I. Introduction
The quasi-Z-source inverter (qZSI) has attracted much attention in renewable energy applications like photovoltaic [1], [2], wind turbine [3], [4], and fuel cell systems [5], [6]. As a substitute to the conventional two-stage inverter, the qZSI increases the system efficiency and reliability by adopting the shoot-through (ST) state, which makes the qZSI operate as a single-stage converter [7]. Fig. 1 shows the typical configuration of a three-phase qZSI, which contains a quasi-Z-source network (qZSn), a three-phase inverter, an filter, and a resistive load. Although the input current is continuous when compared with the Z-source inverter, the inductor current ripple of the qZSn is not optimal in most applications. Large inductor current ripples will result in higher inductor and switching losses, which further leads to distortions in the output current [8]. Increasing the switching frequency can reduce the inductor current ripple to some extent, but the increased switching losses will in turn reduce the system efficiency [9]. Larger inductance can also contribute to smaller inductor current ripples, but the volume of the inductors will also increase, lowering the power density of the entire system [10]. Meanwhile, dedicated pulsewidth modulation (PWM) techniques were developed to reduce the inductor current ripple in impedance source converters.