Controller design for quasi-Z-source inverter in photovoltaic systems

Abstract

The voltage-fed quasi-Z-source inverter (qZSI) has been presented advantageous for photovoltaic (PV) applications. This paper further develops the closed-loop controller for the qZSI operating in both stand-alone and grid-connected modes. Regarding to the limitation between the modulation index and shoot-through duty ratio, guideline of the reference selection for capacitor voltage to minimize the voltage stress imposed on switching legs has been illustrated. A two-stage control method operating in both stand-alone and grid-connected mode is presented. Closed-loop control for the output voltage/current has been performed; simultaneously, capacitor voltage in the qZSI-network is fed back for different purpose under the two operation modes. MPPT has been implemented in the grid-connected qZSI through the proposed controller. Both stand-alone and grid-connected operations of the qZSI have been implemented and their simulation and experimental results are presented for theoretical validation.