Current-fed quasi-Z-source inverter with coupled inductors

The quasi-Z-source inverters (qZSIs) were recently proposed as an important improvement to the traditional Z-source inverters (ZSIs). Besides the advantages inherited from the ZSIs, the qZSIs also have several of their own merits, such as reduced passive component ratings, continuous input current configuration, and so on. Unlike the traditional current source inverter (CSI) that can only boost voltage and allow unidirectional power flow, also differently from voltage-fed ZSI/qZSI that needs to replace the diode with a switch to achieve bidirectional power flow, the current-fed qZSI features voltage buck-boost and bidirectional power flow with an additional diode. There are three inductors in the current-fed qZSI, and the design of these three inductors is very important to the size, cost, and performance of the inverter. This paper presents a design of three-winding coupled inductors for the current-fed qZSI, which can effectively reduce the inverter size and weight. For the magnetic core and winding wire selection, the inductor currents and the current stress of the switches are analyzed in detail in both motoring operation and energy regeneration operation. A 5 kVA current-fed qZSI prototype, based on the novel reverse blocking IGBT (RB-IGBT) module, was developed in the laboratory. Experimental results are shown to verify the theoretical analysis.