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In this paper, a new family of impedance source inverters is presented. It employs high-frequency electrical isolation between the inverter bridge switches and the load along with voltage clamping across the dc-link voltage. Conventional Z-source inverters (ZSIs) employs an impedance network that consists of inductors and capacitors. It has unique features that realize both step-up/step-down functions and eliminates the need of dead/overlap times. This paper extends this novel concept by using electrical isolation in impedance source inverters. High-frequency isolation has many advantages in terms of immunity and reliability; when applied with impedance source inverters this makes ZSIs a preferable choice for industrial applications. In photo-voltaic systems, the addition of the high-frequency transformer provides safety by avoiding the injection of dc circulating current into the grid, without the need of an external bulky line frequency transformer. The gain of the proposed inverter design can be accurately selected by choosing the turns ratio of the high frequency transformer (HFT) or by adjusting the shoot-through duty cycle (STDC) to the inverter. This allows for greater freedom especially when utilizing a higher modulation index, with the STDC allowing dynamic gain adjusts to be done speedily during operation of the inverter. Additionally, a dc-rail voltage clamping technique for the proposed class of isolated ZSIs is also discussed. This technique provides benefits not only in improving the output voltage quality, but also in reducing voltage stress of the active and passive components by minimizing the voltage spikes across the switching devices. In this paper, several high-frequency isolated ZSIs are presented, and an example isolated improved ΓZSI design is shown and discussed in detail. Simulations are provided for the proposed class of isolated inverters to verify their working. Further experimental investigation has been done for which results for the isolated improved ΓZSI are reported. These empirical results have largely confirmed the expected benefits that were determined through simulation and accurate model-based testing. [ABSTRACT FROM AUTHOR]

This paper investigates and evaluates the performance of a single-phase split-source inverter (SSI), where an alternative unidirectional dc–ac configuration is used. Such configuration is utilized in order to use two common-cathode diodes in a single device instead of using two separate diodes, resulting in minimum parasitic inductance in the commutation paths. In this paper, the analysis and modulation of the single-phase SSI using this alternative configuration is discussed, and the analysis of the low-frequency component in the dc side is introduced. Moreover, the features behind employing the triangular, the trailing-edge sawtooth, and the leading-edge sawtooth carriers with the single-phase SSI are discussed, and the differences among these carriers are highlighted. In order to highlight the performance of the proposed SSI, a comparative study is conducted with the two-stage architecture and the single-phase quasi-Z-source inverter (qZSI). The introduced analysis is enhanced with simulation results using MATLAB/PLECS models, where a 1-kVA single-phase SSI is designed and simulated. Finally, the designed 1-kVA single-phase SSI is implemented experimentally and tested at different operating points, i.e., at different voltage gains, and a maximum efficiency of $95.5\%$ is obtained. [ABSTRACT FROM PUBLISHER]

Induction heating technology is leading technical advances in home appliances due to the benefits inherent to the contactless energy transfer including high efficiency, fast heating, safety, cleanness, and accurate control, among others. Recent design trends are focused on developing more versatile cooking appliances for an improved user performance. To achieve such implementations, new multicoil architectures and power converters must be developed. This paper proposes the series-resonant multiinverter as an efficient, versatile, and cost-effective alternative to supply multiinductor systems. One of the main design challenges is the high blocking voltage of power devices, which may compromise the converter performance. This paper proposes an optimized modulation strategy to reduce the maximum device voltage, enabling an optimized converter design with improved reliability and performance. The proposed modulation is analytically studied and tested using a multicoil induction heating converter prototype, proving the feasibility of this proposal. [ABSTRACT FROM PUBLISHER]

Connecting legs in parallel in a voltage source inverter is a way to increase the output current and, thus, its rated power. The connection can be made using either coupled or uncoupled inductors, and achieving an even contribution to the output current from all the legs is a crucial issue. Circulating currents produce additional losses and stress to the power devices of the converter. Therefore, they should be controlled and minimized. An efficient technique to attain such balance when coupled inductors are used is presented in this paper. The proposed technique can also be used when the inductors are uncoupled, since it is a particular case where the coupling coefficients are zero. This technique does not include proportional–integral controllers and does not require any parameter tuning either. The exact control action needed to reach current balance is straightforwardly calculated and applied. Experimental results are shown in this paper to verify the efficiency of the proposed balancing method. [ABSTRACT FROM PUBLISHER]

A new space vector modulation, i.e., ZSVM3, for three-phase quasi-Z-source rectifier (qZSR) is proposed. All switches in the three-phase bridge can be turned on and turned off with zero current or zero voltage using the proposed ZSVM3 with no auxiliary circuit. The current through the inductors of the quasi-Z-source network operates in a boundary conduction mode or discontinuous conduction mode to achieve all freewheeling diodes turned off with zero-current switching (ZCS). At the same time, the switch in the quasi-Z-source network can be turned on with ZCS. Besides, the voltage stress of all switches is equal to dc-link voltage. The operation principle of the qZSR is analyzed in detail, and the calculated value of the quasi-Z-source inductor is given. The proposed theory in this paper is verified by a 2-kW prototype. [ABSTRACT FROM PUBLISHER]

Multilevel current-source inverters have proved to be a high-performance option for industrial applications due to reliability, fault-tolerant capabilities, quasi soft switching, and the use of lower filter capacitor values. One of its major challenges is to balance the internal currents that feed each module. Imbalances could be caused by manufacturing deviations of the reactive components, temperature drift or aging, nonlinear loads, and modulation errors, among others. Using the well-known phase-shift carrier sinusoidal pulse width modulation, a slight change in the amplitude of the carrier signals produces a variation in the average value of the internal currents. In this paper, we introduce a control strategy to balance the current of the inductors and its implementation in a prototype. Simulation and experimental results at different operating conditions show a robust behavior of the control system along with a low distortion in the output voltages and currents of the converter. [ABSTRACT FROM PUBLISHER]

Due to a substantial shortage of conventional energy sources, the utilization of renewable energy is gaining attention. Power converters form interfaces to provide power from renewable energy sources to end user systems. Impedance-source inverters (ZSIs) have become a research hotspot and are widely used to overcome the drawbacks of conventional voltage-source inverters and current-source inverters such as two-stage power conversion and less immunity to electromagnetic interference noises. This paper presents various transformer-based ZSIs mainly classified as trans-ZSIs, improved trans-ZSIs, inductor-capacitor-capacitor transformer ZSI, TZSIs, and their comparisons with a new family of ZSIs called Γ-Z-source inverters (ΓZSI). Full operational analysis of an improved ΓZSI with the clamping diode D2 and its benefits over the conventional ΓZSI are also discussed. The improved ΓZSI utilizes a higher modulation index and consequently a lower duty cycle to achieve same gain, thus reducing the switch voltage stress and providing better output quality. Additionally, an extra diode provides voltage clamping to the dc-link voltage to limit voltage overshoots. The comparative evaluations of all the above mentioned ZSIs are presented in the literature and to validate the advantages of the improved ΓZSI, simulations, and experimental comparisons are also performed. [ABSTRACT FROM AUTHOR]

Impedance-source inverters are inverters with voltage-buck–boost capability that cannot be achieved by the traditional inverters. Their boost capability is introduced by shorting their phase legs without causing damages. Impedance-source inverters are therefore less prone to false triggering caused by electromagnetic interference. Present impedance-source inverters are, however, burdened by their low modulation ratio at high input-to-output gain. Such low modulation usually leads to high-voltage stresses across the components and poor spectral performance at the inverter output. To avoid these problems, inverters with coupled transformers have been introduced, but they usually lead to high turns ratio, and hence many winding turns, at high gain. An alternative would then be the asymmetrical \Gamma-source inverters proposed in this paper, whose gain is raised by lowering their turns ratio toward unity. The input current drawn by the proposed inverters is smoother and, hence, more adaptable by the source. Theories and experimental results have been presented in this paper for validating the concepts proposed. [ABSTRACT FROM AUTHOR]

The five-phase coupled-inductor inverter is a newly proposed option for three-level five-phase inverter drives. This paper comprehensively analyzes the inverter including the coupled-inductor current, current stress on the dc-link capacitors, and a comparison of these performance aspects using three pulse width modulation (PWM) strategies. Mathematical derivations of the inverter currents and the associated current stress reveal that the current stress is not only influenced by the choice of modulation strategy, as in the neutral-point-clamped topology, but also by the value of coupled inductance; furthermore, the choice of the modulation strategy impacts the core loss of the coupled inductors. Three carrier-based PWM methods are considered: sinusoidal PWM (SPWM), and two methods with the common-mode voltage reduction (referred to as CMVR1 and CMVR2) for the five-phase coupled-inductor inverter. CMVR2 is shown to be the best solution if common-mode voltage reduction is required. The analysis demonstrates that SPWM performs better with respect to current stress and inverter losses, therefore is the preferable modulating strategy for the five-phase coupled-inductor inverter if common-mode voltage reduction is not required. The analysis is verified by simulations and experiments. [ABSTRACT FROM AUTHOR]

This paper describes the design procedure and performance of an LCL grid filter for a medium-voltage neutral-point clamped converter to be adopted for a multimegawatt (multi-MW) wind turbine. The unique filter design challenges in this application are driven by a combination of the medium-voltage converter, a limited allowable switching frequency, component physical size and weight concerns, and the stringent limits for allowable injected current harmonics. Traditional design procedures of grid filters for lower power and higher switching frequency converters are not valid for a multi-MW filter connecting a medium-voltage converter switching at low frequency to the electric grid. This paper demonstrates a frequency-domain-model-based approach to determine the optimum filter parameters that provide the necessary performance under all operating conditions given the necessary design constraints. To achieve this goal, new concepts, such as virtual-harmonic content and virtual filter losses are introduced. Moreover, a new passive-damping technique that provides the necessary damping with low losses and very little degradation of the high-frequency attenuation is proposed. [ABSTRACT FROM AUTHOR]

This paper proposes a new topology for an enhanced-boost Z-source inverter (ZSI) with combined two Z-impedance networks. By two Z-impedance networks and low shoot-through duty cycle, the proposed inverter produces high output voltage gain. In traditional ZSIs for high boosting voltage, a low modulation index is required; hence, under these conditions, the output voltage will have low quality with high total harmonic distortion. Compared with the conventional high-boost ZSI topologies, the proposed inverter uses shorter shoot-through duration and a larger modulation index to improve the output waveform quality. Comparison between the proposed topology and previously proposed schemes, in terms of inductor numbers, voltage and current stresses on elements, sizes of inductors and capacitors, efficiency, and switching device product (SDP) factors of diodes, is made, and the results verify the priority of the proposed topology. The operating principle of the proposed topology is analyzed in detail. Both simulation and experimental results verify the high performance of the proposed inverter. [ABSTRACT FROM PUBLISHER]

Back-to-back converters have been typically used to interconnect microgrids. For a back-to-back current-source converter, the dc-link current ripple is one of the important parameters. A large ripple will cause electromagnetic interference, undesirable high-frequency losses, and system instability. Conventionally, with a given switching frequency and rated voltage, the current ripple can be reduced by increasing the dc-link inductor, but it leads to bulky size, high cost, and slow dynamic response. To solve this problem, this paper reveals that the current ripple can be significantly reduced by adjusting the gate patterns of space vector modulation between the rectifier and the inverter in a back-to-back converter. The experimental results verify the effectiveness of the proposed method. [ABSTRACT FROM PUBLISHER]

Renewable energy sources can be used for electric power generation to supply specific devices in distributed systems such as smart grids. Hydrogen fuel cells have proven to be an effective solution to produce electrical energy with fairly good efficiency and minimum environmental pollution. A single-stage solution to interconnect a fuel cell with a low-voltage distribution system is proposed in this paper. The traditional boost dc/dc converter plus voltage source inverter is replaced by a single-stage multilevel current-source inverter (MCSI). The MCSI can both interconnect to the grid and perform the maximum power point tracking algorithm. This novel single-stage converter approach provides active power to the grid, power factor compensation, and reduction of the line current harmonic content. The synchronization, modulation, and control scheme are implemented on a field-programmable gate array board using a fast-prototype high-level synthesis tool to reduce design time. Both simulation and experimental results show excellent behavior and fast dynamics while complying with IEEE and IEC harmonic content regulations. [ABSTRACT FROM PUBLISHER]

This paper presents a novel combined-synchronous-rectifier high-frequency-link (CSR-HFL) inverter. Three types of conventional HFL inverters are analyzed and their performance is summarized. According to one of the conventional HFL inverters, i.e., cycloconverter-type HFL (CHFL) inverter, a combined rectifier topology is deduced. To prevent a shorted circuit, two additional switches are used in the new topology. The operation mode of the CSR-HFL inverter is analyzed and the mathematical relationships are given. The difference and correlation, and advantages and disadvantages, are analyzed between the CSR-HFL inverter and the conventional HFL inverter. The relevant grid-connected inverter, ac/ac converter, and full-wave CSR-HFL inverter are also given. The experimental results verify that the proposed CSR-HFL inverter has excellent performance and high efficiency. [ABSTRACT FROM PUBLISHER]

The quasi-Z-source cascaded multilevel inverter (qZS-CMI) presented many advantages over conventional CMI when applied in photovoltaic (PV) power systems. For example, qZS-CMI provides the balanced dc-link voltage and voltage boost ability, saves one-third modules, etc. However, current research studies only disclosed control of single-phase qZS-CMI-based PV power systems, and there was no literature related to control of three-phase qZS-CMI-based PV power systems. In this paper, for the first time, three-phase qZS-CMI's control is proposed and demonstrated for application to PV power systems. The models of PV-panel-fed qZS H-bridge module and qZS-CMI-based PV power system are built to accurately design control algorithms for each module and the whole system. The proposed control method includes the distributed maximum power point tracking for each module, dc-link peak voltage balance control for all modules, and grid-tie control for the whole system; moreover, a new multilevel space vector modulation method is proposed for the three-phase qZS-CMI. Simulation and experimental results on a test bench with a three-phase seven-level qZS-CMI-based PV power system verify the proposed control and modulation methods. [ABSTRACT FROM PUBLISHER]

This paper proposes an active front-end solution to balance the dc-link capacitor voltage of the five-level diode-clamped inverter. Capacitor voltage balancing is performed by a three-level boost converter connected to the two inner capacitors of a five-level diode-clamped inverter and additional balancing circuits at the other two outer capacitors. The proposed configuration is tested through simulation and experiment for various load power factor conditions at a high modulation index. The result demonstrates the reliability of the proposed configuration to balance the dc-link capacitor voltage at the desired level. [ABSTRACT FROM PUBLISHER]

The voltage range of a renewable energy source, such as the photovoltaic cell, is influenced by the environment, light, temperature, and so on. The power conditioning system should adapt to the wide input voltage and have buck–boost ability. Based on the structure of the “ac/ac unit,” this paper presents a novel active buck–boost inverter (ABI) topology suitable for wide-range input, which can realize buck–boost conversion in a quasi-single-stage inverter. The ac/ac unit composed of active switches is utilized to perform voltage boost without introducing additional passive elements, which is in favor to the system power density and efficiency. Operational analysis in buck and boost modes are presented, and the modulation strategy applied in the ABI is also developed. Simulation and experimental results are presented to verify the operational principle and its modulation strategy. [ABSTRACT FROM PUBLISHER]

High-boost dc-ac inverters are used in solar photovoltaic (PV), fuel cell, wind energy, and uninterruptible power supply systems. High step-up and step-down capabilities and shoot-through immunity are some of the desired properties of an inverter for a reliable, versatile, and low-distortion ac inversion. The recently developed Z-source inverter (ZSI) possesses these qualities. However, the realization of ZSI comes at a cost of higher passive component count as it needs two sets of passive filters. A switched boost inverter (SBI) has similar properties as ZSI, and it has one L\-C pair less compared to ZSI, but its gain is less than ZSI. This paper proposes the current-fed switched inverter (CFSI) which combines the high-gain property of ZSI and low passive component count of SBI. The proposed inverter uses only one L\-C filter and three switches apart from the inverter structure. The inverter topology is based on current-fed dc/dc topology. Steady-state analysis of the inverter is presented to establish the relation between the dc input and the ac output. A pulse width modulation (PWM) control strategy is devised for the proposed inverter. An experimental prototype is built to validate the proposed inverter circuit in both buck and boost modes of operation. A 353-V dc-link and a 127 V (rms) ac are obtained from a 35.3-V dc input to demonstrate the boost mode of operation. A 200-V dc-link and a 10.5-V (rms) ac are obtained from a 37.8-V dc input to verify the buck mode of operation of CFSI. [ABSTRACT FROM PUBLISHER]

This paper presents a novel direct current-fed interleaved phase-modulated single-phase unfolding inverter for fuel-cell applications. Two active-clamped zero-voltage switching current-fed half-bridge isolated converters are interleaved in parallel input and series output configuration. Phase modulation is proposed to control these two converter cells, which generate a rectified sinusoidal pattern at the dc link. A simple H-bridge unfolding dc–ac inversion is used to produce single-phase sine voltage at line frequency switching using square-wave control. This not only simplifies the inversion stage in terms of modulation but also reduces the switching losses. Direct front-end current-fed based unfolding inverter is not reported in literature yet. Detailed analysis and design of the proposed direct current-fed single-phase unfolding inverter has been presented. Simulation waveforms using PSIM 9.0.4 are given to verify the presented analysis and design. Experimental results on a laboratory prototype rated at 200 W are demonstrated to support the investigation, to validate the accuracy of the proposed analysis and design, and to test the performance. [ABSTRACT FROM PUBLISHER]

In this paper, a kind of zero-crossing distortion (ZCD) generated in the grid-connected current of a single-phase grid-connected inverter with unipolar hysteresis current control is investigated. By establishing the mathematical model of the grid-connected inverter around the zero-crossing points (ZCPs), the reason for causing the current ZCD is presented. It is ascribed to the slope of the actual current less than that of the reference one around the ZCPs. The expressions of the critical phase angle (the starting point of the current ZCD) and the amplitude of the current distortion corresponding to the parameters of the inverter and connected utility grid are obtained, and the solution for the ZCD based on on-line leading phase angle compensation is proposed. Simulation and experimental results verify the accuracy and feasibility of the theoretical analysis and the proposed solution. [ABSTRACT FROM PUBLISHER]

The main contribution of this paper is the derivation rules summarized from existing high-performance inverters with H6-type configuration, which makes novel topologies possible. In addition, a novel high-efficiency single-phase transformerless photovoltaic inverter with hybrid modulation method is also proposed and evaluated as an example. Without input split capacitors, common-mode voltage and leakage current issues in a nonisolated system with H6-type configuration are eliminated, and the feature of a three-level output voltage in the inverter bridge's middle point helps inductors and power quality optimization. The detailed operation principles with hybrid modulation strategy combined with unipolar and bipolar pulsewidth modulation schemes are presented. Experimental results of a 2200VA prototype verify the proposed topology with hybrid modulation method. [ABSTRACT FROM PUBLISHER]

In this paper, a multilevel current-source inverter (MCSI) topology is analyzed. The issue of constructing a novel modular single-rating inductor MCSI is explored, taking advantage of the features of field-programmable gate arrays (FPGA) for control and gate signal generation. The proposed topology is built with identical modules where all inductors carry the same amount of current, simplifying the construction and operation of industrial applications with higher efficiency. A new state-machine approach, which is easy to implement in an FPGA, and a proper implementation of the phase-shifted carrier sinusoidal pulse width modulation (PSC-SPWM) allow both current balance in all modules and effective switching-frequency minimization. The performance of the MSCI proposed is simulated with Matlab and is verified by constructing a prototype. [ABSTRACT FROM PUBLISHER]

A novel switched-capacitor inverter is proposed. The proposed inverter outputs larger voltage than the input voltage by switching the capacitors in series and in parallel. The maximum output voltage is determined by the number of the capacitors. The proposed inverter, which does not need any inductors, can be smaller than a conventional two-stage unit which consists of a boost converter and an inverter bridge. Its output harmonics are reduced compared to a conventional voltage source single phase full bridge inverter. In this paper, the circuit configuration, the theoretical operation, the simulation results with MATLAB/SIMULINK, and the experimental results are shown. The experimental results accorded with the theoretical calculation and the simulation results. [ABSTRACT FROM PUBLISHER]