewable energy resources (IIRERs) on the performance of sequence-based directional relaying schemes (SBDRS) have been investigated in this paper. The directional overcurrent relays such as 67 POS , 67 NEG , 67 ZERO and 32Q have been considered for the investigation. CIGRE-14 bus system with IIRERs along with detailed modeling of inverter control scheme (with and without grid codes) and SBDRS have been done in the PSCAD environment. The mathematical analysis and circuit realization of the IIRERs have been attempted in the paper. The exclusive fault characteristics exhibited by IIRERs cause the conventional SBDRS to mal-operate. Significant change in levels of sequence currents and angular relationships between sequence voltages and currents during faults contributes to relay's unpredictable behavior. The comparative study based on different fault types, fault resistances and interconnecting transformer connections have also been done. The study reveals the impact of non-generalized angular differences between positive sequence voltage and current at the inverter terminal on performance of 67 POS. It is found that 67 NEG and 32Q mal-operated for all types of unbalanced faults while the 67 ZERO can be utilized for grounded fault with delta-star grounded connection of interconnecting transformer. [ABSTRACT FROM AUTHOR]

This paper presents the vector control of permanent magnet synchronous motor with load dependent voltage source multi-level inverter. The proposed voltage source multi-level inverter produces 9-level three phase balanced output voltage. The inverter switches are triggered in such a way that it can produce 5-level, 7-level, 9-level output voltage. The level of generated output voltage depends on the loading condition of inverter. The proposed inverter is connected to the permanent magnet synchronous motor for improved performance of drive. The concept of vector control has been used for decoupled control of torque and flux components of current; hence the permanent magnet synchronous motor is controlled like separately excited DC motor. The proposed work had been developed in MATLAB/SIMULINK environment and the performance had been investigated with change in load and speed. To show the effectiveness of proposed inverter FFT analysis of stator current, develop output voltage is done and THD is less than 5%. The ripple in electromagnetic torque had been reduced compared to existing methods. Hence it has been observed that overall performance of drive is enhanced. [ABSTRACT FROM AUTHOR]

• Fault-tolerant operation for 15LCHB with a solar photovoltaic system (SPV). • Fault-tolerant (FT) operations have detection and identification. • Differential Annealing Dynamic Optimization and Radial Basis Function Neural Network. • DDAO-RBFNN is separated into fault detection with lessening of SPV. This paper proposes a hybrid approach for fault-tolerant operation in fifteen-level cascaded H-Bridge (15LCHB) inverter with solar photovoltaic system (SPV). Fault-tolerant operation performs two tasks: detection (classification of normal or abnormal) and identification (identification of faults). The proposed intelligent controller is the combination of Differential Annealing Dynamic Optimization (DDAO) and Radial Basis Function Neural Network (RBFNN) named DDAO-RBFNN approach. The major intention of the DDAO-RBFNN approach is separated into fault detection with lessening of complete photovoltaic solar energy conversion system. The proposed system takes into account the failure of the entire autonomous photovoltaic solar conversion process and manages the output voltage (OV) owing to the conditions of partial shading (PS). The collected data set (normal, abnormal) is stored at workstation. RBFNN is utilized to compute the CMI switching pattern that changes the PWM carrier signal. DDAO get the voltage values from RBFNN and evaluates them with the data set, if there is a rate of change of voltage. Any deviation find in the rate of voltage change, it makes a decision based on standard or fault conditions. The proposed system is activated on MATLAB/Simulink working platform, then the efficiency is compared with existing approaches. [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]

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]

• 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]

Power converters often suffer the disturbance from input source or load during operation. The disturbance could cause large overshoot and harmful oscillation and even make the power converter break down. In order to ensure the reliability of the converter, it is necessary to accurate design the dynamic characteristics of a power converter, namely, the settling time and the overshoot. However, there is no quantitative dynamic characteristics design method of power converters so far. In this paper, an eigendecomposition-based (ED) dynamic characteristics design method is firstly proposed for the quantitative dynamic characteristics design of power converters and is employed into a three-phase grid-connected inverter. Then, the control-parameter regions of the three-phase inverter that satisfy the indexes of the settling time and the overshoot are obtained by using the proposed ED dynamic characteristic design method. Finally, the effectiveness and correctness of the proposed ED dynamic characteristics design method is verified by circuit simulation. Therefore, this paper provides an accurate and quantitative dynamic characteristic design method for power converters, which is helpful to improve the reliability of power converters. [ABSTRACT FROM AUTHOR]

• A new model of dust impact on grid-connected PV was proposed. • The dust characterization and effects in Sohar, Oman was investigated. • Experimental validation of the proposed model with the techno-economical evaluation presented. A grid-connected photovoltaic system was tested and investigated for the entire year under desertic weather exhibited. The system contains 1.4 kW PV and 1.7 kW inverter —the data was measured every second and used to model and evaluate the system performance. However, dust is one of the essential parameters that affect grid-connected photovoltaic performance, yield, and profitability. In this paper, a proposed model has been takes into consideration the dust impact on grid-connected photovoltaic performance in a novel way. The outcomes demonstrate that the proposed model precisely anticipated the system performance and validated through experimental results. However, it is found that the photovoltaic, inverter, and performance efficiencies are 10.80%, 94.00%, and 73.00%, respectively. Besides, the average yield factor is 141.39 kWh/kWp, and capacity factor is 19.64%. It concluded that the system productivity in Oman is within the prospected rate. The information in this paper is valuable for investors, researchers, and engineers interested in grid-connected photovoltaic and dust impact in Oman and neighboring countries. [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]

• To present a single-phase T-type cascaded nine-level (TCHB) grid connected inverter. • Comparatively analyse TCHB against other fundamental MLI topologies. • State a novel PWM switching technique with one triangular carrier and eight references. • Provide mathematical modelling of the inverter operation and PWM method. This paper presents the control and application of a single-phase T-type nine-level cascaded H-Bridge (TCHB) multilevel inverter (MLI) topology. This paper focuses on the effectiveness of the TCHB and its control by presenting the inverter operation based on a PI current controller along with a Maximum Power Point Tracking (MPPT) scheme to realize a grid-tied photovoltaic (PV) system and a novel PWM method offering self-balancing at the DC-link capacitors. In order to attain gating signals for power transistors (IGBTs), the TCHB employs a PWM with one triangular carrier signal and eight reference signals. In addition, a mathematical modelling of the PWM method, along with a theoretical explanation of the self-balancing process has also been provided. To prove the effectiveness of the proposed TCHB topological design, it has been comparatively analysed against other fundamental MLI and symmetric CHB topologies. In addition, to corroborate the working of the control and the PV system application, employing TCHB inverter offering nine output voltage levels (±2Vdc, ±2¾Vdc, ±Vdc, ±½Vdc, 0), simulation and hardware results have been presented. [ABSTRACT FROM AUTHOR]

• The dynamic model of different kinds of air-to-water heat pumps is presented. • Single-stage (SSHP), multi-stage (MSHP) and inverter-driven (IDHP) units are considered. • The detailed energy loss modelling linked to on-off cycling is shown. • Heat pump control algorithms can be optimized by means of the developed models. • Cycling losses have a significant influence on SSHPs seasonal energy performance. In this paper, the impact of on-off cycling losses on the seasonal energy performances of three reversible air-to-water heat pumps having equivalent thermal performance at full load but different power modulation capacity is discussed by means of a series of dynamic simulation models. The analysis of the heat pump performance at partial load, the development and comparison of different control algorithms for heat pumps and, finally, the modeling and evaluation of the degradation effect due to the heat pump on-off cycles at partial load conditions are numerically investigated by means of a series of innovative TRNSYS models not available in the software standard library. The models are able to take into account the variation of the heat pump performance at partial load conditions for multi-stage, inverter-driven and single-stage devices. The findings of this paper point out that the energy losses introduced during the start-up transient of the heat pump has a significant impact on the overall energy performance of the system only for single-stage units, which perform on-off cycles during the whole season, with a decrease of the seasonal performance factor (SPF) up to 12%. On the other hand, modulating heat pumps (i.e. multi-stage and inverter-driven units) avoid carrying out on-off cycles and, of course, cycling losses for a significant part of the season according to their enhanced modulation capacity. It is shown how the accurate dynamic simulation of heat pump-based systems is a useful tool for HVAC designers in order to optimize their control system parameters, with the aim to reduce the compressor maximum hourly number of cycles. [ABSTRACT FROM AUTHOR]

The high-level goal of this research work is to enhance solar integration into power distribution grids with a lower cost and less complexity. High penetration levels of solar can lead to power quality issues at the point of interconnection such as flicker and voltage violation. This paper presents a novel Delta-Q approach that determines the most appropriate amount of reactive power support independent of the time step. The proposed scheme is embodied in the solar smart inverters' Volt-VAR control. It concurrently mitigates voltage violation and smoothens the voltage profile in areas where the solar irradiance is highly intermittent. The performance of the proposed control scheme is evaluated on the Typhoon HIL digital twining testbed along with the dSPACE MicroLabBox rapid control prototype unit. The real-time analysis shows the effectiveness of the proposed technique in lowering voltage violations and also mitigating voltage fluctuations. • A novel Volt/VAR control is proposed for smart solar inverter. • The proposed control strategy contributes to power quality enhancement in smart grids. • A digital twining testbed is utilized for validation/verification. • The proposed control scheme brings the cost and complexity down. [ABSTRACT FROM AUTHOR]

• This research presents and investigates the experimental measurements of power quality parameters in-field on 8 kWp PV system connected to the LV distribution network in Electronics Research Institute, Egypt. Also, This research aims to investigate unity power factor and constant reactive power as two different functions of the PV inverter. • Statistical analysis of each harmonic, power factor and total harmonic distortion are analyzed and presented under different loading conditions and two different functions. • The focus is set on the characterization of relationship between current harmonics of PV inverter and voltage harmonics prevailing in the LV system at unity power factor and constant reactive power. • This paper proposes mathematical models in order to characterize current total harmonic distortion and power factor. The accuracy of proposed empirical models was compared with previous research studies and presented the highest accurate results. Since the penetration of photovoltaic (PV) systems in the Low Voltage (LV) distribution network is increasing, the need to characterize and model the effect of these systems on power quality parameters is an up-to-date issue. Also, the reactive power capability of PV inverter should be defined and discussed. This research presents and investigates the experimental measurements of power quality parameters in-field on 8 kWp PV system connected to the LV distribution network in Electronics Research Institute, Egypt. This research aims to investigate unity power factor and constant reactive power functions as two different operation modes of PV inverter based on the measurements at PV inverter output and the grid point without local loads at off days of the governmental building in order to avoid load effects on the PV inverter parameters. Field measurement data were recorded using the power quality analyzer CA8335. Statistical analysis of each harmonic, power factor and total harmonic distortion are analyzed and presented under different loading conditions and two different functions of the PV inverter. The focus is set on the characterization of the relationship between current harmonics of PV inverter and voltage harmonics prevailing in LV system. It is found that the PV inverter presents high current total harmonic distortion levels at power levels below its rated value. This paper proposes mathematical models in order to characterize the current total harmonic distortion and the power factor at two different operation modes. The accuracy of the proposed empirical models was compared with previous research studies and presented the highest accurate results. The presented results are useful for the manufacturer of the tested PV inverter. [ABSTRACT FROM AUTHOR]

Highlights • An advanced controller applied to multilevel converter. • An improved active power filter application. • Compensating Harmonics as well as linear load feeding. • Improved dynamic response behavior while having the previous controllers advantages. • Full Experimental results provided. Abstract Multifunctional DGs and active power filters have become a mature technology in recent years, so in this paper, an optimized current control method for a multilevel converter is proposed. The control method will overcome harmonic current tracking inefficiency of previous control methods in online harmonic compensation applications in microgrids. This control method is applicable for grid-connected inverter-based multi-functional Distributed Generation (DG) converters. It could also be used in active power filter applications which need high-speed reference tracking ability. Having the advantages of current control methods like hysteresis band control, proportional-integral (PI) and proportional-resonant (PR) control methods, the proposed approach overcomes disadvantages of these methods especially in harmonic reference tracking as it will be discussed in detail. The main advantages of this method are the simplicity of implementation, calculation delay compensation and its fast response to changes. The power electronic circuit, operating principles, two-horizon predicted switching states of multilevel inverter, experimental results and applications of this control method will be discussed in the paper. For studying the feasibility of the control method, an experimental prototype is tested in a microgrid platform. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Multi-string PV systems provide several advantages over other topologies. • Asymmetric Cascaded H-bridge (ACHB) inverter is attractive for photovoltaic applications. • Regulation of the dc-link capacitor voltages is the most important problem of the ACHB inverter. • This paper proposes a simple and powerful FS-MPC to control an Asymmetric Cascaded H-Bridge Photovoltaic Inverter. Abstract This paper presents a Finite-Set Model Predictive Control (FS-MPC) method adapted for an Asymmetric and Cascaded H-bridge Photovoltaic inverter (ACHB). This advanced control approach is designed to: Ensure an independent Maximum Power Point Tracking (MPPT), Synthesize at the inverter output a sinusoidal multistep PWM waveform, and provide an output current with unity power factor and low harmonic distortion. ACHB seems to be a perfect candidate for Photovoltaic systems. However, the control of such kind of converters is quite a challenging task. On the other hand, FS-MPC has achieved great popularity due to the ease with which the constraints, nonlinearities, and switching actions can be included in the controller formulation. Classical approach to tune the FS-MPC parameters is not fruitful for an ACHB. In this concern, we propose, new and dynamic, parameters for the FS-MPC algorithm. This approach is evaluated under different operating conditions including robustness tests. Results provide that the proposed FS-MPC method features a great flexibility and control potential. [ABSTRACT FROM AUTHOR]

Abstract Quantum-dot cellular automata (QCA) technology offers the potential option for performing transistor-less calculations at the nanoscale. In this paper, we introduce a new full adder structure using an inverter chain on a single layer. By utilizing the proposed full adder structure, we design and implement a carry save adder and carry look-ahead adder. Some of these techniques like pipeline structures or asynchronous timing becoming more attractive and are gaining more attention than other solutions. This paper mainly focuses on the high circuit density and energy-efficient aspects of QCA circuits. The design exploits the inherent pipeline nature of QCA, which can lead to an enormous reduction in area using an inverter chain since all computations can be computed in a single block. A comparison among our results and typical structures shows that the presented structures outperformed the best existing designs with respect to area, latency, and cell count. Our structures are more suitable elements for realizing complex QCA circuits with very high operating speed. Functional verification and energy consumption analyses were conducted by well known tools. Highlights • Quantum-dot cellular automata (QCA) is a new computing paradigm based on electronic charge configuration • Important fundamental QCA adders such as Carry Save Adder (CSA) and Carry Look Ahead Adder (CLA) based on the proposed Full Adder are proposed • CSA has the advantage of using parallelism to greatly improve computation performance when there are several operands such as multiplication • A CLA improves speed by reducing the amount of time required to determine carry bits. • The design exploits the inherent pipeline nature of QCA, which can lead to an enormous reduction in area using an inverter chain [ABSTRACT FROM AUTHOR]

Highlights • Control of parallel-connected voltage source converters. • Voltage control loop affects synchronous reference frame inverter output impedance. • Mathematical modeling of error in power sharing between parallel inverters. • Designing dq virtual resistive, inductive, and capacitive impedances. • Experiments validate resistive, inductive, and capacitive droop control in dq-RF. Abstract This paper investigates dq -reference-frame (dq -RF) self and cross-coupling output impedances of the islanded voltage source converter (VSC), by considering the controller impacts. The dq -RF impedances for the closed-loop system are designed to exhibit the desired resistive, inductive, or capacitive characteristics, and are employed in the power control of VSC. The effects of these impedances and connecting lines impedances on the power control of islanded parallel connected VSCs, for different impedance characteristics, are also studied. It is shown in this paper that the unbalanced impedance significantly affects the performance and power control of these parallel converters. Besides, virtual impedance based active and reactive power control of the parallel converters in the dq -RF, for resistive, inductive, and capacitive cases, are designed and implemented. The numerical and experimental results verify the analysis presented in this paper about the dq -output impedance and the virtual impedance based power sharing control. [ABSTRACT FROM AUTHOR]

This paper presents the development of methods and mathematical models to determine the DC/AC average efficiency of inverters that allow to optimize estimates of electricity generation of photovoltaic systems. The adaptive hybrid mathematical model of DC/AC average efficiency of inverters of photovoltaic systems proposed in this paper may be composed of three function settings–Linear, Lognormal, and Polynomial–considering the influence of the relative power, which varies with the sizing factor inverter and the DC input voltage. Determining of the average efficiency with a high degree of accuracy guarantees greater reliability in estimating electricity generation of photovoltaic systems. Depending on the specific behavior of each model and topology of inverter, the adaptive hybrid mathematical model determines the fit functions with highest coefficient R 2 , and estimates with accuracy the DC/AC average efficiency that represents the operation and dynamic behavior of the inverters. [ABSTRACT FROM AUTHOR]

This paper describes an approach to compute the maximum value of energy storage systems (ESS) in grid applications under uncertain energy prices. The value obtained is based on an optimal operation (consisting of charge/discharge sequences) of the ESS. In other words, it is the maximum value that may be obtained when the ESS charge/discharge sequence is adapted to the expected operational conditions. To obtain that optimal value, this paper describes a dynamic program approach, with the particularity that the switching decisions are optimized considering an uncertain price evolution and a dynamic calculation of the aging cost. A practical implementation of this approach is proposed, in which the problem is conveniently sliced into matrices corresponding to single decisions. It is shown that such an arrangement, combined with shift and re-indexing operators, provides a fast solution to the optimization problem consisting of a huge number of decision evaluations. The algorithm is then applied to a number of European electricity markets, with a particular focus on arbitrage. The particularities of the algorithm solutions are analyzed, and it is shown that not considering the imperfect foresight and the aging impacts leads to considerable errors in valuing an ESS. [ABSTRACT FROM AUTHOR]

The trend of global energy demand forecasts a continuous increase in the forthcoming years together with a diversification and differentiation of energy sources. In order to ensure the energy systems transition towards a sustainable functioning mode while avoiding early depletion of energy resources, industrial activities need to foster process improvement. Among energy efficient process design methodologies, pinch analysis and exergy analysis are two powerful methods but each one shows drawbacks. This paper introduces a new methodology that uses the Jacobian Matrix of exergy destruction as a mathematical indicator to couple the Pinch and the exergy analysis and overcome their individual limitations. In the proposed approach, exergy analysis is used not only to assess the exergy losses but also to guide the changes needed in industrial processes structures and operating conditions. And while the pinch analysis considers only heat integration, the proposed methodology allows including other recoverable exergy in a process through thermodynamic conversion. In this paper, the guidelines of the methodology are first detailed. When applied on a basic natural gas liquefaction process, the proposed approach will numerically result in a new improved process comparable to the existing, most widely used natural gas liquefaction process. The main advantage of the methodology is time saving compared to holistic operating conditions improvement as in the traditional process design methods and automatic process structure modification leading to better heat integration. [ABSTRACT FROM AUTHOR]

The popularity of multi-level inverters (MLIs) for high power and high voltage applications, is increasing day-by-day. These MLIs are being integrated with the grid for renewable energy extraction like solar photovoltaic (PV) system. The MLI produces a staircase output voltage with low harmonic content and may inject a sinusoidal grid current with improved power factor. Thus, the MLI based grid-tied PV system can operate at the lower switching frequency with reduced filter requirements. This paper presents the various MLIs, their modulation and control techniques for the grid connected applications. A detailed classification of different grid connected Multi-level inverters (GCMLIs) based on the number and arrangement of DC voltage sources is presented. Also, different control techniques and the modulation techniques have been discussed for different MLI based PV systems being interfaced with the utility grid. The thorough comparisons and discussion of different control techniques used in single-phase and three-phase grid-connected MLI is also incorporated in this paper for better understanding and effectiveness of the past-present and future PV system developments. [ABSTRACT FROM AUTHOR]

• To detect islanding, the 4th harmonic is injected into the output current. • A modified Goertzel filter is employed to measure the harmonics of voltage. • The method is robust to variation of load quality factor and resonant frequency. • The impact of reactive power on frequency after islanding is compensated. • The method is fast and detects islanding within two cycles of fundamental frequency. Islanding occurs when a utility-interactive distributed generator (DG) is disconnected from the utility grid and continues to supply power to local loads. This condition has several consequences including damage to the equipment and personnel safety risks. Therefore, it is required by utility interconnection standards for the DG to stop energizing local loads in the case of islanding. In this paper, an active islanding detection method (IDM) based on injecting a disturbance into the phase-locked loop (PLL) of a grid-connected photovoltaic (PV) inverter and monitoring the harmonic components of the point of common coupling (PCC) is proposed. A modified Goertzel algorithm is utilized to detect the injected harmonic which is effective for a wide range of load conditions in terms of load quality factor, resonant frequency, and reactive power. The simulation results in MATLAB/Simulink show that the proposed technique is fast with minimum side effects on power quality features such as output current total harmonic distortion (THD). This method is implemented on a single phase 5 kW grid-tied PV inverter and is tested experimentally. The experimental results verify that the proposed technique is fast with zero non-detection zone (NDZ) which is effective for a variety of load conditions. [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]

• A comprehensive review of MPPT techniques. • Review of high gain resonant soft-switching dc-dc converters. • Review of high gain current-fed dc-dc converters. • Review of multilevel inverters for high solar power generation. Power generated by PV panels is highly vulnerable to uncertain weather conditions, and impedance connected to its terminals. Therefore, to maximize the energy productivity from panels by controlling output impedance, a power electronic converter capable of adopting maximum power point tracking (MPPT) technique is required. This paper includes a comprehensive review of basic and advanced MPPT techniques proposed to address the variations in temperature, irradiance, partial shading conditions. Power processing equipment such as dc/dc converters and inverters are mandatory in extracting power from PV panels and utilizing either for standalone systems or grid integration. Grid integration is a major focus where access to utility line ranging from domestic micro-inverters (<300 W) to solar generation (>MW). A centralized inverter topology interfaces a MW power rating PV farm consisting several parallel strings of series connected PV panels to the grid. This review article contributes on presenting an overview of the state-of-the-art power electronics systems for integration of PV panels to the grid. Various interfacing power electronic architectures covering micro-inverter, central inverter up to modular inverter approach operating at low switching frequency and high switching frequency with resonant and pulse-width modulated (PWM) soft-switching or hard-switching are reported. Various voltage-fed and current-fed multi-level inverters for such architectures are studied and discussed. [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]

This paper presents a novel approach to the modeling and control of AC microgrids that contain spinning machines, power electronic inverters and energy storage devices. The inverters in the system can adjust their frequencies and power angles very quickly, so the modeling focuses on establishing a common reference frequency and angle in the microgrid based on the spinning machines. From this dynamic model, nonlinear Hamiltonian surface shaping and power flow control method is applied and shown to stabilize. From this approach the energy flow in the system is used to show the energy storage device requirements and limitations for the system. This paper first describes the model for a single bus AC microgrid with a Hamiltonian control, then extends this model and control to a more general class of multiple bus AC microgrids. Simulation results demonstrate the efficacy of the approach in stabilizing and optimization of the microgrid. [ABSTRACT FROM AUTHOR]

This paper presents a model with analytical expressions for the jitter of a ring oscillator (RO) caused by single-tone sinusoidal interference on the power supply. The value of the jitter can be calculated given the static delay of the inverter and the size of the RO. The model explains the relationship between the jitter and the interference parameters, such as frequency and amplitude. Transistor-level simulations and test-board measurements are performed. The jitter calculated from the model corresponds well with the experimental results over a wide frequency range. The positions of the local maxima and minima in the frequency response are precisely calculated by the model. The jitter model is applicable even under large-amplitude interference. The unusual negative-growth behavior in the amplitude response predicted by the model is also observed in the experimental results. The traditional linear theory for the jitter of a ring oscillator is based on the assumption of a small signal. The model in this paper is valid for more general cases, as it can be used to explain and predict key features of jitter. [ABSTRACT FROM AUTHOR]

The combination of multilevel inverter with renewable energy source power generation is paid more attention among the researchers, because multilevel inverters are widely accepted power converters in for high-power applications. The conventional multilevel inverters are highly implemented in industries, and the success of this has motivated to create newer topologies with the reduced overall power electronics components. In this paper, recent multilevel inverter topologies with reduced number of switches are taken into account and to find a suitable topology for photovoltaic (PV) and wind energy applications. Finally, this paper gives a pathway for the upcoming researchers to consider the design issues and challenges in the development of new multilevel inverter topologies. [ABSTRACT FROM AUTHOR]

Observing present scarcity of fossil fuel and emissions of greenhouse gases, electricity generated from Renewable Energy (RE) sources turns out to be the best alternative for generating the power. In RE system, the inverter is normally used to condition the DC power into AC to meet the requirements of load and transmission system. The inverter offers myriad benefits; however, the presence of harmonics (particularly low-order) in the output voltage affects the efficiency and performance of inverter, causes switching losses and decreases the lifetime of the system. In last three decades, significant research has been done to develop the efficient control technique for eliminating the unwanted harmonics. The preliminary review of existing control techniques revealed that the selective harmonic elimination pulse-width modulation (SHEPWM) is more proficient to eliminate the low-order harmonics. However, non-linear transcendental equations used in this technique pose a challenge to solve particularly for calculus-based methods. With the advent of powerful and low-cost computers, bio-inspired intelligent algorithms (BIAs) seem to be a better approach for solving these complex equations. This review paper presents the detailed principle operation of nine well-known BIAs and discusses their application in inverters for harmonic elimination (HE). Moreover, different objective functions are also discussed in this paper which is used by the researchers for HE. Additionally, the performance of five renowned BIAs, namely, Imperialist Competitive Algorithm, Particle Swarm Optimization, Differential Evolution, Bee Algorithm and Genetic Algorithm is critically evaluated. Their performance is analyzed in terms of accuracy, computational complexity, convergence speed, and a number of control parameters. The conclusion has been made on the basis of information extracted from the literature and evaluation results with future recommendations. This single paper covers all the essential information regarding HE in inverters, which will help researchers to design the efficient RE conversion system. [ABSTRACT FROM AUTHOR]

This paper characterizes the bidirectional feature of the transformer-based quasi-Z-source inverter (trans-qZSI) obtained by adding a controllable power device to the input of the circuit. Different arising operation modes and states are analysed and an AC small signal model is proposed accordingly. A controller was designed using the proposed model, and an experimental validation platform was implemented. After the computational and experimental model validation, it was analysed how and when bidirectional Z topology benefits from bidirectional feature, apart from obvious inverse power conversion operation. Robustness increase and fault tolerance of the bidirectional trans-qZSI topology were characterized and validated experimentally for different current demand decrease case studies: when an open circuit is produced in one output phase or when the current demand decreases due to normal operation requirements. The paper characterizes and demonstrates, computationally and experimentally, that it is the bidirectional feature that provides the system with the robustness needed to protect against these kind of failures or operation modes. Not having the additional IGBT could cause the system to enter the discontinuous conduction mode (DCM) zone and destabilize the system’s currents and voltages. In that case the voltage is not able to follow the control reference, which could ultimately lead to the destruction of the components. [ABSTRACT FROM AUTHOR]

This paper addresses the control problem of a PV power generating chain such that the maximum power is provided to the grid connected system without the need of any additional module stages. For this purpose, the proposed control system is directly applied to the power inverter using power-MOS switches, for which, a prediction-based model selects the switch state while minimizing the error between actual and predicted power outputs. Obtained predictions are evaluated using a cost function. Attention is paid in this paper to the validation of the proposed control method using one and two steps future predictions. Finally, simulation results are provided to demonstrate the effectiveness of the proposed control methodology. [ABSTRACT FROM AUTHOR]

Numerous countries are trying to reach 100% renewable penetration. Variable renewable energy (VRE), for instance wind and PV, will be the main provider of the future grid. Cost reduction of accelerates the large scale VRE deployment around the world. The efforts to decrease the greenhouse gases are promising on the current remarkable growth of grid-connected photovoltaic (PV) capacity. This paper provides an overview of the presented techniques, standards and grid interface of the PV systems in distribution and transmission level. This paper compares the different review studies which has been published recently and provides an extensive survey on technical specifications of grid connected PV systems. Moreover, the adopted topologies of the converters, a thorough control strategies for grid connected inverters, as well as their applications in PV farms has been studied. This study will help researchers and industry users to establish their research based on connection requirements and compare between different existing technologies. [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]

Soft Computing (SC) methods are emerged as an alternative approach to conventional techniques for Grid connected Photovoltaic (PV) system because of their ability to solve the complex non-linearity problems. Soft Computing (SC) techniques are developed to handle the adverse environmental conditions such as sudden change in temperature and irradiation which are not addressed by conventional methods. The main focus of this paper is to summarize the application of various SC techniques which apply to different stages of a grid connected PV system such as panel reconfiguration, Maximum Power Point Tracking (MPPT) technique in the converter, Harmonic elimination in inverter and islanding detections. Furthermore, the comparison is made on the performance of SC methods based on several conditions, namely convergence, algorithm complexity, real time implementation, System dependency, Periodic tuning and Oscillations around the operating point. It is envisioned that the information provided in this paper is intended to serve as a valuable reference for future research in grid connected PV system. [ABSTRACT FROM AUTHOR]

In order to meet the increasing energy demands of the modern-day world, the shift towards renewable energy has proved to be a viable alternative, as it has significantly reduced reliance on conventional energy resources. Solar energy, in particular, remains one of the best available renewable energy options, as it is abundant, clean and reliable. Owing to the susceptibility of grid-connected photovoltaic (GCPV) system against grid faults, conventionally the PV inverter would disengage from the power grid by utilizing an anti-islanding technique. Nevertheless, many countries have now implemented grid codes (GCs) to secure and regulate the operation of the GCPV systems from exposure to grid faults. Modern advanced technologies have equipped the PV inverters with the low-voltage ride-through (LVRT) capability to address the issue of grid faults and prevent equipment failure, as it develops compliance of the GCPV systems with the GCs. This paper presents an overview of inverter topologies which include the power processing stage, transformer and transformerless inverter, multilevel inverter, soft and hard switching, bidirectional and hybrid inverters. Thereafter, current injection techniques with LVRT control strategy are discussed and examined. Such techniques have been classified under four main categories: the current compensation controls, reactive current injection (RCI), linear current controls and non-linear current controls. In addition, a comparative analysis has been presented, by thoroughly discussing the merits and demerits of these control schemes, based on the performance parameters of complexity, stability, robustness and power quality assessment. [ABSTRACT FROM AUTHOR]

• Transformerless SqZSI with common-ground and minimum leakage current features is an attractive and cost-effective option as a PV microinverter. • SqZSI injects second harmonic and DC components under certain conditions, which is undesirable in terms of published power-quality standards. • The experimental study on power quality improvement of this family of inverters (SqZSI) is currently limited. • Closed-loop compensation methods based on well-known linear control techniques e.g. PI & PR controllers can mitigate extensively the power quality issues. The transformerless single-phase semi-quasi-Z-source inverter (SqZSI) provides several advantages over classical PWM converters. Reduced or eliminated leakage current, high power density, and low cost are important features making this topology an attractive choice for PV micro-inverter applications. Two drawbacks of this topology are DC and second harmonic injection in the output AC port, which in some cases prevent the fulfillment of standard requirements. To alleviate this power quality issue, four novel harmonic mitigation algorithms based on PI and PR controllers are proposed, analyzed, and experimentally verified with the 90 W SqZSI in this paper. Moreover, a modified modulation reference waveform strategy is introduced. Consequently, the converter performance, in terms of total harmonic distortion (THD V) is achieved at about 1.27% under full power load. Also, in this paper, the non-ideal state-space model of the SqZSI with the effect of the equivalent series resistance of inductors is developed and the generation origin of DC and second harmonic component is analyzed based on the obtained model. The achieved results confirms the significant THD reduction by more than 75%, the DC component suppression, the second harmonic mitigation, and the power quality improvement. [ABSTRACT FROM AUTHOR]

• An asymmetrical multilevel inverter with reduced number of components is proposed. • Cascaded operation with binary based isolated sources generates higher output level. • Boost converters regulates the voltages from PV panels using voltage feedback control. • Low switching frequency modulation helps to reduce harmonics and switching losses. In this paper, a new basic structure of asymmetrical multilevel inverter with optimum number of components for photovoltaic (PV) renewable energy system is proposed. The aim is to reduce the number of components required to achieve a high number of output levels compared to older topologies. The inverter configuration comprises of two basic units connected to a packed H-Bridge. Cascaded operation of the inverter configuration is feasible for higher level generation. The magnitudes of the DC sources are selected in binary sequence to maximize the number of output levels. Solar panels with proportional-integral (PI) controlled DC-DC converters are used as the DC sources. The switch modulations are achieved by pre-defined switching angles which are calculated to minimize total harmonic distortion (THD) in the AC output waveforms. This method is used instead of the classic pulse width modulation (PWM) technique to reduce the total switching loss and the required processing power in generating the switching signals. Compared to the conventional multilevel inverter topologies, the proposed inverter is a better choice in terms of the number of components. It also achieves a good balance between the number of components and total blocking voltage. Hence, its installation will require smaller space and cost. Another merit of the proposed topology is that it produces AC output with low THD at high efficiency. The efficacy of the proposed asymmetrical 31-level inverter topology is simulated using MATLAB/Simulink and is further verified through experimental analysis. [ABSTRACT FROM AUTHOR]

• This paper focuses on the grid integration of a large-scale photovoltaic plant through paralleled inverters. • Robust model predictive control is proposed to enhance the power quality. • Optimization approach is used to minimize circulating currents in parallel inverters. • Simulation comparisons with conventional control confirm the superiority of the proposed approach. In this contribution a robust Model Predictive Control (MPC) is proposed to enhance the power quality of a large-scale PV plant connected to the grid through Paralleled Voltage Source Inverters (PVSIs) with common AC and DC buses. Paralleling inverters allow handling high-power export and offer advantages in terms of redundancy which ensure the system reliability. However, due to the physical differences and parameter disparities between the inverters, zero sequence circulating currents will flow through it, which will disturb the performance of the system. Hence, the control goal is to regulate the currents injected into the grid, suppress the zero-sequence circulating current (ZSCC). Consequently, this study proposes an MPC algorithm that is based on optimization approach which allows minimizing circulating currents. In order to show its effectiveness and performance of the proposed control, a comparison with linear PI controller is included. In addition, design control and tuning procedure are detailed. Simulation results show the performance of the proposed controller in ensuring power quality, and suppressing circulating currents. To verify the real-time feasibility of the proposed control scheme, Hardware-In-the-Loop (HIL) setup is carried out with means of Opal-RT and dSPACE rapid prototyping systems. [ABSTRACT FROM AUTHOR]

• Verification can be effective to validate stand-alone solar photovoltaic systems. • Automated verification method can detect design errors better than simulation. • ESBMC can produce better performance and soundness among automated verifiers. With declining costs and increasing performance, the deployment of renewable energy systems is growing faster. In 2017, for the first time, the number of people without access to electricity dropped down below 1 billion, but trends on energy access likewise fall short of global goals. Particular attention is given to stand-alone solar photovoltaic systems in rural areas or where grid extension is unfeasible. Tools to evaluate electrification projects are available, but they are based on simulations that do not cover all aspects of the design-space. Automated verification using model checking has proven to be an effective technique to validate complex (state transition) systems. This paper marks the first application of software model checking to formally verify the design of a stand-alone solar photovoltaic system, including solar panel, charge controller, battery, inverter, and electric load. Our main focus is on the project validation to be carried out just after the system sizing, i.e., prior to buying equipment and deployment, as a safe approach to ensure the intended behavior. Five case studies were used to evaluate this proposed approach and to compare that with specialized simulation tool. Different verification tools were evaluated to compare performance and soundness among automated verifiers. The results reported by our automated verification method and by the simulation tool were compared with data collected from dwellers of the deployed cases, thereby showing the effectiveness of our approach, where specific conditions that lead to failures in a solar photovoltaic system are only detailed by the automated verification method. [ABSTRACT FROM AUTHOR]

• Commutation problem is completely solved in the proposed DAB microinverter. • Proposed microinverter is simpler and requires fewer parts than conventional ones. • Zero-voltage switching of all switches is achieved using simple control algorithm. • With novel structure and control scheme, proposed microinverter has high efficiency. This paper presents a single power-conversion dual-active-bridge (DAB) microinverter with safe commutation and high efficiency for PV power applications. In DAB microinverters, the commutation problem is a crucial issue which must be solved in order to achieve a higher power capability. Owing to its novel circuit structure, the proposed microinverter can provide the commutation path in any switching case, so that it avoids the high voltage spikes from the commutation problem and provides high reliability. Moreover, the proposed microinverter has a circuit structure that is simpler and requires fewer auxiliary circuits compared to conventional DAB microinverters. In addition, the proposed microinverter achieves simple closed-loop current control and zero-voltage-switching turn-on of all switches owing to its control algorithm. Because these advantages are obtained with only a single power-conversion, the proposed microinverter has high efficiency and simple structure with high reliability. The operation principle and commutation issue of the proposed microinverter are theoretically analyzed in detail, and experimentally validated on a 400-W prototype. [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]