Inductor Current Ripple Analysis and Reduction for Quasi-Z-Source Inverters With an Improved ZSVM6 Strategy

The quasi-Z-source inverter (qZSI) has been widely explored for renewable energy applications due to its superiority, e.g., higher boosting ratio and operational reliability, which is attained by inserting shoot-through (ST) states. As a conventional space vector modulation (SVM) method for the three-phase qZSI, the ZSVM6 method is easy to implement by dividing the ST time into six identical intervals. However, the instantaneous inductor current ripples of the qZSI with the ZSVM6 strategy are affected by the operating conditions, e.g., modulation index m and ST duty ratio dsh. In this article, the instantaneous inductor current ripples and the maximum current ripple in the qZSI with the ZSVM6 strategy under all operational conditions are explored in detail. The operational conditions are categorized into several cases according to the relationship among the duty ratios of the active states, null states, and ST states. More importantly, an improved ZSVM6 strategy is proposed to reduce the inductor current ripple for the qZSI, in which the maximum inductor current ripple is limited by making full use of the operational states. The proposed ZSVM6 strategy keeps the total ST time in a switching cycle while maintaining the axis-symmetry feature of the inductor current, but reduces the current ripple. Simulations and experimental results confirm effectiveness of the proposal when compared with the conventional ZSVM6 strategy for ripple current reduction.