Design and Analysis of Sigma Z-Source Inverter for PV Applications

Traditional Voltage Source Inverter (VSI) produces lesser output voltage than the input and causes shoot-through due to the gating of the semiconductor device connected in same leg. The ZSI is used to overcome the inadequacies of VSI. The ZSI has been extensively used in electric drives, PV system and UPS. The conventional ZSI suffers some disadvantages like restricted boost capability, discontinuity in input current and large inrush current. These limitations are overcome by using a transformer which replaces the inductor in the impedance source network. In high-voltage gain applications, the single transformer-based ZSI topologies requires more turns ratio which requires large size transformer. For improving the boost capability, the TZSI is used. The Z-source network of the TZSI constitutes two transformers with low turns ratio. TZSI has certain demerits such as restricted boost capability, high inrush current and discontinuity in the input current. However, TZSI requires high turns ratio to increase the boost capability. Thus, the modified ZSI, i.e. sigma ZSI is investigated in this paper. The sigma ZSI has the advantage of having reduced turns ratio with enhanced boost capability.