Virtual Vector Modulated Hybrid 2/3-Level Z-source VSI for PV Applications

Abstract

Hybrid two/three level (2/3L) voltage source inverter (VSI) has been introduced as an alternative to conventional two level (2L) and three level (3L) VSIs. The inverter uses only ten switching devices but results in elimination of all the medium voltage vectors of the 3L inverter. On the other hand, it increases twelve switching states in the form of small vectors compared to 2L inverter. In this paper, a new virtual vector (VV) modulation for hybrid 2/3L VSI is presented. The proposed modulation uses both the small vectors in each switching cycle for entire modulation index range. Two switching sequences derived from the VV modulation are analyzed in detail for higher modulation range. The hybrid 2/3L VSI was also operated with a Z-source impedance network for interconnecting low voltage sources like photo voltaic arrays (PVAs). Unlike the existing modulations developed for hybrid 2/3L VSI, the proposed VV modulation can be directly applied to operate the hybrid 2/3L Z-source VSI. Minimum number of device commutations are retained even with the insertion of shoot-through switching states. Performance of the proposed VV modulated hybrid 2/3L Z-source VSI is verified in MATLAB SIMULINK and the results are provided.