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This paper presents the development of a Class-D full-bridge zero-voltage switching (ZVS) inverter, applicable to wireless power transfer (WPT) systems, operating at 13.56 MHz switching frequency with dynamic dead-time control (DDTC). Resonant-coupled WPT systems are being designed at ultrahigh switching frequencies to reduce the size of the wireless link and the passive components. Maintaining ZVS while controlling the output power delivered to a fixed or variable load is one of the major challenges of designing inverters at multi-MHz switching frequencies. DDTC is the approach deployed in this paper to sustain soft switching of a Class-D full-bridge inverter over the full range of output power while regulating the input dc bus voltage. Simulation results are presented to show that dynamically controlling the dead-time during input dc bus voltage variations reduces switch-node voltage overshoot, prevents large current spikes in the switching devices, and reduces associated high switching loss. Practical results obtained show that DDTC reduces switch-node voltage overshoot, increases the inverter efficiency, and reduces the steady-state temperature of the inverter during output power regulation. [ABSTRACT FROM AUTHOR]

In this paper, many impedance-source inverters with coupled inductors have been investigated to obtain a high step-up boost ratio. However, the leakage inductors in these topologies induce great voltage spikes at the dc link, which will increase the voltage stress of switches. Thus, the power level of inverters is limited. Furthermore, the efficiency of the inverters can be degraded by the losses associated with leakage inductors. To address abovementioned issues, this paper proposes a family of low-spike high-efficiency Y-source inverters. The proposed inverters have the ability of eliminating voltage spikes at the dc link and recycling the leakage energy via the additional diode and capacitor. In order to show the excellent characteristics of the proposed topologies, this paper compares the performances of the proposed inverters and the improved-Y-source inverter in many aspects. Simulation and experimental results have verified the abilities of the proposed inverters. [ABSTRACT FROM AUTHOR]

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 proposes an “isolated soft switching current fed LCC-T resonant dc–dc converter for PV/fuel cell applications.” This converter is able to achieve zero voltage switching for front-end inverter switches and zero-current switching for voltage doubler diodes. The majority of dc–dc converters have compact capacitive (C) filter in output, but high harmonic currents through transformer makes them bulky. The proposed converter attempts to improve harmonic content through a transformer under wide load and input variations as well as it can significantly reduce required turns ratio of transformer to achieve required output voltage. For the above reasons, the proposed converter can offer better footprints and therefore it can be a potential candidate for PV/fuel cell applications. This paper presents basic operating principal, detailed analysis, control, and design of the proposed converter with the help of an example. This converter operates in two modes, i.e., constant duty cycle mode and constant frequency mode, depending on load demand, and is explained through operating curves. Finally, experimental results are included for justifying the proposed theory. [ABSTRACT FROM AUTHOR]

This paper proposes a new dc–ac converter with a reduced number of semiconductor switches and gate drive and control circuit components. A salient feature of this inverter is its pure sinusoidal line-to-line voltages with no need for output filter. Also, the proposed inverter improves the voltage utilization factor of the input dc supply compared to the four-switch three-phase inverter (first best topology in the literature from the number of switches point of view) and standard six-switch inverter with sine pulsewidth modulation. The proposed inverter is capable of operating with a wide range of output voltages from zero to the full value of the dc input voltage by appropriately altering the instantaneous duty cycle. A three-phase universal inverter with only three power switch has been proposed in this paper for the first time ever, to our knowledge. For the purpose of providing a good compromise between fast transient response and stability, a model predictive controller is proposed. All the design expressions have been derived. A comparison with other dc–ac converters is given to show the merits of the proposed converter. Finally, satisfactory circuit operation is confirmed by experimental results from a laboratory prototype. [ABSTRACT FROM AUTHOR]

Soft-switching techniques of transformerless photovoltaic grid-connected inverters (TLIs) can significantly reduce switching losses, as well as soften switching processes. Conventional dc–ac soft-switching configurations proposed by Dr. Deepakraj M. Divan are invalid in TLIs because of the leakage current problem. In order to develop soft-switching techniques in TLIs, this paper proposes a new soft-switching configuration and a procedure to guide the invention of soft-switching TLIs. First, this paper proposes two basic resonance tanks related to dc bus polarities, and then, uses these basic tanks to elevate four popular full-bridge-type TLIs according to the proposed guideline. As a result, four soft-switching TLIs are gained. Second, this paper picks obtained soft-switching highly efficient and reliable inverter concept (HERIC) as example to analyze its soft-switching operation principle and performance. As a consequence, all active switches of the gained soft-switching HERIC circuit are switched under both of zero-current turn-on and turn-off conditions; the reverse recovery problem of freewheeling diodes is alleviated owing to the zero-current turn-off of diodes; meanwhile, the common-mode voltage at the switching frequency scale is still constant. Finally, some experimental results from a 3-kW universal prototype at 50-kHz switching frequency are provided to verify the effectiveness of the main contributions of this paper. [ABSTRACT FROM AUTHOR]

In this paper, two structures are proposed for the switched-inductor quasi-Z-source inverter. In the proposed structures to extend the voltage gain of inverter, two new switched-inductor structures are used. In the proposed structures, voltage across the capacitors in the Z-source network and in the switched-inductor is symmetric and small. The other advantage of proposed inverters is known as achieving higher voltage gain per smaller duty cycle ratio (of shoot-through). Compared with a conventional continuous input current switched-inductor quasi-Z-source inverter at the same gain voltage, there is less of a ripple of input current in the proposed inverters. In this paper, at first the both the conventional and the proposed switched-inductor Z-source inventers are thoroughly investigated to find out their governing relations. Then, the proposed Z-source inverters are compared with the conventional ones by simulating them to assess their performance efficiency. Next, applying the simple boost pulse width modulation the simulation is carried out with PSCAD/EMTDC software. After that, to evaluate the obtained results, the prototypes of the proposed inverters with 48 Vdc input voltage are used. [ABSTRACT FROM PUBLISHER]

Microinverters require high voltage gain capability for interfacing the low dc voltage output of photovoltaic (PV) module to single-phase ac grid. A two-stage nonisolated inverter is proposed in this paper, with a first boost stage and a second traditional pulse width modulated grid-tied inverter stage. The proposed boost stage consists of a coupled inductor added with a voltage multiplier to achieve the required high voltage gain at high efficiency and to operate over a wide input voltage range. Among the coupled inductor topologies, adding a clamp circuit is a common solution to limit the voltage spike caused by leakage inductance. In the proposed converter, the resonance between the coupled inductor and voltage multiplier is used to address the issue of voltage spike, thereby reducing both component count and device voltage stress. Detailed analysis and design procedure of the proposed converter is presented in this paper. Experimental results of a 250-W microinverter are presented to validate the proposed converter. [ABSTRACT FROM PUBLISHER]

In this paper, new half-bridge and full-bridge topologies for a switched-boost inverter are proposed. These topologies have a high boost factor in comparison with conventional types. In addition, the proposed topologies have continuous input current and can generate zero-voltage level in output. In this paper, the operation of the proposed inverters in different operating modes is analyzed. Then, the values of inductors and capacitors are designed. Moreover, the used switching pattern and its logical diagram are introduced. A comprehensive comparison between the proposed and conventional topologies in terms of the boost factor, the number of elements, and the efficiency shows the good features of the proposed inverters. Finally, to verify correct operation of the proposed topologies and derived equations, simulation and experimental results are presented. [ABSTRACT FROM AUTHOR]

A novel hybrid pulse width modulation (PWM) technique is proposed in this paper for two parallel interleaved, two-level, three-phase voltage source inverters (VSIs). The two parallel interleaved VSIs are analyzed as a three-level (3L) inverter. A 3L inverter provides minimum line current ripple when nearest three voltage vectors are applied. In this paper, a novel carrier-based PWM technique is developed that ensures the application of nearest voltage vectors, keeping average circulating current to zero over a switching period. For carrier-based implementation of the proposed PWM, generalized common-mode (CM) offsets are derived in terms of maximum and minimum values of reference signals. Each 3L space-vector sector is divided into seven subsectors. For each subsector, a CM offset is calculated, addition of which to reference signals ensures the minimum line current ripple and zero average circulating current. Simulation and experimental results are provided to validate the proposed technique. [ABSTRACT FROM PUBLISHER]

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]

In this paper, two topologies are presented for the enhanced-boost quasi-Z-source inverters (qZSI), namely continuous input current configuration and discontinuous input current configuration of enhanced-boost qZSI with two-switched impedance networks. Similar to enhanced-boost impedance-source inverters (ZSIs), these proposed inverter topologies possess very high boost voltage inversion at low shoot-through duty ratio and high modulation index to provide an improved quality output voltage. Compared to enhanced-boost ZSIs with two-switched Z-source impedance networks, these proposed inverter topologies share common ground with source and bridge inverter, overcome the starting inrush problem, and draw continuous input current and the lower voltage across the capacitors. Moreover, the input ripple current is negligible. This paper presents the operating principles and analysis of continuous input current configuration enhanced-boost qZSI with two-switched impedance networks and compares with ZSI, switched inductor ZSI, DA/CA-qZSI, and enhanced-boost ZSIs. The theoretical analysis is done and is validated through simulation and experimental results. [ABSTRACT FROM PUBLISHER]

A single-phase common-mode transformerless grid-connected photovoltaic (PV) converter, which is based on the integration of two stages, is proposed in this paper. Transformer elimination in grid-connected PV systems has many advantages. It not only reduces cost, size, and weight but also increases the complete system efficiency. Since there is no galvanic isolation between grid and PV array, a leakage current may appear due to the PV parasitic capacitance to the ground, if this is not taken into account in the converter design. This paper presents a dc/dc boost converter integrated with a full-bridge inverter. The integration of these two stages reduces the ground leakage current. The neutral line of the grid is directly connected to the negative terminal of the PV array, eliminating any possibility of leakage current in this terminal. The principle of operation of the transformerless converter is analyzed, and a 200-W topology is experimentally tested. [ABSTRACT FROM PUBLISHER]

This paper proposes the use of advanced bus clamping switching sequences to reduce the impedance network inductor current ripple of the three-phase Z-source inverter (ZSI). Proposed technique is named as ABC4_MCB. MCB denotes that the maximum constant boost control method is used for the voltage boosting. One of the conventional space vector pulsewidth modulation of ZSI, “ZSVM6,” is termed as ZSVM6_MCB under the maximum constant boost control method. The switching sequences of ABC4_MCB technique are designed in such a way that it offers around 34% reduction in the maximum instantaneous inductor current ripple as compared to the ZSVM6_MCB for the equal average switching frequency. The factor of percentage reduction in the inductor current ripple using the proposed technique is constant over the entire range of shoot through duty ratio (0–0.48). Theoretical findings have been verified using simulation and experimental results. [ABSTRACT FROM AUTHOR]

In recent years, a number of bidirectional inductive power transfer systems (BD-IPT) suitable for wireless grid integration of electric vehicles have been developed. These developments have been fueled by the enhanced efficiency and spatial tolerance offered by BD-IPT systems. A typical BD-IPT system utilizes two synchronized full-bridge converters operating at fixed duty cycles to drive the primary and secondary magnetic couplers. However, in order to cater for a wide range of loading conditions, additional circuitry is employed at the expense of cost and power density. As an alternative solution, this paper proposes a novel power converter, named a boost active bridge (BAB), to replace the full-bridge converters. The BAB topology caters to a wide range of loading conditions without the need for any extra switching devices. A comprehensive mathematical model that predicts steady-state currents, voltages, and power transfer is presented to highlight the operating principles of the BAB technology. Experimental results obtained from a 3.5-kW prototype show a nearly constant efficiency under all loading conditions, validating the viability of the proposed BAB topology. [ABSTRACT FROM AUTHOR]

Input-series-output-parallel (ISOP) inverter system is very suitable for high dc input voltage and large ac output current power conversion applications. If this topology is applied to the grid-connected occasion, a bulky-capacity grid-connected inverter can be built with multiple small-capacity standardized inverter modules, which can significantly improve the reliability of the system operation and facilitate system design. In this paper, we investigate an ISOP LCL-type grid-connected inverter system, and put forward an optimized way for the topology of combined LCL filters first. Then, the inverter-side inductor current is carefully chosen as the controlled variable and thus a concise distributed control method is proposed to achieve multiple control objectives. On the basis of the presented distributed control, the redundant control technique is also provided to heighten the reliability of the grid-tied ISOP inverter indeed. Finally, a three-module prototype is built and the experimental results validate the effectiveness of the raised strategy. [ABSTRACT FROM AUTHOR]

The magnetic resonant wireless power transfer (WPT) system with a class E inverter has wide application in mid-range power transmission, especially for several megahertz scenario. However, it is cumbersome for the existing modeling and analysis methods to obtain the analytical solution to the system variables, which limits the evaluation of system characteristic. This paper proposes a nonlinear mathematical model for the WPT system with a class E inverter. The equivalent small parameter method (ESPM) is first adopted to solve the proposed six-order nonlinear model, and symbolic-form steady-state periodic solutions are yielded. During the whole solving process, only three iteration steps are needed for the proposed method. Compared with other existing modeling and analysis methods, the symbolic periodic results acquired by the ESPM exhibit sufficient accuracy by virtue of the combination of more higher harmonics. Meanwhile, the calculation complexity is simplified remarkably. Simulation and available experiments validate the effectiveness and accuracy of the proposed method. [ABSTRACT FROM AUTHOR]

In this paper, a generalized switching modification method is proposed to reduce the root-mean-square (rms) current flowing into a dc-link capacitor in a dc–dc–ac structure consisting of a boost converter and a three-phase inverter. To analyze the current flowing into the capacitor, we analyze the currents at the respective converter and inverter sides. Based on this analysis, we derive an analytical method to find the modification time between the converter and inverter pulsewidth modulation (PWM) carriers through a Fourier series and approximation to facilitate real-time implementation. Real-time implementation of the modification time calculated by the derived method is described. To verify the validity of the proposed method, experimental results are presented based on a 1-kVA dc–dc–ac prototype. The proposed method has a better capacitor rms current reduction performance than the conventional method in various inverter power factors and PWM strategies. Especially, it has an excellent performance in mid-power factor level (0.95–0.1). [ABSTRACT FROM AUTHOR]

Synchronverters are inverters that mimic the behavior of synchronous generators. In this paper, we propose five modifications to the synchronverter algorithm from the paper “Synchronverters: Inverters that mimic synchronous generators,” (IEEE Trans. Ind. Electron., vol. 58, no. 4, pp. 1259–1267, Apr. 2011), to improve its stability and performance. These modifications are implemented in software and do not require any changes in the inverter hardware. The first two modifications concern the control of the virtual field current in the synchronverter so that it is more robust to faults. We prove the stability of the grid-connected synchronverter with this improved field current controller. The third modification is to increase the effective size of the filter inductors virtually. This is motivated using results from the stability analysis of a constant field current synchronous generator connected to an ac power grid and also by practical considerations. Simulations and experiments show that this leads to a much better response to changes in grid frequency, voltage, or to imbalance in the grid. The fourth modification is to change the formula for the (virtual) nominal active mechanical torque to take into account the (virtual) losses in the output impedance of the converter. This makes the tracking of the desired active power much more accurate. The fifth modification is to introduce virtual capacitors in series with the inverter outputs to filter spurious dc components from the current supplied to the grid. [ABSTRACT FROM PUBLISHER]

In this paper, a new topology for half-bridge Z-source inverter is proposed. The proposed topology has only one impedance network. Unlike to the conventional half-bridge inverter, the proposed topology can provide zero voltage level at the output. It also increases output voltage level and stabilizes it in the desired value. Capacitor voltage stress in the proposed topology is low, and, therefore, nominal voltage of capacitor and cost decreases. In this paper, the steady-state analysis of the proposed inverter in two new operations which are named synchronous operation of diodes and asynchronous operation of diodes is conducted based on mathematics calculations. A method to obtain high-voltage gains by cascading the Z-network and combining middle inductors is presented that leads to cost, size, and weight reduction. Comparison among the proposed converter with conventional ones shows its excellent performance. The experimental results have good agreement with analytical analysis for the proposed topology. [ABSTRACT FROM PUBLISHER]

A quasi-Z-source modular cascaded converter (qZS-MCC) is proposed for dc integration of high-power photovoltaic (PV) systems. The qZS-MCC comprises series-connected front-end isolated qZS half-bridge (HB) dc–dc converter submodules (SMs). With the front-end isolation, the qZS-MCC achieves high-voltage dc capability, while maintaining modularity and PV panel grounded. The post-stage qZS-HB handles the PV voltage and power flows, dc-link voltage balance, and output-series power integration. Whereas, the front-end isolation converters of all SMs perform a constant duty cycle, lowing the control complexity. There is no double-line-frequency power flowing through the dc-side PV panels, qZS inductors, and qZS capacitors in the qZS-MCC, so small qZS impedance is possible compared to the existing qZS cascaded multilevel inverter. The configuration, operating principle, power loss evaluation, and passive components design of the proposed system are investigated in this part of the paper. The system control, modeling, and corresponding verifications are stated in Part II of this paper. [ABSTRACT FROM PUBLISHER]

Due to the pulsating power at the inverter output terminals, the passive storage elements of the boost stage of the current-fed switched inverter (CFSI) contain a power frequency harmonic component (100 Hz), apart from dc and switching frequency components. In prior designs, the second harmonic component is suppressed by increasing the size of the input filter inductor and capacitor or by using additional circuits. This paper presents a complete characterization of a control-based approach to suppress the power frequency harmonic component in the input inductor current of a CFSI. It also presents a comprehensive characterization of the harmonic power redistribution. Using the proposed approach, it is demonstrated that the inductor value of a CFSI is reduced by 61% for the same peak-to-peak ripple. This leads to an improvement in the conversion ratio, efficiency, and power density of the overall converter. A SiC MOSFET-based CFSI with 75-kHz switching frequency is used to verify the proposed design philosophy. [ABSTRACT FROM AUTHOR]

Two parallel interleaved two-level (2L) three-phase voltage source inverters (VSIs) can be analyzed as a single three-level (3L) VSI. A generalized carrier-based method is proposed in this paper for implementing different 3L pulsewidth modulation (PWM) techniques using two parallel interleaved 2L VSIs. The proposed method modifies the given three-phase reference signals of 3L VSI for implementation of the PWM technique using two parallel interleaved 2L VSIs. The influence of nonidealities on the equivalent 3L PWM switching sequences is also discussed. To overcome the effect of nonidealities, a new modified discontinuous PWM technique (MDPWM1) is proposed. The analysis of different performance indices is carried out for different 3L PWM techniques, and the key advantages of different PWM techniques are identified. Simulation and experimental results are also presented. [ABSTRACT FROM AUTHOR]

The development of a photovoltaic ac module composed of a high static gain nonisolated dc–dc converter with current source output characteristic followed by an unfolding low-frequency inverter is presented in this paper. The operation of the dc–dc converter with high static gain and with reduced switch voltage is obtained using the Cuk converter integrated with the switched-inductor technique. The nonisolated structure allows the elimination of the volume and losses of the power transformer and leakage inductance, and an output filter configuration is proposed to reduce the high-frequency ground leakage current. The grid-tied inverter operating in a discontinuous conduction mode (DCM) allows a sinusoidal output current with low harmonic distortion (THD = 3.72%) to be obtained without current control loop and without the use of a current sensor at the output. The maximum power point tracking operation is obtained without the use of the current sensor. The DCM operation increases the current stress, but the proposed converter presents two switches and two input inductors sharing the input current in these components. The theoretical analysis, design procedure, and experimental results are presented for a prototype with a dc input voltage Vi = 30 V, an ac output voltage Vo = 127 V, and output power Po = 180 W. [ABSTRACT FROM AUTHOR]

Resonant converters with capacitive output filters are quite popular for their higher voltage gain and compact designs. But the majority of the converters underutilize the transformer as they are subjected to discontinuous currents. This discontinuous current possesses huge current ripples that produce huge core losses and aggravate the temperature rise of the transformer. This often leads to saturation of the transformer. This paper presents an LCC-T resonant dc–dc converter with a capacitive output filter operating all switches in the zero current switching (ZCS) switching mode and whose transformer current is a continuous sinusoidal with minimum stress on resonant tank components. This is achieved by bringing the transformer in series to a resonant inductor. The proposed converter is simulated in power simulation (PSIM) 11.0.1. A proof-of-concept model rated 288 W is designed and developed, and hardware results are presented as verification to theory. [ABSTRACT FROM AUTHOR]

This paper presents a complete design methodology of a Class-E inverter with a loosely coupled transformer under zero-voltage switching conditions. At a selected maximum coupling coefficient, the inverter satisfies both zero-voltage switching (ZVS) and zero-derivative switching (ZDS) conditions to achieve a high efficiency. As the coupling coefficient is decreased from its maximum value to zero, the inverter satisfies the ZVS condition over a wide range of load resistance. The proposed method absorbs the magnetizing inductance and the leakage inductance into the inverter topology. The closed-form expressions for all the Class-E inverter parameters are derived in terms of the coupling coefficient, including: 1) input impedance of the transformer with a complex load impedance; 2) equivalent phase of the resonant circuit for both nominal and suboptimum operations; and 3) slope of the switch voltage waveform. The relationship between the voltage slope and the coupling coefficient is introduced, which indicates the proximity of the operating point from ZVS and ZDS conditions. A design example of the Class-E inverter is presented to achieve both ZVS and ZDS, at an optimum coupling coefficient of 0.77, and ZVS condition for any coupling coefficient lower than 0.77 and over a wide range of load resistance. Saber simulations and experimental results are given to validate the soft-switching capabilities over a wide range of the coupling coefficient and load resistance. The theoretical results were in good agreement with Saber simulations and experiments. [ABSTRACT FROM AUTHOR]

In this paper, a novel integrated interleaved dual-mode time-sharing inverter (IIDMI) is proposed for grid-tied transformerless photovoltaic (PV) applications. While the dual-mode time-sharing conversion technique ensures minimum losses, the IIDMI also retains the advantages of interleaved topologies, such as low total harmonic distortion of the ac current with reduced filtering requirements, increased power density, and reduced current and thermal stresses of power devices. The leakage current problem, which is a main concern with the transformerless PV inverters, is solved by increasing the frequency of the main side band of the common-mode voltage above the resonance frequency of the common-mode impedance, while avoiding high switching losses. The current control, especially at transitions between the buck and the boost modes of operation, is highly improved by utilizing a fast-response deadbeat control scheme. The working principles of the IIDMI are explained in detail, and a 2.2-kW experimental prototype is implemented to confirm the theoretical achievements. [ABSTRACT FROM AUTHOR]

Usually, the parallel-compensated inductive power transfer (IPT) topology fed by a current-source inverter is controlled through variable switching frequency and fixed 50% duty cycle method. This enables the system to operate at resonance frequency, which drifts due to load and other parameter variations. Owing to this control constraint, the load requirements are fulfilled by adding extra dc–dc chopper at the output. This paper presents a new control technique for a parallel–series/series IPT network, fed from a full-bridge current-source inverter to meet the load demand directly by an inverter. Therefore, the extra chopper stage at the output side of the converter is eliminated. The control goals are achieved through a two-loop control method, where the inner input current loop controls the source current and the outer output current loop meets the load requirements. The detailed steady-state operation, converter design, small-signal modeling, and control are reported, and experimental results obtained from a 1.6-kW lab prototype are included to verify the mathematical analysis. [ABSTRACT FROM AUTHOR]

In this paper, a three-level quasi-switched boost T-type inverter (3L qSBT2I) is proposed. A new pulse-width modulated (PWM) control method is presented to reduce the inductor current ripple of the qSBT2 I. In the introduced PWM technique, the shoot-through duty cycle is maintained constant to keep the modulation index as high as possible. Then, the only control parameters of the qSBT2I are the duty cycles of the two additional switches. By controlling the duty cycles of the two additional switches, the voltage gain of the proposed qSBT2 I can be improved to a value larger than that of the conventional 3L impedance source inverters. The steady-state analysis, operating principles, and comparisons with the impedance source-based 3L inverters are presented. A 1-kW prototype is constructed to verify the operating principle of the 3L qSBT2I. An indirect dc-link voltage regulator and a capacitor voltage-balance controller are applied to the proposed qSBT2I. Simulation and experimental results are presented. [ABSTRACT FROM AUTHOR]

The success of electric vehicles (EVs) greatly depends on battery size, cost, lifetime, and capacity. The battery capacity of EVs has to contain enough energy to allow EV users to drive, at least, the minimum distance that internal combustion engine vehicles take. However, even with very efficient EVs and combining all the available highly efficient EV technologies, the battery capacity still needs to be large. Thus, one alternative to reduce the battery size is to improve the charging infrastructure by implementing sufficient public/private fast-charging locations, which will significantly increase the EV driving range with relatively low battery capacities. However, this kind of infrastructure requires charging with higher current capability, due to the high power levels involved in the fast-charging process. In this paper, a bidirectional dc/dc converter with six inverter legs connected to a three-phase output is proposed. The converter is similar to a three-phase dual-active-bridge (DAB) converter with more inverter legs in parallel. These additional inverter legs increase the converter current capability, without affecting the DAB main characteristics, preserving similar modulation techniques and DAB advantages. An accurate study about the proposed topology is carried out in this paper, and simulations and experimental results are shown for a 20-kW prototype, validating the theoretical analysis. [ABSTRACT FROM PUBLISHER]

This paper presents a transformerless inverter topology, which is capable of simultaneously solving leakage current and pulsating power issues in grid-connected photovoltaic (PV) systems. Without adding any additional components to the system, the leakage current caused by the PV-to-ground parasitic capacitance can be bypassed by introducing a common-mode (CM) conducting path to the inverter. The resulting ground leakage current is therefore well controlled to be below the regulation limit. Furthermore, the proposed inverter can also eliminate the well-known double-line-frequency pulsating power that is inherent in single-phase PV systems. By properly injecting CM voltages to the output filter capacitors, the pulsating power can be decoupled from the dc-link. Therefore, it is possible to use long-lifetime film capacitors instead of electrolytic capacitors to improve the reliability of the PV system. The mechanism of leakage current suppression and the closed-loop control of pulsating power decoupling are discussed in this paper in detail. A 500-W prototype was also built and tested in the laboratory, and both simulation and experimental results are finally presented to show the excellent performance of the proposed PV inverter. [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]

A merit of the interleaving reducing the switching harmonics allows for the reduction of the filter inductance. However, in the case of direct parallel voltage source inverters (VSIs), a severe circulating current occurs. To suppress the high frequency circulating current, coupled inductors (CIs) for the high impedance is inserted. However, the employed CIs induce a positive- or negative-sequence circulating current (i.e., a cross current) besides the zero-sequence circulating current already mentioned in the other papers. Due to different impedances developed by the current characteristics and the cross current in the CIs, VSIs becomes unstable when the resonant controllers are applied for the harmonic compensation such as 5, and 7th harmonics. In this paper, the cross currents and the impedances of CIs varying with the current characteristics are mathematically analyzed, and a novel current controller is proposed to solve this stability problem. The experimental results validate the proposed control scheme. [ABSTRACT FROM PUBLISHER]

A new single inductor dual buck full-bridge inverter is proposed in this paper. The inverter is improved on the basis of a dual buck inverter, and it retains the advantage of a no reverse recovery of body diode. The dc voltage utilization rate can be increased by adopting the voltage commutation bridge instead of the voltage-dividing capacitors in the inverter. In addition, comparing with other dual buck inverters, the inverter has just one filter inductor, which can make the volume and weight of the system decreased observably and improve the integration. The controlling method, combining the high- and low-frequency modulation, is adopted to weaken the complexity of control and improve the reliability and stability of the system. The operating principle, characteristic analysis, simulation and experiment are provided in this paper. A 1-kW prototype is established and tested, and the results of simulation and experiment verify the correctness of the theoretical analysis. [ABSTRACT FROM PUBLISHER]

An active method for double-frequency power ripple decoupling in single-phase inverters is presented in this paper, exhibiting the main advantage of not using additional power semiconductors besides the H-bridge. The proposed method requires only two capacitors placed between the midpoint and one end of each inverter leg. An original control solution of the inverter ensures the power ripple transfer toward the two decoupling capacitors without affecting the inverter output voltage. The simple design makes the proposed solution easy to adapt for single-phase inverters in H-bridge configuration. This paper focuses on the autonomous operation mode of the inverter, detailing its operating principle and the control analysis. The system performances, including the impact of the decoupling circuit on the inverter efficiency, are assessed by means of experimental results. [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]

The quasi- $Z$ source (qZS) cascaded multilevel inverter (CMI) (qZS-CMI) presents attractive advantages in application to photovoltaic (PV) power system. Each PV panel connects to an H-bridge qZS inverter (qZSI) to form a power generation module. The distributed maximum power point tracking and all modules' dc-link peak voltage balance can be achieved. However, it is the same with the conventional CMI that the second-harmonic ( $2\omega$) voltage and current ripples exist in each qZSI module. It is crucial for a qZS-CMI to design the reasonable qZS network parameters to limit the ripples within a desired range. This paper proposes an analytic model to accurately calculate the $2\omega$ voltage and current ripples of each qZSI module. A qZS impedance design method based on the built model is proposed to limit the $2\omega$ ripples of dc-link voltage and inductor current. Simulated and experimental results through using the designed 1.5-kW prototype validate the proposed analytic model and the design method. Furthermore, this paper analyzes all of the operating states for a qZSI module and calculates the power loss. The measured efficiency from the prototype verifies the theoretical calculation, and the qZS-CMI-based grid-tie PV power system is tested in practical. [ABSTRACT FROM PUBLISHER]

A single phase grid connected transformerless photovoltaic (PV) inverter, which can operate either in buck or in boost mode, and can extract maximum power simultaneously from two serially connected subarrays while each of the subarray is facing different environmental conditions, is presented in this paper. As the inverter can operate in buck as well as in boost mode, depending on the requirement, the constraint on the minimum number of serially connected solar PV modules that is required to form a subarray is greatly reduced. As a result, power yield from each of the subarray increases when they are exposed to different environmental conditions. The topological configuration of the inverter and its control strategy are designed so that the high-frequency components are not present in the common mode voltage, thereby restricting the magnitude of the leakage current associated with the PV arrays within the specified limit. Further, high operating efficiency is achieved throughout its operating range. A detailed analysis of the system leading to the development of its mathematical model is carried out. The viability of the scheme is confirmed by performing detailed simulation studies. A 1.5 kW laboratory prototype is developed, and detailed experimental studies are carried out to corroborate the validity of the scheme. [ABSTRACT FROM PUBLISHER]

This paper proposes the combination of a novel modified quasi-Z-source (MqZS) inverter with a single-phase symmetrical hybrid three-level inverter in order to boost the inverter three-level output voltage. The proposed single-phase MqZS hybrid three-level inverter provides a higher boost ability and reduces the number of inductors in the source impedance, compared with both the single-phase three-level neural-point clamped quasi-Z-source inverter and the single-phase quasi-Z-source cascaded multilevel inverter. Additionally, it can be extended to obtain the nine-level output voltage by cascading two three-level pulse width modulation switching cells with a separate MqZS and a dc source, which herein is called a single-phase MqZS cascaded hybrid five-level inverter (MqZS-CHI). A modified modulation technique based on an alternative phase opposition disposition scheme is suggested to effectively control the shoot-through state for boosting the dc-link voltage and balancing the two series capacitor voltages of the MqZS. The performances of both the proposed MqZS-CHI and the modulation techniques are verified through simulation and experimental results. [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]

In this paper, two switched-capacitor quasi-switched boost inverters (qSBIs) are proposed. By adding one capacitor and one diode to the qSBIs, the proposed inverters achieve high voltage gain with low voltage stress on active switches, capacitors, and diodes. The proposed inverters can extend to n-cell for voltage gain improvement. The operating principle, steady-state analysis, and impedance parameter selections of the proposed inverter are presented. A full comparison between the proposed inverter and other impedance-source inverters is addressed. A 500-W prototype is built to verify the operating theory of the proposed inverter in both the standalone mode and the grid-connected mode. Simulation and experimental results validate the theoretical analysis. [ABSTRACT FROM PUBLISHER]

Due to the global environmental issues and energy crisis, the injection of renewable energy sources (RESs) into the power system is continuously increasing. As the interface between RESs and power grid, grid-tied inverters using MOSFET switches, without traditional line frequency transformers, show some potential advantages, in terms of low cost, high efficiency, and lightweight and small size. Among several proposed configurations, the Aalborg inverter was proposed as a new family of high efficiency MOSFET-switch-based hybrid source inverters. For a conventional “half bridge” type Aalborg inverter, due to the imbalance of two independent dc sources, the input dc energies may not be fully utilized, which may reduce the efficiency of whole system. In order to extract the maximum energy from two independent dc sources, a coupled-inductor-based “half bridge” type Aalborg inverter is proposed in this paper. The principle of operation is presented and demonstrated through equivalent circuits. The effectiveness of a new energy balancing technique has been validated through simulations and experiments on a 110 V/ 500 W prototype. [ABSTRACT FROM PUBLISHER]

In this paper, dual-buck structured single-stage buck–boost inverters that use power MOSFETs to achieve high efficiency are presented. The proposed inverters require fewer switches, and half of the switches have reduced current stresses. They have no shoot-through problem; therefore, high system reliability can be obtained. The dead-time in PWM signals can be minimized or eliminated, which improving the quality of the output ac voltages and increasing the efficiency. In the proposed inverters, MOSFETs can be used without reverse-recovery issues of their body diodes to boost the efficiency and increase the switching frequency. To further improve the efficiency and stability of the proposed single-phase inverter, PWM strategies combining high- and low-frequency modulation are presented. A hardware prototype of the single-phase inverter was built and tested using resistive, inductive, and nonlinear loads. Experimental results for a 300-W prototype inverter show a 97.4% peak efficiency with a 25 kHz switching frequency. [ABSTRACT FROM AUTHOR]

In this paper, a framework for stability analyses of a typical inverter-based islanded microgrid with two types of nonlinear loads is presented, namely ideal constant power loads (CPLs), which are the loads supplied by tightly regulated power electronics converters, and dynamic CPLs, which are used to represent motor-drive systems with large time constants. The comprehensive dynamic model of the considered microgrid is first developed, based on which a bunch of small-signal models are deduced using Taylor expansion made at different stable operating points. Afterward, eigenvalue-theorem-based stability analysis and parametric sensitivity analysis are successively performed on the obtained small-signal models to verify the stability of the system, predict the system's unstable regions, and identify the effects of parameters on the stability boundaries. In the meantime, the impacts of different kinds of nonlinear loads on the system stability are studied. Hardware-in-the-loop (HIL) real-time simulation platform of a 30-kVA microgrid, which is mainly formed by a 10-kVA photovoltaic (PV) system, a 10-kVA wind energy conversion system, a 10-kVA lithium-ion battery energy storage system, and two CPLs, is established in Typhoon HIL 602 device. The validity of the theoretical results is verified by real-time simulation results. [ABSTRACT FROM AUTHOR]

The parallel three-phase grid-connected converters sharing dc and ac bus can increase the system power level effectively. However, the zero sequence circulating current (ZSCC) will occur inevitably under space vector pulse width modulation or discontinuous pulse width modulation (DPWM). In this paper, the mechanism and the mathematical model of ZSCC are studied. Then, a hybrid PWM (HPWM) strategy is proposed to suppress the ZSCC based on the same zero sequence voltage injected, which is dependent on the common grid information. The dc voltage utilization of HPWM can be extended compared with sinusoidal PWM (SPWM). The number of parallel modules can be infinity theoretically by using HPWM. It is noted that there is no internal commutation among modules (expect the dq current reference). Finally, the feasibility and the effectiveness of the proposed method are verified by experiments. [ABSTRACT FROM AUTHOR]

The battery energy-stored quasi-Z-source (BES-qZS)-based photovoltaic (PV) power generation system combines advantages of the qZS inverter and the battery energy storage system. However, the second-harmonic ( \text2\omega ) power ripple degrades the system's performance and affects the system's design. An accurate model to analyze the \text2\omega ripple is very important. The existing models did not consider the battery, or assumed a symmetric qZS network with $L_{{1}}= L_{{2}}$ and $C_{{1}}= C_{{2}}$, which limits the design freedom and causes oversized impedance parameters. This paper proposes a comprehensive model for the single-phase BES-qZS-PV inverter system, where the battery is considered and there is no restriction of $L_{{1}}= L_{{2}}$ and $C_{{1}}= C_{{2}}$ . Based on the built model, a BES-qZS impedance design method is proposed to mitigate the \text2\omega ripple with asymmetric qZS network. Simulation and experimental results verify the proposed \text2\omega ripple model and impedance design method. [ABSTRACT FROM AUTHOR]

This paper highlights the limitations of the dynamic response of a grid-tied inverter connected through an inductor $L$ when it is controlled using a proportional+resonant controller. Then, a new resonant current controller structure is proposed. This structure can be used to control the current injected by a grid-tied inverter through an $L$ filter. When compared to the classic design, the proposed controller has better transient response, both to current reference and grid voltage changes. This is verified through simulation and experimental results. [ABSTRACT FROM AUTHOR]

Microinverters for photovoltaic (PV) modules can improve the energy generation by reducing the effects of shading, since the energy harvesting of each PV module can be controlled individually. In this context, this paper presents a topology of single-stage transformerless grid-connected boost microinverter. It promotes high voltage gain without using a preregulator circuit or a high/low-frequency transformer. A 500 W laboratory prototype was implemented and experimental tests were carried out so that the proposed microinverter was evaluated in a grid-connected PV system. Experimental analysis was performed in order to corroborate the theoretical approach and to verify the effectiveness of the proposed modified Perturb and Observe “Gama” maximum power point tracking technique and the proportional-resonant (P-Res) grid current controller under different irradiation conditions and under partial shading. [ABSTRACT FROM PUBLISHER]

This paper presents the design, analytical estimation of power losses, and experimental measurement of choke inductors for switched-mode power inverters. The described approach is applicable to a wide variety of circuits such as Class-E inverters and converters. The expressions required to design the magnetic core in the choke inductor using the area–product ($A_p$) method are given. The equations for the dc resistance, ac resistance at high frequencies, and dc and ac power losses are provided for the solid round winding wire. To validate the presented approach, an example class-E zero-voltage switching power inverter with practical specifications is considered. A core with air gap is selected to avoid core saturation in the choke inductor, which conducts dc current and a small ac current. The gapped core power loss density and power loss are estimated using Steinmetz empirical equation. It is shown that the winding power loss due to the dc current is dominant for the given design. A comparison between the area–product $A_p$ method and the preexisting core geometry coefficient $K_g$ method is presented. The measured magnitude of the inductor impedance has shown that the designed choke is useful up to ten times the switching frequency. [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]