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In this article, we present a new type of Z-source inverter (ZSI) that replaces two inductors in the original quasi-ZSI with two transformers. It can produce a very high output voltage with the high value of the modulation index. Moreover, it enables both to provide a better power quality of output and to reduce the switching loss. In particular, the proposed quasi-clamped ZSI with two transformers give a unique solution to obtain high gain by reducing the turns ratio, rather than increasing it. Also, the leakage inductance of the transformer might cause huge voltage spikes across the inverter bridge. To deal with this problem, an effective clamping technique is proposed. As a result, this increases the overall efficiency of the system by utilizing the low-power switching devices. The characteristics of the proposed quasi-clamped ZSI with two transformers are comprehensively discussed with the detailed theoretical analysis. Thereafter, its performances are evaluated by both simulation and experimental tests. [ABSTRACT FROM AUTHOR]

This article proposes a novel sawtooth-carrier based pulsewidth-modulation (SCPWM) method for quasi-Z-source inverter (qZSI) with the zero-voltage-switching (ZVS) operation to reduce the total harmonic distortion (THD) and inductor current ripple. The conventional variable-duty pulsewidth-modulation (VDPWM) method has been being used for qZSIs because it causes the low switching loss. However, this method has the limitation not only to improve the THD of output current but also to reduce the size of inductor when it is applied to the qZSI. To figure it out, the proposed SCPWM method uses the sawtooth-carrier signal while keeping the benefit from the use of variable duty. In particular, the ZVS operation occurs whenever the edge of sawtooth-carrier signal is located in the time interval of shoot-through state. This allows to increase the carrier frequency of qZSI without any additional switching loss. Thus, both the THD of output current and the inductor current ripple can be reduced while keeping the high efficiency of system. The operating principle of the proposed SCPWM method is first explained in detail. Thereafter, its performance is mathematically analyzed and compared with that of conventional VDPWM method. Finally, its practical effectiveness is verified by the hardware experimental test. [ABSTRACT FROM AUTHOR]