Switched coupled-inductor Z-source inverters with large conversion ratio and soft-switching condition

This paper presents the concept of using a switched coupled-inductor cell for implementing quasi-Z-source inverters. By replacing one of original inductors found in the classical impedance network by a coupled-inductor, and adding one diode, new single-stage buck-boost inverter with a small count of elements and a high conversion ratio are obtained. The output voltage of the new inverter can be adjusted freely by varying the turn ratio of the coupled-inductor and the inverter shoot-through duration. The additional diode helps to circulate the leakage inductance energy to the load in a non-oscillatory manner. The transistors of the inverter turn on/off with soft-switching. The diodes turn on with zero-voltage switching and turn off with zero-current switching, their reverse-recovery problem is alleviated. The principle of the proposed converter, analysis of operation, and design guideline are included. Experimental results of the 1kW switched coupled-inductor quasi-Z-source inverter prototype are given for hardware verification. The theoretical analysis and simulation agrees well with experimental results.