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Summary: A novel adaptive invasive weed optimization technique is presented in this paper for harmonics minimization in standalone system based on three‐phase two‐level voltage source inverter. The low switching frequency techniques are preferred to produce good quality waveform and at the same time to reduce the switching losses and device stresses. Nonetheless, the challenging task is to compute the firing angles from the set of highly nonlinear transcendental system of equations. The proposed technique shows faster convergence and capability to compute in wide rage of modulation index. Moreover, multiple solutions also have been obtained in most of the range of modulation index. Various cases have been evaluated and simulation results have been given to validate conceptual results. The closed loop operation and the real‐time implementation of the proposed technique under dynamic operating conditions have been verified for a three‐phase induction motor load using PI controller. The least square regression is used for real‐time implementation of the proposed technique. The TMS320F2812 digital signal processor (DSP) has been employed to generate the pulse width modulated pulses generated from the computational results. The experimental results obtained are in very close concurrence to the computational and simulation results. [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]

In this paper, a balancing control scheme of DC-link capacitor voltages for five-level hybrid T-type (5L-HT) inverters is proposed, where existing auxiliary balancing circuit is eliminated. The 5L-HT inverter has a significant advantage of the reduced number of devices compared with other five-level inverter topologies. However, this inverter requires an auxiliary balancing circuit, which is used to rectify the voltage imbalance at the DC-link capacitors, and thus negates the competitiveness of this topology in terms of device count and converter volume. To eliminate the auxiliary circuit, a carrier-overlapped PWM (COPWM) is applied in place of the conventional level-shifted PWM (LSPWM) to control the neutral-point currents, where the duty ratios of switches are adjusted by PI controllers. As a result, although the THD of the output voltage is rather increased, the cost and volume are saved by 27% and 52%, respectively, for a 1-MW/6.6-kV system. The effectiveness of the proposed balancing control method for the 5L-HT inverter has been verified through the simulation and experimental results for the prototype hardware. [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]

• 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]

A fault current compensation technique is proposed in this paper for resonant grounded power distribution systems in bushfire prone areas. Arc suppression devices with residual current compensation inverters are used to compensate fault currents due to single line‐to‐ground faults in order to mitigate powerline bushfires. The main contribution of this paper is the design of a compensation technique for the T‐type residual current compensation inverter using a non‐singular terminal sliding mode control scheme. The main objective of the proposed scheme is to reduce the fault current and bring its value to a level so that it cannot ignite fires. The proposed controller is designed based on the selection of a sliding surface in a way the singularity problem can be avoided and chattering effects in existing sliding mode controllers can be eliminated. The desired current injection through the residual current compensation inverter is ensured by enforcing the control law into the terminal sliding surface where the control law is determined by satisfying the Lyapunov stability criteria. The performance of the non‐singular terminal sliding mode controller is compared with an integral sliding mode controller by considering different values of fault currents where these values are varied by changing fault resistances. Results for simulation in the software and processor‐in‐loop simulations are verified against operational standards which are essential for mitigating powerline bushfires. This work focuses to design a non‐singular terminal sliding mode controller for the residual current compensation inverter which is used in an arc suppression device to compensate both active and reactive components of the fault current and keeps its value below 0.5 A within 2 s after activating the residual current compensation inverter which is a requirement as per the operational standard. This controller is designed based on the selection of a terminal sliding surface while satisfying the condition for avoiding the singularity problem. [ABSTRACT FROM AUTHOR]

This paper presents a different Finite Control Set – Model Predictive Control (FCS-MPC) for grid-connected three-phase bidirectional power inverters. These are typically used in dc or ac renewable-based microgrids (MGs), where bidirectional operation and fast dynamic response is required. The bidirectional grid-connected inverters are an essential part of MG, which inject energy into the ac grid or demand energy from it. The dynamic behavior of the system is a major concern since the current can suddenly change depending on the hierarchical controller. This paper proposes a different cost function using sliding mode theory, which offers a good dynamic response, reduced computational burden, and a parameter-free control model. The operation principle of the proposed controller is given and evaluated using a Hardware-In-the-Loop (HIL) system, but also experimentally with a 1kW laboratory prototype. The final results demonstrate the advantages of using this approach in grid-connected three-phase bidirectional power inverters in terms of dynamic response and reduced computational burden, making this solution technically attractive and viable. [ABSTRACT FROM AUTHOR]

Grid‐connected Single‐Stage Boost Inverters (SSBI) are extensively being researched in the area of photovoltaic energy conversion systems. Owing to their single‐stage boosting capability, this class of power converters results in higher efficiency and reliability. This power circuit configuration is constituted by two mutually dependent sub‐converters, in that a front‐end quasi‐Z‐source (qZS) part is integrated to a back‐end multilevel inverter (MLI). The MLI provides the shoot‐through state to the qZS, while the qZS provides the pulsating DC input to the MLI. In general, solar photovoltaic inverters suffer from the disadvantage of leakage current that flows from solar panels to the grid/load. This paper introduces a dual quasi‐Z‐source based multilevel inverter, which achieves the following benefits: (a) five‐level output voltage, (b) reactive power capability, (c) shoot‐through immunity, (d) continuous input current, and (e) reduced leakage current based on VDE 0126‐1‐1 standards. In this paper, a modified modulation scheme, which is based on the employment of phase‐disposed and level‐shifted carrier signals, has been used to reduce the leakage current. To reduce the leakage current further, a passive filter is employed to eliminate high frequency variations across the parasitic capacitance. The working principle of the proposed power converter and the effectiveness of the modulation scheme have been validated with simulation studies in both standalone and the grid‐connected mode. Finally, the simulation studies are verified through an experimental prototype of 500 W rating. [ABSTRACT FROM AUTHOR]

Digital twins, a product of new-generation information technology development, allows the physical world to be transformed into a virtual digital space and provide technical support for creating a Metaverse. A key factor in the success of Industry 4.0, the fourth industrial revolution, is the integration of cyber–physical systems into machinery to enable connectivity. The digital twin is a promising solution for addressing the challenges of digitally implementing models and smart manufacturing, as it has been successfully applied for many different infrastructures. Using a digital twin for future electric drive applications can help analyze the interaction and effects between the fast-switching inverter and the electric machine, as well as the system's overall behavior. In this respect, this paper proposes using an Extended Kalman Filter (EKF) digital twin model to accurately estimate the states of a speed sensorless rotor field-oriented controlled induction motor (IM) drive. The accuracy of the state estimation using the EKF depends heavily on the input voltages, which are typically supplied by the inverter. In contrast to previous research that used a low-precision ideal inverter model, this study employs a high-performance EKF observer based on a practical model of the inverter that takes into account the dead-time effects and voltage drops of switching devices. To demonstrate the effectiveness of the EKF digital twinning on the IM drive system, simulations were run using the MATLAB/Simulink software (R2022a), and results are compared with a set of actual data coming from a 4 kW three-phase IM as a physical entity. [ABSTRACT FROM AUTHOR]

Microgrid (MG) bridges different inverter interfaced distributed energy resources (DERs) to operate and control efficiently within a grid. The multi‐master‐slave control strategy can provide robust control of inverter interfaced DERs in close proximity. The role of master DERs is significant in synchronising the slave DERs and reducing the effect of single unit failure. However, faulty master DERs and master side communication failure can also suddenly affect the synchronisation of the slave DERs. Unfortunately, previous studies on multi‐master‐slave MGs have not addressed this issue. So, in this paper, a synch invulnerable multi‐master‐slave control strategy is proposed by introducing a synch selector with the centralised secondary controller. The synch selector is designed to pick the synchronising references from the first available healthy master units while keeping other masters operational and sending the synchronising references to the slave DERs. It also significantly reduced the dependency on communication lines up to the possible extent. Real‐time simulation results are presented to demonstrate the effectiveness of the proposed control strategy. The presented results show that the unhealthy master units seamlessly can be side‐stepped, and the next possible healthy master unit can be assigned to send reference signals to the slave DERs, hence, resisting synch vulnerability. The observations also show accurate power‐sharing, full utilisation of DERs, and reliable and stable operation of the entire MG. [ABSTRACT FROM AUTHOR]

This paper presents the design and development of Modular Multilevel Inverter (MMI) to reduce Total harmonic distortion (THD) using intelligent techniques towards marine applications. Many researchers have described the additional advantage of inverter control challenges such as voltage imbalance, increasing the number of voltage levels, power quality issues, reducing the number of semiconductors switches and achieving higher efficiency. Under the intelligent techniques, the implementation is carried out with aid of Artificial Neural Networks (ANN), Fuzzy Logic Controller (FLC) and Adaptive Neuro-Fuzzy Inference System (ANFIS) to calculate the modulation index (ma) and switching angles (θ) for MMI. Based on the calculation, it is trained to form a mapping between inputs and outputs for obtaining reduced Total Harmonics Distortion (THD). The objective of the intelligent controller is to control the inverter for regulating the output voltage with lowest THD. The proposed control structure has been estimated and compared for better robustness in terms of switching angle and modulation index with least THD in the inverter. Simulations and prototype models are made to analyze the controller's performance, for inverter output voltage and harmonics. This proposed system is designed for marine lighting load application. The FPGA performance with all intelligent methods are analyzed by in SPARTAN3E500 FPGA device. [ABSTRACT FROM AUTHOR]

In photovoltaic (PV) systems, inverters have an essential role in providing an energy supply to meet the demand with power quality. Inverters inject energy into the grid considering that a renewable source is available; however, during intermittent periods or in the absence of power generation, the inverter remains inactive, which decreases the performance of the PV system. One way to increase the operation of inverters is to operate them as Volt-Amps Reactive (VAR) compensators to generate reactive power in the absence of renewable sources. The paper presents the development of a control scheme that allows the PV system's inverter to improve the power factor in the electrical system with or without PV power generation. The proposed control is based on using a sliding mode controller (SMC) current control loop and PI-based voltage control loop. The control scheme is developed in MATLAB/SIMULINK, and for real evaluation, a PV prototype is implemented. The control strategy efficiency is confirmed by the obtained results. The control scheme increases the practical utility of PV systems. Additionally, it improves the power factor in all cases during the injection of active power to the grid operating under intermittent conditions and/or in the absence of power generation. [ABSTRACT FROM AUTHOR]

The unexpected subharmonic oscillation with an evident asymmetric feature is one of the most salient dynamical behaviors in the grid-connected inverter, which will bring disaster to normal system operation. In view of time-varying equilibrium points and complex dynamical response of the system, this asymmetrical subharmonic oscillation is difficult to predict through traditional analysis methods. In this paper, a ripple-based current model is proposed to describe the special subharmonic oscillation of single-phase grid-connected DC–AC inverter with the One-Cycle Compensation (OCC) method. Based on the proposed model, the influence of dynamic response and the time-varying equilibrium points on the stability of the system are comprehensively analyzed, and the internal mechanism of asymmetric subharmonic oscillation is revealed. Furthermore, the critical points of the subharmonic oscillation at the beginning and the end of the whole circuit cycle are predicted. Particularly, a global stable operation boundary is identified from the ripple-based analysis to optimize circuit design. Finally, circuit experiments are performed to verify these numerical and theoretical results. [ABSTRACT FROM AUTHOR]

Access to electricity offers great benefits to development through the provision of reliable and efficient energy sources in the country. Majority of the population living in the remote and rural areas of developing countries mostly sub-Saharan Africa are not supplied with electricity. Although the governments through their electricity companies put their effort to extends the grid distribution networks to remote and rural areas still the coverage were not sufficiently enough due to growing demands for safe and reliable electricity. However, solar as a source of energy remains the least utilized energy source in many countries including Tanzania. Solar Photovoltaic (PV) systems mini-grids have shown their potential in rural electrification projects in many countries mostly sub-Saharan Africa. A solar PV system mini-grid is a PV plant with a localized distribution network to a unit village, or a cluster of villages, providing alternating current (AC). Basically, it consists of solar PV modules of a certain capacity, charger controller, inverters for converting the DC power to AC power, housing for the battery bank and plant control systems. In areas where there is no grid connection or where diesel generation is the main power source, PV plants are able to generate electricity efficiently and relatively cheaply. This paper aims at giving out the overview of solar PV mini-grid applications in Tanzania basically, in terms of technical design and economic analysis of the selected minigrid system at Juma Island village located in Sengerema District in Mwanza Region. The Juma Island settlements has the electricity demands estimated about 25 kWh per day. At the prevailing tariff conditions in the country, this project can be considered as financially viable with feed-in tariff scheme or other incentives such as grants/capital subsidies when applied. However, the other nonfinancial benefits like the greenhouse gas emissions savings can, in the long run, help mitigate the adverse effects of the climate change problem plaguing the entire earth. [ABSTRACT FROM AUTHOR]

This paper presents an adaptive sliding mode control (SMC) method with a variable boundary layer for single-phase voltage source inverters. This strategy offers a very simple sliding function without any derivative term while preserving unique characteristics of the sliding mode control like fast dynamic response and robustness against parameter variations while also possessing the variable boundary layer method to reject the chattering phenomena. Chattering excites the high frequencies in the system and leads to inaccuracy and instability. It is shown that despite the conventinal approches, the proposed variable boundary layer method can both alleviate the chattering and generating the minimum steady state error. Owing to the adaptive nature of the suggested control approach which adjusts the thickness of the boundary layer, the whole mechanism can be controlled successfully under unpredictable parameter variations. The accomplishment of the suggested strategy is investigated by simulations in MATLAB/Simulink. The outcomes are compared with the outcomes obtained without boundary layer, with constant boundary layer and super twisting sliding control methods. The comparison reveals that the proposed control technique outperforms the other control methods for the voltage source inverter. The results demonstrate that while the conventional, SMC with constant boundary layer and super twisting sliding control (STSMC) methods have 50%, 8% and 10% chattering over their control input respectively, the proposed method has less than 3% chattering over the control input. [ABSTRACT FROM AUTHOR]

This paper presents a finite control set model predictive control (FCS-MPC) approach for two induction machines driven by a nine-switch inverter (NSI). In the traditional approach, two separate voltage source inverters are necessary to drive the independent induction motors. In the proposed method, the nine-switch inverter is used to control the separate motors with a reduced number of switching devices compared to traditional method. A robust control strategy that eliminates the interactions between separate mechanical loads is required to achieve a proper independent speed and torque control for two induction machines through the NSI. To ensure the reliability of the machine operation, the indirect-field oriented control-based model predictive control strategy is proposed. The proposed control strategy is experimentally validated across the 3.2 kW SiC-based NSI prototype. The control algorithm is performed on an Altera Cyclone IV Field-programmable gate array. The experimental results demonstrate that the proposed dual-model predictive control method provides a good and robust motor control operation under different loading conditions. Two induction motors are successfully controlled, and the independent speed and torque control are achieved. [ABSTRACT FROM AUTHOR]

Discussed in this study is a bidirectional power control technique for a three-phase grid connected inverter under different unbalanced grid conditions. Prior researchers have focused on either solving the unbalanced problem or controlling the power. However, this paper addresses both issues: solving the unbalanced problems of the point-of-common-coupling (PCC) voltages and grid currents, and reducing the large ripple in the real and reactive power while also applying a bidirectional power control under weak grid conditions. A phase-locked loop (PLL) is not required because a simpler PR controller was employed. A symmetrical components extraction method was used. Compared to previous symmetrical component techniques that used complicated transformations, this approach requires less computations. Since the unbalanced load issue has been resolved, other loads connected to the grid will not be impacted. MATLAB Simulink was used in simulation experiments, and a real-time interface platform dSPACE DS1202 was used to verify the proposed control method efficacy experimentally. [ABSTRACT FROM AUTHOR]

In distributed power generation systems, grid-connected inverters are becoming an attractive means of delivering the energy generated from renewable sources into the grid. However, the performance of the current controller drastically decreases in the presence of model uncertainty, grid harmonics, filter parametric, and grid impedance variations, which can jeopardize the entire system's stability. This paper presents a novel design of a super-twisting integral sliding mode control (ST-ISMC) strategy for the first time in the application of a three-phase voltage source grid-connected inverter. The designed controller has shown robustness and maintains a low total harmonic distortion (THD) in the presence of filter parameters drift, grid impedance variation, and grid harmonics distortion. The super-twisting action is added to remove the chattering problem associated with the conventional SMC strategy, and integral action is adopted to improve the grid's current steady-state error. The modeling and simulation of a complete system are carried out using MATLAB/SIMULINK. Finally, a real-world hardware prototype system is fabricated to demonstrate the performance and effectiveness of the proposed controller. [ABSTRACT FROM AUTHOR]

To identify the parameters of variable flux reluctance machines (VFRMs), the input voltage value is usually obtained from the reference voltage indirectly. However, the reference and actual voltages may be different due to the nonlinearity of the open winding inverter when using zero-sequence current, leading to the inaccuracy of parameter identification. To solve this problem, this paper proposes an equivalent nonlinearity voltage error model of the open winding inverter to compensate for the input voltage of VFRM during the online parameter identification. Since in the proposed method the phase current direction is not required, the calculation time can be reduced. Moreover, in the developed parameter identification model of VFRM the derived equivalent nonlinear voltage error is used to correct the input of the identification model so as to improve the accuracy of parameters. Finally, the experimental results on the prototype VFRM are presented for verification. [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]

The voltage rise problem due to the reverse power flow is one of the main obstacles to expanding the photovoltaic systems (PVSs) in distribution networks. In this paper, a decentralized control method for coordinated control of on-load tap changer (OLTC) transformers and PV inverters, is proposed for the voltage regulation of radial distribution networks. In this method, the allowable voltage range is divided into several zones, and appropriate corrective actions are adaptively taken according to each zone. To reduce the tension on the OLTC, first, the reactive power capability of the PV inverters is employed for the voltage regulation, and if it is insufficient, OLTC is used as the last solution. In this regard, the unused capacity of PV inverters is utilized for the reactive power compensation, considering the grid codes reactive power requirements. Furthermore, decentralized control based on a signaling method is used for coordination between OLTC and PVSs, which eliminates the need for communication links. Finally, the effectiveness of the proposed method is validated by the simulation results for the IEEE 33-bus distribution network, and the impact of different reactive power control methods on the number of OLTC operation is investigated. [ABSTRACT FROM AUTHOR]

In this paper, an adaptive fuzzy sliding-mode control (AFSMC) system is investigated for an islanded inverter to achieve a high-performance power supply. A sliding mode control (SMC) law is designed initially to obtain both the voltage tracking error and the current tracking error of the inverter involved, to realize both the output-voltage regulation and the current protection with global stability. Moreover, to deal with uncertainties in the practical inverter system without the chattering phenomenon, an adaptive fuzzy system embedded with a self-adjustive translation width is developed to replace the switch term of the SMC. In addition, the adaptation laws, derived from the Lyapunov stability theorem, adjust the AFSMC parameters online to guarantee optimal and robust performance. Furthermore, the superior control performance of the proposed AFSMC is verified by a numerical simulation in MATLAB, producing experimental results on the prototype in comparison with the conventional SMC. [ABSTRACT FROM AUTHOR]

In high frequency AC (HFAC) distribution system, the resonant inverter is used to improve power quality and keep the stability of the output AC voltage. Aiming at the problems of poor output power quality and slow transient performance caused by unreasonable filter parameter design and load change during inverter operation, a single-phase H-bridge LCLC resonant inverter based on analog circuit controller implement is introduced in this paper for HFAC power distribution system (PDS). In this study, to design harmonic compensator and analyze the responsiveness of the inverter, it is necessary to analyze the output voltage total harmonic distortion (THD) of LCLC resonant inverter and the performance of the open loop system in detail. On the one hand, a proportional-integral-resonant (PIR) controller is designed to maintain the zero static error of the voltage output and suppress the output voltage THD of LCLC resonant inverter. On the other hand, an integral controller combines with phase-shift modulation (PSM) method is presented to effectively improve the transient performance of resonant inverter and provide the fixed frequency of the output voltage. On the basis of the above, the experimental prototype is implemented with the output AC voltage root mean square of 28 V, and the output voltage frequency for resonant inverter is equal to switching frequency. A rated output power of 130 W experimental platform is built to verify the effectiveness of the theoretical analysis, control strategy, and modulation method. [ABSTRACT FROM AUTHOR]

In this paper, some recently proposed multilevel power converters are investigated for their fault-tolerant capabilities and improved reliability. These reported topologies are generally reduced device multilevel inverter (RD-MLIs) configurations that cannot tolerate switch failures due to absence of redundant states. Present work therefore aims to incorporate open-circuit fault-tolerant capability by adding few redundant states in switching sequences of existing topologies. The work in this paper objectively presents two existing topologies of five-level and seven-level Multi-Level Inverters (MLIs) modified for fault-tolerant (FT) capability against single switch open-circuit (OC) faults. The modification for fault-tolerant feature (FT-MLI) has intrinsic self-voltage balancing capability, low cost and control simplicity. The modified FT-MLI uses multi-carrier sinusoidal pulse-width modulation (SPWM) technique to generate control switching pulses as per desired switching sequences. Simulation and experimental results of these modified FT-MLI topologies under healthy, faulty and post-fault mode are presented and discussed. Experimental results verify the feasibility and effectiveness of these modified FT-MLI topologies which are suitable for safety-critical applications. [ABSTRACT FROM AUTHOR]

Summary: This paper proposes a control scheme to reduce the circulating current in parallel inverters of autonomous microgrid. The proposed scheme is based on adaptive modulation index, which is generated by a controller operating along with conventional voltage‐current‐droop controller. Three‐phase inverters are connected in parallel for increased power capability and reliability. These paralleled inverters share common load in a desired ratio with the help of droop controller. One of the operational challenges in paralleled inverter system is that of circulating current which causes power loss, decreased efficiency, current distortion and reduced life. In order to reduce the circulating current, the reference modulation index is adjusted adaptively through an independent controller. The original modulation index is revised by making proportional adjustment toward voltage and current drop errors. This way, the proposed controller works independently and does not affect the performance of conventional droop controller. The design procedure for the proposed controller based on system modeling is also presented in the paper. The effectiveness of proposed controller is verified through simulation and experimental validation. A comparison of performance with a recently published PID‐based coordinated controller is also presented. The results establish the superiority of proposed scheme for balanced, unbalanced and nonlinear load conditions. [ABSTRACT FROM AUTHOR]

Background: Recent advancements in solar power generation technology have paved the way for a vast number of photovoltaic (PV) systems integration into the grid network. The global installed capacity of rooftop PV systems has already surpassed a 50 GW mark in 2020, while the total installed capacity of all types of PV systems is reaching beyond 500 GW. The influx of distributed PV‐generators must be equipped with sophisticated control to ensure grid stability, especially during grid faults. A devastating grid outage may occur if the grid‐tied PV inverters are not equipped with the "fault‐ride‐through" mechanism. Many countries have already enforced a mandatory grid code which includes a low‐voltage‐ride through requirements for PV‐generators. Aim and Objective: This paper reviews the design of a rooftop PV inverters in the light of low‐voltage‐ride‐through requirements. Materials and Methods: For the implementation of low‐voltage‐ride‐through (LVRT), the design of low‐voltage‐sag detection, grid‐synchronization, filter‐selection, and power‐controllers are examined through simulations and literature survey. LVRT implementation issues are highlighted with an emphasis on the current controller performance during grid sags. Results and Discussion: From the review and analysis conducted in this study, this paper concludes that ensuring a stable DC‐link and appropriate control‐reference‐signals during the grid faults are the keys to the LVRT implementation. Conclusion: In addition to robust power control, an autonomous PV generator should promptly detect the grid conditions and fulfils the ancillary services like LVRT, anti‐islanding and flicker compensation. The recommendations and the future trends in the LVRT research conclude the review article. [ABSTRACT FROM AUTHOR]

This paper deals with the detailed review and comparative analysis of latest reduced switch multilevel inverter topologies for electric vehicle applications. The recent trends in reduced‐switch multilevel inverters are discussed. Detailed review of the reduced‐switch multilevel inverter topologies, their merits and demerits, and the comparative analysis based on component count, total harmonic distortion, and efficiency are conducted. This paper gives a detailed review of recent trends in reduced‐switch multilevel inverter topologies for electric vehicle applications. Switching pattern of the topologies is provided for better understanding of the inverter operation. Comparative analysis of the reduced‐switch inverter topologies based on the component count, total harmonic distortion of output voltage, and efficiency is also presented in this paper. Based on the comparative analysis, it is observed that the interleaved nine‐level flying capacitor multilevel inverter topology achieved the lowest output voltage distortion of 1.6%, which is within the acceptable limits of IEEE 519‐2014 standard. It is observed that the three‐level active neutral point clamped multilevel inverter topology achieved the highest working efficiency of 99.4%. This paper discusses the most recent trends in reduced‐switch multilevel inverters. A comprehensive review of the recent publications and a crisp comparative analysis of the different inverter configurations based on component count, harmonic distortion of output voltage, and efficiency are presented in this paper. [ABSTRACT FROM AUTHOR]

Low-inertia microgrids are prone to large frequency fluctuations due to high penetration of inverter-fed renewable sources. A virtual synchronous machine (VSM) is capable of handling these frequency fluctuations. VSM imparts inertial behaviour in grid-connected inverters with the help of an electric storage device. Most of the reported VSM control schemes use a constant inertia parameter that leads to an inadequate dynamic frequency response. In this paper, a fuzzy controller-based self-adaptive VSM control scheme is proposed. Here, the value of the inertia parameter is decided using fuzzy rules which take the penetration index of renewable energy, frequency deviation and rate-of-change-of-frequency as the input parameters. These rules are formulated with the help of the sample data obtained from simulations done in MATLAB/Simulink, where the inertial parameter is optimized using a genetic algorithm for various cases. The proposed method is validated for solar photovoltaic-fed microgrid test systems using power–hardware-in-the loop and the results indicate a reduction in maximum frequency deviation compared to the constant inertia parameter based VSM schemes. The introduction of renewable energy penetration level and fuzzy expert system in modifying the inertia parameter are the novel contributions in this paper. [ABSTRACT FROM AUTHOR]

This paper proposes a high power density inverter utilizing SiC metal-oxidesemiconductor field-effect transistor (MOSFET) modules and an interstitial via hole (IVH) printed circuit board (PCB) for a motor drive system. The inverter also includes a power circuit, heatsink, cooling fan, gate drive circuit, and DC capacitors. The output power density of the proposed inverter is 81 kW/L. The inverter outputs 37 kW formotor drive applications. To achieve this superior output power density, this paper explains a prototype SiC MOSFETmodule without an antiparallel schottky barrier diode, and a unique multilayer laminate IVH PCB to connect the modules and DC capacitors. This paper describes the experimental results to verify the motor drive performance and the increase in temperature under the rated load operation. [ABSTRACT FROM AUTHOR]

Modularity, efficiency, power quality, and high reliability are the attractive advantages of multilevel inverters (MLIs). But it has limitations in terms of an increased number of semiconductor devices as compared to conventional 2-level inverters. In this paper, a fault-tolerant single-phase 5-level MLI configuration is proposed. The proposed fault-tolerant configuration of the MLI can significantly improve its reliability while maintaining the modularity of its software implementation. Examination, design, and implementing thought for both normal and abnormal operating situations of the proposed MLI are presented in this paper. The feasibility of the proposed fault-tolerant MLI is verified by simulation in MATLAB/Simulink environment and experimental results in a laboratory prototype. [ABSTRACT FROM AUTHOR]

Due to the widespread use of static power converters in various industries and sensitive applications such as ground power units (GPUs), it is essential that the inverters have high reliability. A failure in the inverters can cause undesirable consequences such as; low performance, shutting down the system, and losing the stability of the entire system. On the other hand, in some critical industrial processes with high standstill cost and safety-aspect concerns, such as aircrafts, high reliability, and survivability of the system are very important. Therefore, the use of fault-tolerant (FT) inverters is inevitable in such applications. In this paper, using an FT inverter, the reliability of the GPUs is increased and it results in higher availability and continuous system performance. Furthermore, a simple automatic fault-detection (FD) algorithm is presented by taking the inverter pole voltage as a fault detection parameter. The inverter is analyzed for open-circuit (OC) fault in the switches and the reliability of the FT inverter is compared with the classic inverter. The simulation and experimental results of the 1 kVA converter prototype are presented to confirm the FT inverter performance and the proposed method. [ABSTRACT FROM AUTHOR]

The direct-drive Permanent Magnet Linear Generator (PMLG)-based Ocean Wave Energy Converter (OWEC) generates variable AC voltage, which cannot be directly utilized by the load. This paper presents a two-stage methodology to convert variable AC voltage to a constant amplitude AC voltage. First, a standard rectifier is used to convert variable AC voltage into variable DC voltage. After that, a cascaded buck-boost inverter is employed to achieve the constant frequency AC voltage. Systematic design and circuit analysis, along with working principle and voltage control strategy, are presented. A small scale laboratory prototype of PMLG associated with buck-boost inverter is developed to validate the proposed concept. [ABSTRACT FROM AUTHOR]

Renewable energy sources and technologies have the potential to provide solutions to the longstanding energy problems being faced by developing countries. The renewable energy sources like wind energy, solar energy, geothermal energy, ocean energy, biomass energy and fuel cell technology can be used to overcome energy shortage in India. This paper proposes a modified multi-level inverter (MLI) topology for Hybrid Renewable Energy Sources (HRES) and a design of hybrid solar-wind power generation model with 9-level, 13-level and 17-level inverter topologies. A HRES connected to a modified Cascaded H-Bridge Multi Level Inverter (CHB-MLI) is developed, whose switches are controlled using Artificial Neural Network (ANN) model. The proposed hybrid energy system model consists of 10 Metal Oxide Semiconductor Field Effect Transistors (MOSFETs) that intend to give 17 levels of output voltage. The proposed topology performs effectively with reduced number of components and reduced Total Harmonic Distortion (THD). The performance of the proposed system is analyzed by designing the model in MATLAB/SIMULINK environment. The simulation results of the proposed inverter for the HRES application are compared with the results of the existing topologies to show the effectiveness of the proposed model. [ABSTRACT FROM AUTHOR]

Distributed generators are more expected with the capability to continue supporting power to local critical loads in both intended and unintended islanding conditions, in addition to its house‐keeping functions of grid‐connected condition. With this purpose, this paper proposes a control strategy of single‐phase grid‐connected inverter with both decoupled power control capability for grid‐connected mode and load voltage regulation capability for standalone mode. It also enables automatic voltage regulation on point of common coupling, which enables seamless transfer after islanding occurrence. An impedance model is disclosed to analyze the operation mechanism during transient state, with further investigations on both the effect of system parameters in different modes and the system operating features. Simulation and experimental results are provided to evaluate its effectiveness. [ABSTRACT FROM AUTHOR]

Integration of multilevel inverters with renewable energy sources have been the subject of many research projects. Numerous topologies of multilevel inverters have been investigated for stand-alone and grid-connected PV systems. The high number of switching devices, complexity, large size, voltage imbalance, and high cost are main drawbacks of the conventional topologies. This paper presents a new three-phase, three-port, five-level inverter based on a switched-capacitor circuit for PV applications. Compared to the conventional topologies, the proposed inverter has voltage boosting capability and multilevel operation without using clamping diodes or flying capacitors, simplifying the control algorithms and improving the reliability, efficiency, and lifetime. The presented multilevel inverter offers 25% reduction in power devices counts and 50% reduction in flying capacitors. The proposed inverter solves the capacitor voltage balancing issue of the conventional topologies and achieves the lowest voltage stress, making it suitable for high voltage applications. Additionally, the new topology harnesses the superior features of silicon-carbide devices; hence, a fast-switching speed can be employed to reduce size of the storage elements and output filter requirements. Furthermore, the soft-switching operation is realized to regulate the charging current of the capacitor. The operating principle of the proposed topology is investigated, and its properties are compared to the traditional multilevel inverters. A laboratory prototype was built to validate the effectiveness of the proposed circuit, simulation and experimental results for the proposed inverter are provided. [ABSTRACT FROM AUTHOR]

By developing a robust control strategy based on the differential flatness concept, this paper presents a solution for the bidirectional trajectory tracking task in the "full-bridge Buck inverter–DC motor" system. The robustness of the proposed control is achieved by taking advantage of the differential flatness property related to the mathematical model of the system. The performance of the control, designed via the flatness concept, is verified in two ways. The first is by implementing experimentally the flatness control and proposing different shapes for the desired angular velocity profiles. For this aim, a built prototype of the "full-bridge Buck inverter–DC motor" system, along with Matlab–Simulink and a DS1104 board from dSPACE are used. The second is via simulation results, i.e., by programming the system in closed-loop with the proposed control algorithm through Matlab–Simulink. The experimental and the simulation results are similar, thus demonstrating the effectiveness of the designed robust control even when abrupt electrical variations are considered in the system. [ABSTRACT FROM AUTHOR]

The current world geopolitical state has driven significant interest in expanding influence in the polar regions. In order to develop new trade routes and defense of these areas, specialized ice-capable vessels are needed. Traditional propulsion technology utilized for these vessels has featured diesel and turbo electric drives with cycloconverter based technology used for speed regulation. Cycloconverter technology has the major disadvantage of characteristic output voltage waveforms that are very non-sinusoidal which induce harmonic rich currents with their resulting negative effects on total power factor and efficiency. There is also the potential to induce harmonic currents that may increase heat production in power cables, stressing insulation and reducing overall component life. Furthermore, sensitive loads such as control system power supplies may also be affected. The output waveform of a PWM drive has harmonic content that is both less severe, and more easily analyzed with current modeling tools. There are significant technical challenges that need to be assessed when considering PWM drive deployment in ice-capable vessels. This is due to the severe load torques, and torque variation imposed on propeller blades during ice-milling operations. To the authors' knowledge, an analysis of the behavior of vector-controlled PWM drives to this type of service has not been published in the open literature. This paper presents an initial modeling and simulation study that investigates whether such a PWM drive and associated controller may be effective for ice milling and other operational evolutions for these types of ships. [ABSTRACT FROM AUTHOR]

In this paper, a bidirectional converter with multi-mode control strategies is proposed for a battery energy storage system (BESS). This proposed converter, which is composed of a half-bridge-type dual-active-bridge (HBDAB) converter and an H-bridge inverter, is able to operate the BESS with different power conditions and achieve the DC–AC function for lower input DC voltage applications. For the HBDAB converter, the variable-frequency control (VFC) and phase-shift control (PSC) are both adopted to achieve zero-voltage switching over a wider power range and the battery module balance control capability for BESS, respectively. In addition, the interleaved configuration is used to reduce the current ripple and increase the overall current rating. For the H-bridge inverter, the unipolar control mode (UCM) and totem-pole control mode (TPCM) are adopted to manage the real and reactive current control under different AC grid conditions. The UCM offers a reduction in current ripple for real and reactive power control. The TPCM is able to eliminate switching losses and achieve higher conversion efficiency for pure real power control. Considering applications for battery energy storage systems, the principle of operation and voltage gain analysis are described. Finally, computer simulations and hardware experimental results from a prototype system are presented to verify the performance of the proposed converter with the different control strategies. [ABSTRACT FROM AUTHOR]

In response to the key engineering problems of photovoltaic grid-connected inverter cluster resonance suppression affected by grid-connected inverter impedance, in this paper, a control strategy based on a disturbance observer is proposed to dynamically compensate for the damping coefficient of the controlled system and improve the robustness of the system. First, an engineering mathematical model of a 200 MW photovoltaic inverter cluster is established, and the mechanism of the active damping of the cluster inverter influenced by the disturbance is analyzed. Secondly, the capacitor current feedback is utilized to constitute the virtual damping, and the inverter output impedance is reshaped to suppress the resonance peak. Then, a Kalman filter is used to improve the traditional disturbance observer to accurately detect disturbance of the system during the dynamic process of the cluster inverter so as to better adapt to changes in grid impedance and dynamically compensate for the virtual damping of the cluster resonant system. Finally, the proposed control strategy is verified with respect to a practical PV power station. The experimental results demonstrate the feasibility of the proposed control method. [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]

This paper proposes a new modified buck–boost converter entitled the basic Z‐H8 topology. The modified configuration is composed by adding two dc decoupling and non‐ideal compensation blocks across the dc‐input side of the conventional Z‐H buck converter. These blocks create some benefits such as buck–boost ability and lower stresses and ripples for passive and active elements by up to 50% compared to the traditional Z‐H structure. Moreover, the proposed topology can be used as a dc/dc, dc/ac, or ac/dc converter. Hence, various control techniques based on unipolar PWM and SPWM are proposed for the basic Z‐H8 configuration to act as an inverter. Other valuable advantages are providing galvanic isolation and reducing leakage current by two blocks, which can be extremely useful for photovoltaic (PV) applications. Thus, a grid‐connected single‐stage PV system with a proper model predictive control algorithm is proposed. Despite a continuous voltage on the Z‐H8 inverter output, other benefits of the proposed PV system are tracking the maximum power point, adjusting the injected powers to the grid, and increasing security and reliability. The operating principle of the proposed topologies and control methods are explained in detail with the relevant equations and are confirmed by the simulation and experimental results. [ABSTRACT FROM AUTHOR]

This paper proposes a feedback linearization controller for a grid-following inverter (GFLI) that uses a conventional Phase-Locked Loop (PLL) as the synchronization unit. The proposed controller enhances the GFLI synchronization by expanding the PLL domain of attraction to the whole plane that is limited to a small region around the equilibrium point in a conventional PLL, provided that the grid impedance and voltage are known. Linearizing the overall closed-loop system, the proposed controller provides linear system attributes for the PLL, leading to an infinite domain of attraction and only one equilibrium point. Additionally, a state-feedback controller is integrated within the feedback linearization controller so that it enables the system to have an adjustable dynamic response. Finally, it is shown that the system is robust against parametric uncertainties. The performance of the proposed control design is validated in Matlab/Simulink and experiment. It is verified that the proposed controller expands the domain of attraction and enhances the system dynamic response. [ABSTRACT FROM AUTHOR]

With the rapid development of renewable energy, large amounts of power need to be transmitted to load centers, and series-capacitor compensation (SCC) plays an important role in renewable power transmission. However, it has been pointed out that SCC interacts with inverters and threatens system stability. This paper investigates the influence of SCC on inverter control, and proposes strategies for enhancing system stability based on the instability mechanism. First, the impacts of SCC on inverter current control and synchronization control are analyzed. A current control model is established by a system transfer function, and a synchronization control model focusing on transient stability is established based on the traditional synchronous reference frame phase-locked loop (SRF-PLL). Bode and nonlinear analysis methods are utilized in the stability analysis of both current control and synchronization control. It is found that SCC has little effect on inverter current control. However, it seriously affects synchronization control. SCC reduces the stability range of synchronization control, and causes system instability when there is a large frequency disturbance. In order to improve system stability, two approaches have been proposed. These approaches are optimizing a PI controller, and designing a band-pass filter (BPF) inside the PLL. Finally, simulations and experiments are presented to verify the correctness of theories. [ABSTRACT FROM AUTHOR]

The power calculation is an indispensable element in droop-controlled inverters because the bandwidth of the measured power has a direct impact on the controller performance. This paper proposes a fast and accurate power calculation algorithm based on the combined Second Order Generalized Integrator (SOGI) filters in stationary coordinates for a three-phase system, which takes into consideration the use of nonlinear loads. The power calculation scheme is formed by the two-stage SOGI filters that are employed for obtaining the active and reactive powers required to perform a droop-based inverter operation, respectively. From the two-stage structure, the first SOGI is used as a band-pass filter (BPF) for filtering harmonics and obtaining the fundamental current of the nonlinear load; The second SOGI is used as a low-pass filter (LPF) for extracting the DC-component, which corresponds with the average power. A small-signal model of a two droop-controlled inverters system is built to obtain the dynamical response and stability margin of the system. And compared it with the dynamical behaviour of a standard droop-control method. Next, the proposed power calculation system is designed in order to achieve the same ripple amplitude voltage as that obtained with the standard droop-control method by adjusting the bandwidth gains. Through simulation and hardware in the loop (HIL) validation, the proposed approach presents a faster and more accurate performance when sharing nonlinear loads, and also drives the inverters' output voltage with lower distortion. [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]

The discontinuous conduction mode (DCM) of the inductor current is an effective way to achieve high efficiency and high power density of inverters because it has the advantages of zero-current switching and small inductance of the filter inductor. Although the DCM can operate at a fixed switching frequency, there has been no linear model for realizing high-performance digital control. This paper provides a solution for this problem. Firstly, a linear first-order charge quantity model (CQM) for a DCM inverter with a fixed switching frequency is established, which uses charge quantities output by the inverter bridge as a control variable. Secondly, a direct charge control (DCC) method is proposed, and the design process is significantly simplified. Finally, the performance of the proposed control method is verified by the experiments using a 1 kW prototype, and a high-quality output voltage waveform with a peak efficiency of above 98% was achieved. The proposed method outperforms existing works because the CQM is a first-order linear model that realizes the high-performance digital control and significantly simplifies the design of controller. [ABSTRACT FROM AUTHOR]

This paper aims at resolving problems of harmonic, reactive power and current imbalance. In the process of photovoltaic grid connection, a multi-objective control strategy is proposed, in which the three-phase network controller simultaneously controls the harmonic and realizes the reactive power and current balance. The I P , I q current detection method, which is based on the current reactive power characteristic theory, can detect the compensation current. In order to reduce the measurement error of PLL, a software PLL based on decoupled double synchronous reference coordinate transformation is introduced, and the principle of multi-objective rule of three-stage network inverter is also given. The simulation and test results show that the harmonic distortion rate decreases from 2.57% to 1.10% with the proposed strategy, and the unbalance between reactive power and current is compensated, which verifies the correctness and feasibility of the strategy. [ABSTRACT FROM AUTHOR]

Although the voltage feedforward control based on the point of common coupling (PCC) has been widely studied in the grid‐connected inverters to suppress the harmonics in the grid current, harmonic instability still occurs when the PCC voltage contains a series of background harmonics under weak grid condition. To this end, this paper applies the grid voltage sensed by phasor measurement units instead of the PCC voltage for feedforward. Meanwhile, considering that coupling between the phase‐locked loop (PLL) and the grid impedance would cause instability under weak grid condition, a novel compensation term is introduced to eliminate the negative influence of PLL. In addition, a method to improve the transient response of the system is also proposed so that the cut‐off frequency does not change with the impedance of the grid. By analysing the output impedance of the system, it can be proved that the strategy proposed can effectively improve the stability of the system. The experimental results indicate that the harmonics in the grid current are obviously reduced and the dynamic performance of the system is improved, which verifies the analysis. [ABSTRACT FROM AUTHOR]

The grid-connected inverter is a key device in the renewable energy power generation system and large-scale energy storage system, which the operational stability and reliability are the basis for the efficient and safe application of electrical energy. A real-time fault diagnosis method of a three-phase for grid-connected application combining a mixed logic dynamic (MLD) model and finitecontrol set model predictive control (FCS-MPC) is proposed. This paper not only realizes the open circuit fault diagnosis and location of the switching devices in the main power circuit, but also discusses the threshold issues and post-fault operations. The advantage of the proposed method is that it directly uses the control data and measurement signals of the controller without extra sensors and calculation, which will shorter the fault diagnosis time and occupy less calculation resource of the main processor. Simulation results illustrate the quickness of the fault identification and accurate position with robustness to the interference of the diagnosis method. Finally, the effectiveness of the diagnosis method was verified by a 1500 W experimental prototype in a laboratory. [ABSTRACT FROM AUTHOR]

The min-projection strategy (MPS) is a switching rule with better convergence speed, which can improve the dynamic characteristics of three-phase grid-connected inverters. However, the grid-connected current harmonics of the system are large when the MPS is used directly in the digital control framework due to the limitations of the sampling frequency. To solve this problem, an improved min-projection strategy is proposed in this paper by introducing a zero voltage vector to the control. First, the non-zero voltage vector is selected through the switching law function of the MPS. Then the time occupied by the non-zero voltage vector and the zero voltage vector can be obtained through an error function, which is established by the principle of minimum current error. Finally, the switching signal can be obtained for control, based on the method of duty cycle modulation. This method can realize fast current tracking and current decoupling control, reduce the grid-connected current harmonics, and improve the steady state performance of the system without increasing costs. The effectiveness of the proposed method is verified by simulations and experimental results. [ABSTRACT FROM AUTHOR]