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Inverter is required to operate at both grid-connected and grid-forming mode for microgrid. When an unplanned microgrid disconnecting to grid circumstance happens, the transition will cause severe current shock to system with multi-parallel microgrid inverters. This paper adopts a dynamic virtual resistance-based droop control strategy and small signal analysis method to reduce the current shock, improve the system stability and safety. The large dynamic virtual resistance is added to the control loop when the mode transition event occurs so the shock current is limited. Comparison between the capacitor current feedback for seamless mode transition method and the proposed method is made to prove the validation, and parameters' impact on the system is also analyzed. Results, which are conducted on MATLAB/Simulation and Hardware-in-the-Loop (HIL) experimental platform verify the feasibility of the proposed method in this paper, effectively reduce the current shock by more than 60%. [ABSTRACT FROM AUTHOR]

Multilevel inverters (MIs) are widely used in voltage source inverter applications due to their advantages of high-quality output voltage waveform, low power loss and low voltage stress. Compared with multiple DC source MI (MDCS-MI), single DC source MI (SDCS-MI) needs one DC source. This makes SDCS-MI more simplified and avoid voltage unevenness among multiple sources, which are advantageous in renewable energy (RE) applications. In order to understand SDCS-MI, this paper classifies and compares existing SDCS-MIs according to classical topologies based on isolated and non-isolated construction, summarizes the advantages and limitations of each type of topologies, and briefly introduces various control strategies of SDCS-MI. Finally, this paper discusses the SDCS-MI in RE systems. In addition, the development trend of SDCS-MI is also analyzed in this paper. [ABSTRACT FROM AUTHOR]

Industries using electrical power have a critical and pressing need for improved power quality (PQ). Several important problems have already been identified, such as voltage swell, sag, and harmonics. However, PQ fluctuation issues remain unresolved. A series of active power filters are used to shield delicate loads from PQ related problems. This paper present a low-complexity control technique for voltage compensation using a type of custom power device used with different inverter topologies called Dynamic Voltage Restorer (DVR). In this study, a three-phase Z-Source Inverter-based DVR is employed to reduce voltage disruption, including voltage fluctuation, sag, swell, and harmonics. Error-driven Proportional-Integral-Derivative (PID) controller provides higher PQ performance in terms of voltage augmentation, stabilization, and reduction in harmonic distortion in the distribution system. This strategy keeps the load voltage near or close to the nominal value and addresses many other voltage issues. The gain parameter of a PID controller is tuned using Harris Hawks Optimization (HHO) method. The proposed work is compared with traditional controllers as well as Genetic Algorithm-based PID controllers, and the distortion of total harmonics comparisons are also conducted to show the accuracy of the proposed Z-DVR. To demonstrate the effectiveness of the suggested methodology, it is implemented in MATLAB/Simulink R2020a tool and the results of the mitigated sag, swell fluctuation, and total harmonic distortion (THD) are studied. [ABSTRACT FROM AUTHOR]

Microgrid (MG) is not only undergoing rapid upsurge and an effective combination of distributed generations (DGs)-based renewable energy sources, but it also fulfills a significant function in upgrading grid infrastructure. It is necessary for DGs, during and after any disturbances in the voltage, to stay connected in order to enhance the voltage, most importantly guaranteeing the stability of the power system. In this present context, the behavior of the distributed generations control systems has a significant impact on the MG performance. This paper investigates the effect of different control schemes of the inverter-based DG unit on the stable operation of MG after the occurrence of faults that lead to islanding events. In this paper, an appropriate control strategy is proposed to enhance the fault ride-through of MG. Within the scope of the study, the MG consists of a conventional diesel generator and an inverter-based DG unit. The MG also contains several load types; RLC load as a static load and induction motor as a dynamic load. The MATLAB Simulink is used to model the MG and its inverter control schemes. In order to assure MG stability, the variations of the voltage and frequency are possessed as key references. Results indicate that the control strategies of the inverter have a strong influence on the stability of MG. Moreover, the MG configuration with the proposed FRT resists fault effects for longer durations and this enhances the stability. [ABSTRACT FROM AUTHOR]

This article presents a novel 3-Φ inverter that operates from a single direct current source and is based on the idea of switched-capacitor (SC) techniques. Each phase leg of the proposed topology (PT) consists of eight switches, two capacitors, and a diode. This configuration enables the generation of seven levels (line-to-line) voltage waveforms. The proposed design has several advantages, such as the capacitors' natural balancing, the ability to boost, minimum voltage stresses on the power switches, and fewer switching components. When compared to the conventional two-stage design, single-stage dc–ac power converters with boost capabilities present an intriguing option. This paper introduces a novel boost-type inverter for use in a wide variety of applications, including rolling mills, fans, pumps, maritime appliances, mining, tractions, and more. The study explains the proposed design, principle, control mechanism, and loss analysis in great depth. The advantages of the PT have been demonstrated through comparison with recently published SC topologies. Finally, a 1550-W downscale prototype is used to experimentally verify its viability and performance, with an estimated efficiency of around 96.6%. [ABSTRACT FROM AUTHOR]

The paper deals with the construction design, thermal simulation analysis and cooler control proposal of double three-phase inverter suitable for electric vehicles. It gives a discussion on basic mechanical design and electric topology, both having strong influence on electrothermal operability. The paper also presents the thermal analyses of the converter operated at specified loading profile and gives control possibilities. Finally, the paper presents the cooler control design and demonstrates its functionality. The paper also discusses its impact on the converter lifetime and implementation. [ABSTRACT FROM AUTHOR]

The multilevel voltage-source inverter (VSI) topology of the series multicell converter developed in recent years has led to improved converter performance in terms of power density and efficiency. This converter reduces the voltage constraints between all cells, which results in a lower transmission losses, high switching frequencies and the improvement of the output voltage waveforms. This paper proposes an improved topology of the series multicell inverter which minimizes harmonics, reduces torque ripples and losses in a variable-speed induction motor drive. The flying capacitor multilevel inverter topology based on the classical and modified phase shift pulse width modulation (PSPWM, MPSPWM) techniques are applied in this paper to minimize harmonic distortion at the inverter output. Simulation results are presented for a 2-kW induction motor drive and the results obtained demonstrate reduced harmonics, improved transient responses and reference tracking performance of the voltage in the induction motor and consequently reduced torque ripples. [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]

Under the aspect of decreasing costs for power electronic elements due to mass production, machines with feeding from multiphase inverters can be considered where each slot is activated as a separate phase. The number of IGBT switches is increased, but the current rating of the IGBTs becomes very small, thus reaching the region of cheap mass production elements. Additionally, this allows a smaller capacitor in the intermediate circuit and a mechanical structure of the inverter that can be easily integrated into the machine housing. By this, the often critical du/dt problems can be reduced significantly. In the machine, new features such as an ideal sinusoidal or even rectangular distribution of electric loading and flux density become possible. Moreover, if induction machines with squirrel cage are considered, a rather free adjustment of the pole pitch is possible. In the paper, this approach and its consequences on the performance and the construction of the machine are discussed for an exemplary induction machine. [ABSTRACT FROM AUTHOR]

Transformerless grid-connected inverters for photovoltaic (PV) applications provide several advantages such as reduced cost and volume as well as an increased efficiency. However, the removal of the transformer gives rise to several problems related to leakage currents and electromagnetic interferences (EMI). This paper presents different chaotic unipolar sine-pulse width modulation (C-USPWM) techniques for a transformerless grid-connected PV inverter based on parameter selection. The main objective behind this proposed chaotic modulation technique is to reduce the conducted EMI without worsening the power quality and the common-mode voltage (CMV). The method is validated through numerical simulations and experimental tests carried out on laboratory prototype of an optimized H5 inverter (oH5). The obtained results showed its superiority to the conventional unipolar sine-pulse width modulation (USPWM). We showed also that the appropriate parameter selection of the C-UPSWM could advantageously combine an improved EMI performance and an efficient control, making it possible to deliver a significant reduction of the peaks' amplitudes in the frequency spectrum of the common-mode (CM) voltage. [ABSTRACT FROM AUTHOR]

This paper presents a photovoltaic (PV)-interfaced dual-drive hybrid electric vehicle (PV-DDHEV) based on dual boost three-port DC–DC converter to increase the fuel efficiency of the electric vehicle by increasing the conversion efficiency of the converters. HEV designed with the photovoltaic (PV) power system requires a DC–DC converter to enhance the PV array output voltage to the level demanded by the drive inverters. Normally, the high gain of DC conversion is obtained by connecting two or more DC–DC converters in series with each other. The series connection of the converters reduces the conversion efficiency and increases the cost of the unit. In this paper, a three-port DC–DC converter designed with a two-winding high-frequency transformer is proposed to offer high voltage gain with reduced number of active and passive elements. In addition to this, the power management algorithm incorporated with the proposed PV-DDHEV reduces the power consumption of the drive motor by estimating the drive torque requirement. The MATLAB simulink and experimental prototype results are presented to validate the proposed PV-DDHEV. [ABSTRACT FROM AUTHOR]

This paper proposes a new normalized Huber adaptive control algorithm for shunt compensation. A 5-level cascaded multilevel inverter (CHB-MLI) is controlled as a shunt active power filter (SAPF) unit for a medium voltage distribution system. The proposed algorithm is designed, modelled, and tested to control the SAPF unit under normal and distorted grid conditions. It is employed to extract the fundamental active power component of load current. This extracted effective component is used to generate source reference currents by multiplying with the unit vector template. Furthermore, the switching of CHB-MLI is performed using phase-shifted PWM scheme. The algorithm helps to mitigate the reactive power and unwanted harmonics generated by the nonlinear load. A single-phase scale-down prototype model is developed for experimental investigation and testing purpose in the laboratory. The associated voltage and current sensors and control circuits are controlled by the dSpace 1104 digital microprocessor. Simulation and experimental results show good performance of the proposed algorithm in steady-state and dynamic load conditions. A fair performance comparison is also done with other conventional adaptive algorithms. [ABSTRACT FROM AUTHOR]

In this paper, a proton exchange membrane PEM fuel cell power plant is used to improve the filtering performance of the conventional active power filter, as well as simultaneously contribute with the electric grid to supply the power to the load. The five-level inverter is used as a shunt active power filter, taking advantages of the multilevel inverter such as low harmonic distortion and reduced switching losses. It is capable of compensating power factor, current harmonics and can also make the interface between renewable energy sources and the electric grid, injecting the energy generated by PEM fuel cell to the load. The active power filter control strategy is based on the use of self tuning filters for reference current generation and a fuzzy logic current controller. The MATLAB Fuzzy Logic Toolbox is used for implementing the fuzzy logic control algorithm. The obtained results show that the PEM fuel cell contributes successfully to supply simultaneously the load with the electric grid and produced a sinusoidal supply current with low harmonic distortion and in phase with the line voltage. [ABSTRACT FROM AUTHOR]

This paper presents a novel high multilevel inverter topology which is based on the created DC voltage levels at loads of the inverter. The circuit model is demonstrated by explaining the relationship between switches, sources and loads. According to the proposed inverter topology, the number of power switches connected to negative side of DC source is constant on inverter, while the number of power switches connected to positive side of DC sources is increasing. Therefore, linear pulse-width modulation (LPWM) is described for operating switches after pulse-width modulation method is developed to generate the PWM signals. Then, mathematical equations are given when resistive ( R), inductive ( L) and capacitive ( C) loads are connected in series on a 9-level inverter. Finally, the performances of the proposed inverters are observed through MATLAB/SIMULINK simulations after the designed multilevel inverters are simulated. So, 6-level, 9-level and 11-level inverters are compared with voltages, currents and harmonic distortions. Harmonic distortions reduce with increasing level of inverter, while three multilevel inverters are investigated on different modulation indexes. The results demonstrate the satisfactory performance of the inverter and verify the effectiveness of a novel high multilevel inverter topology. [ABSTRACT FROM AUTHOR]

Increasing penetration of photovoltaic power plants (PVPPs) to the electrical grid leads to continuous evaluation of grid interconnection requirements. For this purpose, Malaysian grid representative from Tenaga Nasional Berhad (TNB) issued technical rules and requirements concerning the connection of photovoltaic system to low and medium voltage networks. The objective of this paper is to design a large-scale PV plant connected to the MV side of the Malaysian grid, taking the compliance of TNB technical regulations into consideration. In this study, the PV plant has been modeled using MATLAB/Simulink with nominal rated peak power of 1.5 MW. The sizing of suggested PV system is achieved in which the simulation results matched the sizing calculation results. The paper focuses on the model’s ability to reflect the important requirements that a PVPP should have based on TNB rules for MV connection. The results show that the proposed PVPP is compatible with TNB requirements. [ABSTRACT FROM AUTHOR]

This paper discusses a converter structure appropriate for charging the batteries of an electric vehicle. The structure is obtained by a transformation of a conventional three-phase inverter, which is already present in an electric vehicle’s powertrain system. Since the motor inverter’s semiconductor components and the electric motor’s windings form the battery charger’s circuit, a reduction in the powertrain system’s size and weight is achievable. The proposed fully integrated battery charger can operate in buck and boost modes, while providing power-factor correction capability continuously. This paper also proposes an input current control strategy which ensures smooth operating mode transitions, which occur during the operation of the battery charger. The control is entirely implemented within a microcontroller and ensures operation with a high power factor and low total harmonic distortion of the input current. The performance of the discussed converter using the proposed control scheme was verified experimentally. [ABSTRACT FROM AUTHOR]

The aim of the present paper is to show the impact of the feed of multiphase induction machines by a voltage inverter which produces circulating harmonic currents. To eliminate this extra harmonic currents of stator windings that cause losses, a space vector PWM control strategy is employed and developed, based on the vector space decomposition for double-star induction machine modeling, while taking into account the stator mutual leakage between two stars. The simulation results illustrate the validity and efficiency of the proposed model. [ABSTRACT FROM AUTHOR]

The advancement of multilevel inverters has led to an increase in efficiency and reliability. This paper demonstrates the design and implementation of a reduced switch extendable-level inverter-fed open-end winding permanent magnet synchronous motor (PMSM) drive. Unlike traditional multilevel inverter topologies, output voltage levels in the proposed inverter depend on the operating frequency of the switches. As the frequency of operation is very high, the levels in the output voltage reach infinity and hence the term extendable-level inverter. It achieves infinite voltage output levels, with a reduced component count. The configuration of the open-end winding enables the application of the AC voltage directly to the independent motor phases and hence achieves the merits of operation at a reduced input DC voltage. The proposed drive achieves a very high DC-link voltage utilization, reduced inverter switching losses, enhanced power quality, and excellent dynamic response using a single DC source and a minimum number of components. A comparative analysis of the proposed drive with different MLI-fed OEWPMSM drives in terms of the component count and total harmonic distortion is provided. FPGA-based improved sinusoidal PWM control of the proposed drive reduces execution time and enhances the control performance of the inverter. Dynamic characteristics of the proposed drive are provided for analyzing the dynamic response of the drive to a step change in load torque. The proposed drive is simulated using MATLAB/Simulink platform for theoretical analysis and evaluation. The experimental prototype is designed and implemented for validating the proposed drive operation. [ABSTRACT FROM AUTHOR]

Multilevel inverters became a key piece in most energy conversion, transportation and management systems. The present paper encompasses a wide total harmonic distortion (THD) investigation of the multilevel inverter output voltages. Such investigation is conducted with cascaded topology for some reasonable number of inverter levels L and various modulation index m. A novel and efficient approach is developed to express analytically the voltage THD bounds. Found upper and lower THD limits for arbitrary L and m apply also for neutral point clamped and flying capacitor topologies. They could really serve as reference for quality analysis of multilevel inverters. [ABSTRACT FROM AUTHOR]

Shunt active power filters (SAPFs) have been widely used to improve power quality of the grid by mitigating harmonics injected from nonlinear loads. This paper presents a new method for improving the performance of SAPFs using neutral-point-clamped (NPC) three-level inverters. NPC three-level inverters often suffer excessive voltage fluctuations at the neutral-point of DC-link capacitors, which may damage switching devices and cause additional high harmonic distortion of the output voltage. In order to solve the problem, two compensating schemes are proposed to restrict voltage fluctuation in the inverters. The first is voltage dependent, adopting a voltage compensation method, while the second is current dependent, using a current compensation method. The paper describes the respective circuit architectures and principles of operation. Corresponding models are mathematically formulated and evaluated under typical balanced and unbalanced working load conditions. The results show that both schemes are able to alleviate considerably voltage oscillations and hence harmonic distortions, and the current-compensated NPC inverter outperforms the voltage-compensated NPC inverter. Consequently, it is shown that the proposed approaches are effective and feasible for improving power quality of the grid when connected to nonlinear loads. [ABSTRACT FROM AUTHOR]

In this paper, an implementation of the control and the synchronization algorithms for a voltage source inverter (VSI) used in a grid-connected structure is carried out. The main purpose is to show the combined operation of the control and synchronization algorithm for achieving the proper behavior of the grid inverter for the single-phase utility grid system. In order to obtain a proper functionality of the system during perturbation, a proportional integral controller structure along with second-order generalized integrator phase-locked loop is designed and used as synchronization algorithm. Another aim is to control power factor at grid, to feed power into the grid and to decrease phase current distortion of VSI. Secondly, the design of the output LCL filter is proposed in this paper. The results of simulations of the inverter system connected to grid (220 V, 50 Hz) using MATLAB/Simulink are also shown. Simulation results confirm that the grid input power factor is nearly one and the distortion of phase current of the proposed system is reduced, causing the total harmonic distortion for various power conditions falls within 5%. The last chapter shows the experimental verifications of the proposed control algorithm. [ABSTRACT FROM AUTHOR]

The quality of power is always a concern for the high penetration of a grid-connected solar photovoltaic (PV) system due to the variation in solar irradiation and the temperature change of solar output, which in turn varies the fundamental component of power delivered to the grid. A solar source requires an inverter interface to supply the AC load as well as for the grid interconnection. Any reduction in the fundamental component generated by solar PV at a lower irradiation level or at high- temperature results in increasing %THD at the output of inverter for a given fixed switching frequency since harmonics due to PWM technique is comparable with the fundamental component. The selection of high-fixed-switching-frequency PWM reduces harmonics but increases the stress on switches and switching losses. It also suffers from issues of harmonics at carrier frequency and its sideband at multiples of switching frequency that causes acoustic noise and EMI. The random frequency PWM (Random PWM) method overcomes these issues presented by the fixed-frequency PWM method. However, a wide band of Random PWM makes the inverter filter design difficult and causes resonance in the distribution system. In addition, asymmetry in the carrier wave introduces even-order harmonics in the line current. Hence, this paper proposes a narrowband random frequency PWM method to reduce sideband harmonics, lower-order harmonics, even-order harmonics and a total harmonic distortion (THD) for a solar-based grid-connected inverter. Simulation results present a satisfactory performance of the proposed control technique for a steady-state and transient results. Experimental validation of the same is carried out on the OPAL-RT OP4500-based laboratory prototype of a 2-kVA inverter which depicts reduction in harmonics and hence improvement in power quality. [ABSTRACT FROM AUTHOR]

In this paper, SHE based on Newton–Raphson algorithm is used for open-loop control of flying capacitor multilevel inverter. Without measuring current and capacitor voltages, as well as not using any controller and voltage feedback, proposed control strategy generates accurate switching angles, capable of balancing flying capacitor voltage and eliminates lower order harmonics while considering load power factor variation. Efficiency and robustness of proposed algorithm are verified by simulation and experiments. Results show that proposed method does effectively eliminate specific low-order harmonics, and inverter output voltage is resulted in low total harmonic distortion with desired number of levels and balanced capacitor voltages. [ABSTRACT FROM AUTHOR]

An indirect field oriented control of a double star induction motor drive with a conventional PI and fuzzy logic controller based on four rules is presented in this paper. To realize a control of this motor, a DC supply and a PWM voltage source inverter (VSI) are introduced. Performance of the proposed control schemes under load disturbances and parameter variations is studied through simulations. The simulation results regarding the speed response with both controllers are presented and discussed. [ABSTRACT FROM AUTHOR]

The increasing participation of wind turbines based on doubly fed induction generator (DFIG) in the power system around the world is motivating the investigation of novel strategies to enhance the reliability of DFIG and power system connection. This paper proposes the use of a new hybrid multilevel back-to-back converter on DFIG wind turbine to improve its fault ride-through capability and power system transient stability. The proposed topology is built adding single-phase full-bridge inverters in series with each phase of traditional three-phase inverter. This converter is able to generate higher voltages in rotor circuit whenever it is required, which can effectively protect power converter and at the same time contribute with grid transient performance. Simulation results, using PSCAD®, are presented for a 2 MW DFIG machine submitted to symmetrical faults in single machine—infinite bus and three-bus system. Results show that the proposal is effective as a protection and works well as an alternative to traditional solutions, limiting currents and maintaining power control during voltage dips. It is also effective in contribution with the improvement of transient stability margin by the possibility of reactive power injection. [ABSTRACT FROM AUTHOR]

Transformerless inverters are prone to irregular voltage profiles, high harmonics and isolation problems while operating with photovoltaic systems and varying load conditions under stand-alone mode. The aim of the paper is to identify the drawbacks of transformerless inverters operating in stand-alone mode and to propose a new topology with improved performance and control. Further, an intelligent controller is designed to operate the proposed topology with various loads and varying load conditions. The developed controller achieves voltage regulation and low total harmonic distortion for the proposed topology when simulated under MATLAB/Simulink environment. Further, a laboratory prototype of the proposed inverter operating under stand-alone photovoltaic application is developed and operated with the developed control method. The proposed topology along with the developed controller achieves output voltage regulation and reduced THD under varying load conditions. The THD of the proposed system while operating with constant load is observed to be 1.8%, and for varying load condition, it is around 2.12%. Further, the efficiency and power loss of the system are calculated, and it is observed the system exhibits 98.5% efficiency. The achieved results are better when compared with existing work. [ABSTRACT FROM AUTHOR]

This paper proposes an inverter scheme to generate an additional third-harmonic component alongside the fundamental component of the current. The generated third-harmonic component is used to achieve the brushless operation in a wound field synchronous machine (WFSM). Contrary to the traditional schemes used, i.e., dual inverter, single inverter with extra switches schemes, and single inverter with four transistor legs, the proposed scheme comprises a single inverter with three transistor legs that utilizes a modified third-harmonic injection pulse-width modulation. The brushless operation in WFSM requires two windings on the rotor periphery, i.e., harmonic winding and field winding that are interconnected through a rotating diode bridge rectifier. To maximize the usage of generated third-harmonic component, the selection of pole–slot combinations of the machine is carried out considering the winding factors. The proposed inverter scheme is verified in MATLAB, and a 2-D finite element analysis is used to validate the brushless operation of the machine along with its electromagnetic performance. [ABSTRACT FROM AUTHOR]

In this paper, a digital current control of a three-phase four-leg inverter based on predictive cost function is studied. Inverters are important for power electronics applications in three-phase four-wire systems, such as active power filters and uninterruptible power supplies. There are many methods for control of inverters, such as pulse-width modulation and three-dimensional space vector modulation. These methods are complex. In this paper, a simple way for current control of a three-phase four-leg inverter is presented. Here, by using a predictive cost function and fixed-point computations, the optimal switching state to be applied in the next sampling is selected. Finally, to evaluate the accuracy of the fixed-point computations, several cases for balanced and unbalanced loading conditions are verified. In each case, the parameter that measured to confirm computation accuracy is total harmonic distortion. [ABSTRACT FROM AUTHOR]

In this paper, a new and efficient global optimization method known as teaching-learning-based optimization is adopted to optimally design the parameters of a passive RC-damped LCL filter for grid-connected voltage source inverters. The novel proposed objective function of the optimization algorithm is to minimize the values of inductors and capacitors. The proposed design improves inverter efficiency and minimizes filter stored energy at a predefined operating and switching frequencies. Moreover, the proposed design procedure may reduce the complexity of the passive RC-damped LCL filter by removing one inductor or one capacitor. The optimal design procedure is built based on an accurate mathematical model and description of the filter topology. A detailed comparison between the results of the proposed work and related work in the literature is thoroughly discussed. The optimized filter is designed, built, and validated analytically and experimentally for verification based on a hardware prototype. [ABSTRACT FROM AUTHOR]

To reach the increasing demand for power quality and power rating along with lower harmonic distortion and lesser electromagnetic interference, the multilevel inverter is needed. Solar energy is one of the favorable renewable energy resources, and the multilevel inverter has been proven to be one of the important enabling technologies in photovoltaic utilization. This paper is based on the study of behavior of a nine levels NPC three-phase inverter topology interfacing multistring photovoltaic system to the electric grid. This inverter is controlled by the pulse-width modulated strategy. Eight carrier waves of the same frequency and different amplitudes are compared with two references (a sine wave and its opposite) for generating the control signals of the switches. Some DC/DC boost converters are used to amplify the voltage produced by the photovoltaic generators. Each of these converters is controlled by a fuzzy Logic-based maximum power point tracking algorithm (FLBMPPTA) in order to track the maximum power point of the GPV; results of simulation in Matlab environment are given and discussed. [ABSTRACT FROM AUTHOR]

This paper aims to study the performances of the dual open-end stator winding asynchronous machine with 0∘ shifting supplied by two 2-level cascaded inverters. To establish this study, the effects of shifting in both cases 0∘ and 30∘ are analyzed, when the machine is fed by four classical inverters (two 2-level inverters for each winding input). The obtained simulation results prove that with 30∘, the machine offers good torque quality but decreases the quality of phase current. To overcome this limitation, the dual open-end stator winding machine at 0∘ is supplied by four multilevel converters. Each converter is constituted by two 2-level classical inverters in cascading. This structure allows to increase the number of levels of the voltage and to improve the electromagnetic torque while providing better current quality in the stator. The obtained simulation results for the two shifts and for the two used converters confirm the important advantage of the association of this machine at zero shift with two 2-level classical inverters in cascading. [ABSTRACT FROM AUTHOR]

This paper proposes a new topology for a brushless wound rotor synchronous machine (BL-WRSM) using a specially designed stator winding supplied through a single three-phase inverter. In this topology, a special stator winding, which comprises of two sets of series-connected windings with an unequal number of turns, is used to generate an additional spatial sub-harmonic component in the stator magneto-motive force (MMF). This additional sub-harmonic MMF (SH-MMF) component is utilized for exciting the field winding of the BL-WRSM. The advantage of the proposed brushless topology is the use of a single inverter compared to a dual inverter used in the existing dual inverter BL-WRSM. For the rotor, there are two separate windings: (1) harmonic winding and (2) field winding. Both the harmonic and field windings are connected in parallel with each other through a rotating rectifier. The additional SH-MMF component generates a rotating air-gap magnetic field, which induces the voltage in the harmonic winding. This induced voltage is then rectified and used to supply a dc current to the field winding. A 2-D finite element analysis is performed to analyze and verify the operating principle of this new BL-WRSM. [ABSTRACT FROM AUTHOR]

This paper presents a hardware description methodology for the direct torque control (DTC) of a three-level voltage source inverter (VSI) fed a permanent magnet synchronous motor drive with neutral-point balancing control algorithm based on field programmable gate array (FPGA). The main drawback of the conventional DTC during its digital implementation is the high torque ripple, and to overcome this problem, the use of a three-level VSI and a simple hardware description methodology for DTC based on FPGA is proposed. However, the circuit limitations of the three-level inverter, such as neutral-point balance, should be taken into account in the selection of the future space vector applied to the machine; for this reason, a simple and effective procedure to maintain the neutral-point balance is presented. The proposed methodology has been validated using hardware in the loop simulation, and results under different operating points are presented. [ABSTRACT FROM AUTHOR]

In this paper, a new control strategy for zero-current transition technique is suggested to constant voltage constant frequency sinusoidal PWM inverter. This strategy consists of a resonant arm and auxiliary switches, which are connected to a standard single-phase full-bridge voltage source inverter and also to a proportional integral voltage controller. The main and auxiliary switches can be separately controlled. The suggested strategy is able to reduce switching losses successfully, and also it does not need any snubber circuit. By using appropriate switching algorithms, the strategy can be applied to uninterruptible power supplies, photovoltaic systems and DC/AC inverters as well. In this study, not only the theoretical analysis but the simulations of the suggested strategy have been carried out effectively. From the simulation results, it has been shown that the suggested strategy yields 30% less switching losses and has better performance when compared with the hard switching strategy for the same operating condition, including the conditions of the load and the switching frequency. Eventually, the suggested control scheme verified by the simulation results proves that it can achieve low THD values in addition to less switching losses. [ABSTRACT FROM AUTHOR]

A power distribution system operates most efficiently with voltage deviations along a feeder kept to a minimum and must ensure all voltages remain within specified limits. Recently with the increased integration of photovoltaics, the variable power output has led to increased voltage fluctuations and violation of operating limits. This paper proposes an optimization model based on a recently developed heuristic search method, grey wolf optimization, to coordinate the various distribution controllers. Several different case studies on IEEE 33 and 69 bus test systems modified by including tap changing transformers, capacitors and photovoltaic solar panels are performed. Simulation results are compared to two other heuristic-based optimization methods: harmony search and differential evolution. The simulation results show the effectiveness of the method and indicate the usage of reactive power outputs of PVs facilitates better voltage magnitude profile. [ABSTRACT FROM AUTHOR]

In the paper, Step sinus pulse width modulation (SSPWM) three phase inverter is tested on a nonlinear device which can produce harmonics. There are 12 switches on active and passive cases. On the inverter, operations of switches are provided by arranged SSPWM which can be calculated with similarity rules of triangles. A mathematical model of inverter is obtained with operating characteristics of the switches determined. SSPWM technique is used to control non-linear devices as thyristor and rectifiers which are widely used in electronic systems. So, single phase alternating voltage is converted to direct voltage with rectifier circuit to provide input voltage of inverter. After that, Six switches of common three phase inverter model are connected to six thyristors controlling inputs and outputs of three phase loads so that performance of SSPWM can be investigated on high level harmonic of loads. The inverter load of resistive (R) and inductive (L) are performed at the MATLAB Simulink so that SSPWM technique could be showed the reducing effect of the harmonic on loads. So, SSPWM and SPWM controlling inverter are performed on frequencies. Then, performances of common SPWM and SSPWM running nonlinear loads are compared with results. [ABSTRACT FROM AUTHOR]

The paper presents an analysis of a hybrid 13-level inverter, which consists of three cascaded H-bridges per phase. Each H-bridge produces 5-level voltages. The proposed approach can be extended to any desired number of levels. Extensive simulation results of the proposed inverter are presented. Several aspects as total harmonic distortion factor of the inverter output currents, and voltages, harmonic content, frequency spectrum distribution, and switching power losses are studied to determine an optimal operation point of the inverter. The simulations are validated by hardware-in-the-loop experimental results. [ABSTRACT FROM AUTHOR]

This study presents a new single-phase transformer-less grid-connected inverter based on a six-phase interleaved dc/dc converter as a suitable topology for PV applications. The proposed topology consists of a dc input and multi-output in the dc-link side which results in production of six levels per half cycle. The voltage of the inverter at output side is 7-level that is injected into the network. The voltage of PV panels is low and this problem is solved by increasing the voltage level in the interleaved converter. Besides, the input current ripple of the interleaved dc/dc converter is very low which causes to improve the quality of the injected current into the grid through a PV panel. For control of the power switches and active/reactive power flows, the model predictive control (MPC) method is applied. The proposed system is capable of creating different voltage levels in step-up/down at the dc-link side and this will make it suitable for working in a wide range of power in the grid-tied. Besides, the total voltage blocking (TVB) of the power switches at the inverter side is greatly decreased. Consequently, the efficiency of the proposed system is high. To prove the accuracy of theoretical calculations, the proposed topology for a 900 W prototype at an operation of 50 Hz is built and tested in the laboratory. [ABSTRACT FROM AUTHOR]

Fossil fuels will eventually be phased out because they are unsustainable, and their combustion releases harmful pollutants. Therefore, renewable energy sources (RES) are used instead of fossil fuels to generate electricity. The most important aspect of RES is its unlimited and infinite supply. In addition, the RES, including wind, solar, geothermal, tidal, hydroelectric, and others, offers clean, environmentally favorable energy sources. Photovoltaic (PV) systems are widely used in power systems due to their accessibility and low maintenance requirements. Solar energy is abundant and produces clean energy compared to other renewable energy sources. The ambient temperature and irradiance substantially impact the energy produced by solar PV (SPV). The atmosphere rapidly modifies the temperature and irradiance. This article employs maximum power point tracking (MPPT) strategies to boost energy production. The MPPT controller is used to produce maximum power from the RES. The incremental conductance is combined with the emperor penguin optimization algorithm to utilize the greatest SPV power. The buck converter reduces the voltage using the extracted peak power of the SPV. To provide a reduced harmonic voltage waveform in the output, multi-level inverters are used. Increasing the level counter of a staircase waveform improves the output voltage quality. A 51-level inverter is utilized for this, which consists of many MOSFET switches to produce a 51-level output waveform. The 51-level inverter's current is controlled by the proportional resonance-based rain optimization algorithm (PR-ROA) controller, which also provides efficient switch tuning. In this situation, ROA adjusts the settings of PR and leads to reduced total harmonic distortion output signals. [ABSTRACT FROM AUTHOR]

In variable speed applications of high-power induction motors, current source inverters are usually used instead of voltage source inverters. Power switches delay and switching losses in high-power ranges, prevents inverters to operate properly in high frequencies. So the voltage and current waveforms of the motor supply consist of high harmonic content causing a high-torque ripple. One of the parameters that influences the torque ripple most is the stator flux reference value. Motors do not usually operate in their nominal load. Therefore, the optimum value of the flux is not equal to the nominal value. In this paper, an optimal i reference for vector control system of current source inverter fed induction motor is produced by applying a simple estimator. Simulation results show that torque ripple has been reduced, especially in the loads less than their nominal power, as significantly as power factor has been improved. Also flux reduction causes to noticeable reduction in core and switching losses. [ABSTRACT FROM AUTHOR]

This paper proposes two current-control strategies adopting the sliding-mode concept for single-phase current-source inverters (CSI) feeding a resistive load. The first strategy is based on forming a general sliding surface using the error variables of the inductor current and capacitor voltage. However, it is observed that with this type of control there exists a steady-state error in the capacitor voltage. Therefore, an integral sliding-mode-based current control using an additional integral term of the error variables in the sliding surface is proposed. It is observed that the additional integral term alleviates the steady-state error in the capacitor voltage. The existence conditions for stability are determined for both control strategies. It is shown that the compliance of the existence conditions for full operating range of the CSI can be assured if the complete ranges of operating conditions are taken into consideration. In order to reduce the switching losses and improve the quality of the output voltage, the three-level hysteresis function is implemented as two separate two-level functions for the switching devices. Computer simulations are performed to verify the theoretical results and for comparison with existing methods. Experimental results are also presented to support the theoretical considerations. [ABSTRACT FROM AUTHOR]

Currently, the use of Field Programmable Gate Array (FPGA) devices as control platforms is common in areas where real-time control is important, as renewable energy system. Grid-connected photovoltaic systems require control strategies to optimize the performance of the complete system. This article presents the implementation of a control strategy on a FPGA platform working with a single-phase grid-connected photovoltaic system developed in MATLAB/Simulink environment. The control strategy of the system consists of a variable-step MPPT algorithm with a predictive current control to operate a boost converter on the first stage. In the second stage, a simplified active and reactive power control ensures that the maximum power is transferred to the grid trough a cascaded H-bridge multilevel inverter. A single-phase PLL based on the PQ theory is used to track the frequency of the grid. The results obtained in the simulation allow to validate the proposed strategy. [ABSTRACT FROM AUTHOR]

In a distributed generation system, the nonlinear dynamics of a grid-interfaced inverter (GII) cause dynamic instability and power quality issues. Because traditional linear approaches rely on parametric fluctuations in controller parameters, adequate tuning is required. Some of the foregoing issues can be addressed using feedback and feedforward damping methods, but they require extra sensors and are ineffective in maintaining resilience against grid impedance variations and system parametric changes. Due to the digital control delay, they also add negative damping in a given frequency band, resulting in non-minimum phase behavior. The suggested control solution adds an observer-based adaptive control architecture to the existing inverter control. The concept of an energy function is used to depict grid dynamics at the GII terminals. On this dynamic energy signal, the nonlinear function will act to derive an ideal control parameter for the enhanced control algorithm. The proposed algorithm, which considers the system's nonlinearities, provides more robustness amid high- and medium-frequency grid dynamics, as demonstrated by simulation and experimental studies. [ABSTRACT FROM AUTHOR]

This study introduces a nine-level multilevel (MLI) inverter based on the switched-capacitor method. Not only does the suggested inverter ensure that the switches' maximum voltage stress is lower than the incoming voltage, but it also includes a voltage double boost capacity. As a result, it is indeed appropriate for high-voltage tasks. The suggested inverter has horizontal extension strategies that assist it to reach a higher level of output with voltage boost. This nine-level inverter could be made with two capacitors owing to a benefit of low voltage stress and devices with cheap power consumption. Furthermore, the self-balancing capability of capacitor voltage helps reduce control circuit complexity. The topology, working principles, modulation approach and the evaluation of the inverter's capacitor are presented. The proposed inverter's superiority is explored by comparing it to recently suggested hybrid and switched-capacitor multilevel inverters. Finally, a nine-level prototype is built to verify the theoretical analysis' accuracy as well as the suggested inverter's feasibility and efficiency. [ABSTRACT FROM AUTHOR]

In this study, a finite control set model predictive control strategy is proposed for a nine-switch converter system. The predictive control routine with discrete-solution space in energy transformation applications is widely used and offers a satisfactory closed-loop operation. However, the stability analysis of the predictive control method is a challenging task, and the practical stability approaches are applied to examine the closed-loop stability characteristics. Designing the guaranteed-stability predictive control is not an easy task since even the norm choice of the objective function may result in closed-loop instability. Regarding closed-loop stability, stability-guaranteed predictive sliding surface control approach is introduced in this study. The multi-objective cost function is reformulated in the proposed method as a sliding surface function usually used in sliding mode control methods. Thus, the best-suited control input that meets the sliding mode control stability criterion is picked. The proposed reformulation process enables the sliding surface function as an objective function, and the sliding surface function is gauged for each legitimate switching combination. The proposed control method is experimentally verified by using a 3.2 kW silicon carbide nine-switch inverter prototype. The experimental results prove that the proposed method guarantees closed-loop stability, and dual-AC load control is achieved. [ABSTRACT FROM AUTHOR]

The ant colony optimization (ACO) algorithm is generally used to create an optimal PI regulator added to the pulse width modulation (PWM) strategy for a five-level neutral-point-clamped (NPC) inverter implemented in electric vehicle (EV). As heavy transportation is our main focus, the proposed system was formed by two induction motors (IMs); each of which was fed by one NPC inverter. The two IMs were fixed to the front axle and the rear axle, respectively. The PDC-PWM (Phases Disposition Carrier-PWM) strategies for the three-phase five-level NPC inverter was employed in the rotor-flux-oriented control (FOC) of the induction motor (IM). Special interest was given to the analysis of the total harmonic distortion (THD%). Considering the dynamic loading conditions of an EV driven by an IM, the proposed ACO algorithm effectively calculated the required PI parameter to find the best PI regulator gains values. These optimizations were applied to the PDC-PWM strategy in order to obtain the minimum THD% in both current and voltage outputs. The effectiveness of the introduced system for a wide range of torque/speed variations was proven through simulation by developing a model of an IM traction inverter drive with the FOC strategy for closed-loop control. As the experimental test realization of the designed system was not possible because it is very expensive, the ACO optimization performance was confirmed by means of MATLAB/SimPower Systems simulations. [ABSTRACT FROM AUTHOR]

One of the most critical elements in the connection of photovoltaic (PV)-based systems used to generate electricity from solar energy is the inverter. The harmonic effects of the inverters to be connected to the grid should be as low as possible, and the total harmonic distortion (THD) should be less than 10%. A high THD value will distort the power quality on the grid side. For this reason, the THD value of the inverters in the grid connection approaches must be determined by spectral analysis to ensure that the necessary protection and improvements are made technically. In this study, a novel inverter topology, including six power switches and two power diodes, is presented, and the voltage data obtained from a grid-connected inverter are acquired in real time, and spectrum analysis is performed with the software developed with LabVIEW. The power efficiency of the proposed inverter is compared with conventional inverter types such as HERIC, H5, and H6 inverters. One of the novelty aspects of the proposed inverter topology is forming a proper freewheeling path including switches and diodes in the inverter branches that can provide a separate DC and ac components, and as a result, this prevents the following the PV side leakage currents to the ac grid side. In the spectrum analysis, the chirp Z-transformation (CZT) was used along the contours of the Z-transformation outside the unit circle. Using CZT, the z-transform was calculated for the inverter output voltage along the spiral lines in the z-plane. Besides, spectrum analysis was performed with fast Fourier transform (FFT) and compared with CZT. The results show that the CZT transformation is more efficient than the FFT algorithm and is useful in calculating a subset of FFT for a sequence. The performance of the proposed inverter is compared with conventional topologies. Hardware implementation and the output signals and the leakage current waveforms are also presented. [ABSTRACT FROM AUTHOR]

High component count and subsequent effects on volume and reliability have been the major concerns for practical applications of multilevel inverters (MIs). Recent emergence of the so-called reduced component count MIs (RCC-MIs) has been driven by the attempts to reduce the number of power switches for multilevel power conversion. In many of such topologies, the aspect of fault tolerance has not been given full consideration. In this work, some of the recently proposed RCC-MI topologies have been considered and analyzed in the light of imparting fault tolerance capability in the case of open-switch failure of any one of the power switches. In an RCC-MI, the occurrence of an open-circuit fault in a power switch would often lead to shut down due to the lack of redundant switching states. To overcome these occurrences, an optimal addition of power switches is described in this work so that the desired redundant states can be synthesized. The modified RCC-MI topologies so obtained have been analyzed under the normal and faulty conditions and computer simulations have been carried out using MATLAB/Simulink, and corresponding results have been presented. The results so obtained are experimentally validated to prove the feasibility of the proposed fault-tolerant topologies. [ABSTRACT FROM AUTHOR]

This manuscript discusses a novel harmonic current excitation technique for a wound rotor synchronous machine based on control of the time harmonic magneto-motive force (MMF) for brushless operation. Two inverters are used to feed the armature winding in such a way that at a time, one inverter supplies the current to armature winding. The two inverters are 180° phase-shifted. The inverter assignment is based on time-division multiplexing technique to generate continuous armature currents containing reasonable third-harmonic component beside fundamental component. This third-harmonic current component generates pulsating MMF and is induced in the rotor harmonic winding; the induced current is rectified and applied to rotor field winding to generate rotor field. The rotor field interacts with armature fundamental current component for torque generation. Finite element analysis is performed to verify the idea. [ABSTRACT FROM AUTHOR]

A speed-sensorless control strategy is investigated in a wide speed range based on extended Kalman filter (EKF) and direct torque control with space vector modulation (DTC-SVM) for three-level cascaded H-bridge inverter-fed permanent magnet synchronous motor drives. The implementation of conventional SVM technique to the multilevel inverters is considerably complicated and leads to high computational burden. A three-level SVM technique simplified on the basis of two-level voltage vector diagram is proposed to reduce this computational complexity, and in addition, to satisfy some requirements for the safe operation of the inverter such as smooth commutation and minimum number of switching. The estimations of rotor position and speed are achieved using an EKF without high-frequency signal injection, especially at very low and zero speeds. The load torque is also estimated simultaneously to account for the mechanical frictions at steady state to improve the estimation performance. Furthermore, the flux trajectory control based on maximum torque per ampere algorithm is implemented to ensure maximal efficiency for constant torque region. The feasibility and effectiveness of the proposed drive system is tested under different operating conditions and verified by the simulation results. [ABSTRACT FROM AUTHOR]