Research On Single-Phase Z-Source Grid-Connected Photovoltaic Inverter

Energy and environment problems have aroused universal concern of the whole international community. In order to realize the sustainable development of energy and environment, photovoltaic technology has been viewed by many countries as a feasible solution. Inverter, which is a key part of PV system, has always been a focus of research. Z-source inverter, an inverter equipped with Z-source network which has just been proposed in recent years, has aroused attention of domestic scholars because of its advantages over traditional inverters. The paper intends to study the application of single phase Z-source inverter in PV grid-connected system.First, the topology, working principle and control method of inverter bridge shoot through state of Z-source inverter is introduced. Then we analyze an abnormal working condition of Z-source inverter and propose a parameter setting which can avoid such abnormal working condition. According to the features of Z-source inverter, we make an equivalent analysis of circuits in a shoot through state and in a non-shoot through and presents the formula of its state space. Then we make a model analysis of Z-source network based on state space average method.According to the features of Z-source network and the properties that PV grid-connected system must have, a control system is designed for single phase Z-source PV grid-connected system inverter. The control system is comprised of double closed-loop system:inner loop control of grid-connected current and outer loop control of Z-source network capacitance. Dc link voltage control is realized by means of controlling Z-source capacitance voltage. Because the paper uses the method of constant voltage maximum power point tracking, we only need to match the output voltage of photovoltaic array with dc link voltage of inverter bridge. As long as the dc link voltage of inverter bridge is in steady state, we can successfully realize the maximum power point tracking. The paper also analyzes the designing principle of inductance, capacitance and grid-connected inductance. Based on the analyzed parameter design formula and the design method of control system, a simulation is carried out on single phase Z-source PV grid-connected system by MATLAB7.1. Then we analyze the simulation results, summarize the existing problems and propose future plans for research.Finally, we summarize the whole system and look forward to the future development of Z-source inverter.