Research On Cascaded Quasi-Z Source Inverter For Grid-Connected PV System

Abstract:The problems of energy crises and environmental pollution that brought by traditional energy generation need to be solved, the appearance of renewable energy power generation is used to ease the urgent needs of humanity, among of them, the photovoltaic power generation has the most development potential and has been widely concerning. Inverter is the core part of power generation system and it got the focus of academic attention in recent years. Aiming at the issues of low utilization rate of PV cells and high harmonics of grid-connected current, improved inverter topology is an effective solution. In the existing inverter topologies, cascade quasi-Z-source inverter topology has superior performance, it combines the advantages of the cascade multi-level inverter and quasi-Z-source inverter and this topology can improve the efficiency and power quality of grid-connected PV system.This paper studies the cascade quasi-Z-source inverter, and it is applied to grid-connected PV systems. The master-slave control strategy is proposed according to the circuit structure and control objectives after analyzing the structure and working mechanism of photovoltaic power generation system based on cascade quasi-Z-source inverter. To achieve stability, reliability and high efficiency of the system, this paper adopts a plurality of closed-loop control, including PV array output voltage loop, dc-link voltage loop and the grid current loop.The closed-loops control achieves MPPT and balance of bus voltage in cascaded cells, meanwhile, makes sure the AC side current is the same phase with the grid voltage so that the power factor is1. Furthermore, a modified carrier phase (CPS-SPWM) modulation method is adopted to output multi-level waveform and improve the power quality.A simulation model of the grid-connected PV system based on cascade quasi-Z-source inverter is built in the MATLAB/SIMULINK. The analyses of simulation results showed that the proposed control strategy can well meet the predict targets and the design of the controller is rational. The amounts of figures, tables and references are86,5and68, respectively.