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Non-isolated high-voltage gain soft-switching dc-dc converter is an ideal candidate for distributed generation system converters. This paper proposes a high-voltage gain soft switching quasi-Z-source dc-dc converter. The converter integrates a coupled inductor and switched capacitor into a quasi-Z-source network. Soft switching is achieved for all active devices in the converter by controlling the auxiliary switch Sa. By inheriting the advantages of the quasi-Z-source network and coupled-inductor/switched-capacitor, the converter has high voltage gain, high efficiency, low input current ripple, low voltage spike of main switch, and common ground. In addition, the efficiency of the converter is improved by recycling the energy of leakage inductance, resulting from an inherent active clamp of the main switch. The steady-state operation, voltage relationship, current/voltage stress, and power dissipation of each component of the converter have been analyzed and derived in detail. The properties of the proposed converter are verified by designing a 200 W prototype in the laboratory. When the input voltage is 48 V and the output voltage is 380 V, the converter efficiency reaches 96.92%, while the efficiency is 93% in a hard switching. The key waveforms of the converter obtained from the experiment agree well with the theoretical analysis results.

The Z-source inverter can overcome several inherent limitations of conventional inverters, realize buck–boost voltage capability with a single-stage inverter, and improve inverter's safety. However, it needs to be optimized in two aspects: mitigating the constraining effect of the shoot-through duty ratio D and the modulation index M ; reduction of the inductance of the magnetic elements and the size of the magnetic core in the Z-Source network. This article presents a new quasi-Z-source inverter (qZSI) that either has a coupled-inductor multiplier voltage rectifier (CMVR) cell or an improved CMVR cell embedded into it. The CMVR qZSIs can implement a boost factor given by $k_{N}/ (1-kD)$ , $k_{N}> 1$ , which mitigates the constraining effect of D and M , as well as enables high voltage boosting with a large value of M . The CMVR qZSI has low weight of the magnetic elements in the CMVR cell due to the use of step-down transformer. The operating principle, voltage relationship between each component, and the comparison in voltage and current stress on components, magnetic elements, has been described. A 1 kW prototype was built in the laboratory to verify the validity of the proposed inverter. Experimental results are in good agreement with the analysis results.

This article proposes a modified switched-coupled-inductor quasi-Z-source inverter, which is characterized by a continuous input current, low dc-link voltage overshoot, and high efficiency. The bootstrap capacitor in this improved module enhances the boost capability of the inverter at a low shoot-through duty cycle $D$ . Thanks to the distinct positions of the third and fourth windings $N_{23}$ and $N_{24}$ of the multiwinding coupled-inductor in the proposed inverter, these windings have low current stress during shoot-through state and no current flow at nonshoot-through state. The work environment of the coupled-inductor is optimized, and the inverter efficiency is substantially improved due to its low copper loss. This article studies the operating modes, analyzes the voltage and current stresses of different components, and studies their energy consumption in detail. Finally, the feasibility of the proposed inverter is validated via a 1-kW prototype developed in the laboratory and the test results are consistent with the theoretical analysis.

Z-source inverter (ZSI) can overcome some drawbacks of classical current- and voltage-source inverter, which have features such as high reliability and buck–boost capability of single-stage inverter. This article proposes an extensible ZSI architecture, abbreviated as EZSI. The proposed architecture provides high voltage gain at a small shoot-through duty ratio, which improves the output waveform quality. It inherits the advantages of continuous input current and low dc-link voltage overshoot of quasi-ZSI. The EZSI can be constructed with modularization, using low voltage components to construct a high-power single-stage inverter. A modular analysis method of EZSI is proposed, which divides the high-dimensional state equation of inverter into several independent low-dimensional state equations and simplifies the research of EZSI. A typical EZSI ( n = 2) L -mSSCL validates the correctness and feasibility of the proposed theory. Compared with the conventional high boost ZSIs, the proposed EZSI ( n = 2) L -mSSCL has advantages in the aspects of boost capacity, component stress, and inverter efficiency. The operating principle, characters design rules, and power dissipation of the components is analyzed in detail. A 1-kW prototype is used for experimental validation. The theoretical analysis results match with the experimental results.

An impedance-source inverter can offer the voltage buck-boost function in a single-stage circuit. Its advantages include a simple structure, safety, and reliability. This article proposes a Cockcroft–Walton multiplier voltage (CWMV) impedance-source inverter consisting of a modified CWMV circuit and an impedance-source inverter. There are two types of circuits: the CWMV Z-source inverter (ZSI) and the CWMV quasi-Z-source inverter (qZSI). In a CWMV qZSI, the input current is continuous, the voltage overshoot across the bridge is small, and the boost capability is great, with the disadvantage is that its passive component count is increased. This article studies the static and dynamic characteristics of the two inverters. The operating modes of the CWMV qZSI is studied, the voltage and current stress of each device are analyzed, the small signal model of the circuit is established, and a proportional-integral-differential controller with good control performance is designed. Compared with existing impedance-source inverters, a CWMV qZSI has obvious advantages in terms of the voltage and current stresses on components, and also in terms of its inductor size, magnetic core volume, and overall efficiency. The theoretical analysis was verified by a 1 kW laboratory prototype. The experimental results were consistent with the theoretical analysis.

This paper presents an improved Cockcroft- Walton Single stage high voltage gain inverter. The impedance network consists of a coupling inductor and an improved Cockcroft-Walton booster converter. A high quality output waveform is obtained with a smaller duty cycle and a larger modulation index. The proposed inverter reduces the ratio of turns of the coupling inductance, so it is lighter in weight and smaller in size. The 700W prototype designed by the laboratory tests the performance of the proposed circuit. Theoretical analysis, simulation and experimental results are completely consistent. The validity and practicability of the proposed converter are verified.

In this paper, a family of high efficiency high step-up dc-dc converter is presented, which inherits all advantages of both switched-inductor dc-dc converter and coupled-inductor dc-dc converter. The proposed converters can achieve high step-up capability with the proper duty cycle D (high or small D leads to the bad efficiency), obtain soft-switching conditions of active devices (including switch and rectifier diodes), and recycle the energy of leakage inductance to the output capacitor, which results in the high efficiency. The switch of converter operates in ZCS turn-on condition, which decreases the switching loss and improves the switch operating environment. The rectifier diodes cut off with ZCS condition, which improves the reverse recovery characteristics of diodes. The voltage relationships, operating principle, and operating modes are described in detail. Finally, experimental results verity the validity of the proposed switched-coupled inductor boost converter.

This paper presents an Integrated switched-coupled-inductor boost-flyback converter (abbreviated as SCIBFC), which has benefits of both Integrated boost-flyback converter (IBFC) and switched coupled-inductor boost converter. The principle of the proposed converter, analysis of operation (including the effects of parasitic parameters), and design guideline are included. SCIBFC achieves soft-switching conditions of active devices (ZCS turn-on in switch S and ZCS turn-off in the rectifier diode), which results in high efficiency and good EMI. Experimental results of the 20 W SCIBFC prototype is given for hardware verification. The theoretical analysis agrees very well with experimental results.