Research On The Composite Control For PV Grid-Connected And Energy-Storage Based On Quasi-Z Source Inverter

As an important aspect in the field of new energy development, the photovoltaic(PV)power generation has been widely paid attention to by domestic and foreign scholars.Affected by climate change and other uncertain factors, the output power of the photovoltaic power generation system has the typical intermittent and fluctuant characteristics. Batteries and other storage devices can refrain the intermittent and fluctuant characteristics of the output power of the photovoltaic power generation with their control methods. Therefore, the energy storage technology has an important role in the new energy generating system.Firstly, a new type of the power converter named Quasi-Z source inverter(QZSI) is analyzed in this paper. The QZSI is applied to the photovoltaic power generation system,which can not only meet the demand of boosting input voltage for the converter, but also decrease the switching devices of the circuit. A unique Quasi-Z source impedance network is applied to the QZSI, which can make the shoot-through state to appear in the inverter.Then the output current wave form is improved because there is no dead band and the reliability of the system is enhanced.Secondly, the research on the characteristics of the photovoltaic grid-connected inverter based on the Quasi-Z source inverter with battery is conducted in this paper. The composite control method for PV grid-connected and energy-storage based on Quasi-Z source inverter is put forward. In this method, the different control strategies are applied with the different battery states to achieve the maximum utilization of the energy efficiency of the photovoltaic cells, enhance stability of the grid-connected power and improve the using environment of the battery. In the Quasi-Z source inverter system with energy-storage device, because of its special circuit topology, the fluctuant peak of DC-link voltage is caused by the change of external environment, and the grid-connected current is perturbed. Faced with these problems, the strategy of the variable-parameter PI control of the grid-connected current is proposed, and the superiority of the variable-parameter PI control is verified through the theory analysis.Finally, the simulation of the control strategy researched in this paper is achievedbased on MATLAB/Simulink. Then the experimental platform of the Quasi-Z source three-phase inverter with energy-storage device is set up. Based on the experimental platform, the control strategy proposed in this paper is verified. According to the simulation and experiment, the control strategy proposed in this paper can not only achieve the maximum utilization of the energy efficiency of the photovoltaic cells, but also maximize the protection of the battery, and the quality of the grid-connected current can be improved by using the strategy of the variable-parameter PI control for the grid-connected current.