Improved Space Vector Modulation of Quasi Z-Source Inverter to Suppress DC-Link Voltage Sag

The three traditional strategies ZSVM1, ZSVM2, and ZSVM6 have been commonly used to control the quasi Z-source inverter (qZSI). However, there is a serious problem that the dc-link voltage of the qZSI drops under light load, leading to the distortion of the output voltage and current of the inverter. The peak dc-link voltage also becomes much higher than its reference value, endangering the safety of the inverter and load. This paper proposes an improved SVM, namely M-ZSVM1, to suppress the dc-link voltage sag under a light load. Through analyzing the reason, the harm, and the influence factors of the dc-link voltage sag, the diode current interruption is seen as the cause of the dc-link voltage sag. Therefore, an asymmetric shoot-through state distribution method is presented to achieve the minimum current ripple, which can increase the diode current. The qZSI can work properly without the dc-link voltage sag under wide load range, improving the safety and reliability of the qZSI. Moreover, other improved ZSI topologies can also be controlled by the proposed strategy to suppress the dc-link voltage sag.