Common Mode Voltage Reduction and Neutral-Point Voltage Balance for Quasi-Z-Source Three-Level Neutral-Point-Clamped Inverters

The three-level neutral-point-clamped (NPC) quasi-Z-source inverter (qZSI) is a promising power converter for renewable applications, where low total harmonic distortion and adjustable output voltage are highly demanded. Similar to the conventional transformerless three-level NPC inverter, common-mode voltage (CMV) and neutral-point voltage (NPV) issues should be addressed properly for the NPC-qZSI. Thus, this paper proposes a new control strategy for the NPC-qZSI to reduce CMV and balance NPV simultaneously by taking advantage of an additional control freedom enabled by the impedance network, i.e., three types of shoot-through states. The proposed strategy can achieve the CMV reduction by choosing the essential switching vectors with acceptable CMVs, while the NPV can be balanced by rearranging the chosen switching vectors in a switching cycle. Experimental tests are provided, which verify the effectiveness of the proposed strategy in terms of CMV reduction and NPV balancing.