Modulation Techniques for Common-Mode Voltage Reduction in the Z-Source Ultra Sparse Matrix Converters

Common-mode voltage (CMV) is known as a major cause of premature motor failures. The form and amplitude of the CMV generated by any converter depends on both the circuit topology and modulation technique. Among single stage ac-ac converters employed in drive applications, the Z-source ultra sparse matrix converter (ZSUSMC) is a desirable choice due to reduced number of switches in its structure and voltage boosting capability. Based on these considerations, this paper aims to: 1) theoretically determine and compare the CMV of the ZSUSMC with four well-known impedance networks, namely, cascaded, switched-inductor, quasi, and series, in its structure and 2) propose modulation techniques for CMV reduction in the ZSUSMCs. To this end, first, it is shown that the ZSUSMC, depending on the impedance network used in its structure, provides more freedom to choose from redundant switching states compared to the ultra sparse matrix converter. Then, by taking advantage of this feature, novel modulation strategies that attenuate the CMV without affecting the boosting capability are developed. The proposed modulation schemes are based on avoiding the switching states most contributing to the CMV during a switching period. Through hardware-in-the-loop studies, the effectiveness of the proposed modulation strategies in reducing the CMV of the ZSUSMCs is verified.