Quasi-Two-Stage Multi-Functional Photovoltaic Inverter with Power Quality Control and Enhanced Conversion Efficiency

A novel quasi-two-stage multifunctional inverter (QMFI) for photovoltaic (PV) applications is proposed in this article. With the help of the quasi-two-stage architecture, part of active power can be directly transferred from PV arrays to the grid or load within a single power conversion stage and hence improve the efficiency. In addition to active power transfer, both the realization of maximum power point tracking (MPPT) and compensation of nonactive current (i.e., reactive, harmonic, or unbalanced current) of the QMFI are considered. A mathematical model of the QMFI is presented to guide the control parameter design. Meanwhile, an analysis model based on the rotating frame is proposed to derive the space vector pulsewidth modulation strategy of the QMFI, and also, offer straightforward insight into the influence of nonactive current compensation on quasi-two-stage active power flow. Compared with traditional solutions, the QMFI can realize active power delivery with higher efficiency and also keep functions of achieving MPPT and enhancing power quality. The feasibility and effectiveness of the proposed solution are verified with a 3-kVA prototype.