Research On Stability Of Photovoltaic And Energy Storage Microgrid System Based On Dc Voltage Control

With the rapid development of social economy,the contradiction between the increase of energy demand and the exhaustion of traditional energy supply has become more and more serious.The development and application of new energy has gradually become the focus of energy development.The distributed photovoltaic grid-connected power generation system includes new energy equipment and converter equipment,and the impedance of these equipment affects the stability of the system during operation.Therefore,the small signal analysis method is used to establish the impedance model of each component of the microgrid for analysis of system stability.It is of great significance for improving the utilization rate of solar energy and building new energy power generation system.Firstly,analyzes the control principle of the photovoltaic unit converter and the DC voltage control scheme of the photovoltaic inverter,deduces the mathematical model in detail and designs the parameters.The output impedance of Boost converter and the input impedance model of three-phase inverter are established.The stability of the cascade system is judged by dividing the power and load of the cascade system.The influence of different disturbances on the DC voltage of the photovoltaic inverter is analyzed.These disturbances include the DC voltage disturbance and the three-phase voltage unbalance disturbance on the AC side.In order to better improve the transfer efficiency of the photovoltaic system,this paper designs and optimizes the DC voltage amplitude.By adding the control method of the virtual positive and negative sequence admittance of the energy storage inverter STATCOM,the imbalance of the grid voltage is reduced.Method such as improved control strategy for voltage feedforward increase the stability margin of the system,thereby improving the system response speed and system immunity.Secondly,the output impedance model of PV inverter controlled by DC voltage loop and the output impedance model of droop-controlled energy storage inverter are derived.On this basis,the generalized Nyquist criterion is used to analyze the parallel stability of the entire system.The influence of DC side voltage amplitude and grid frequency disturbance on the droop-controlled photovoltaic and energy storage grid-connected system is analyzed,and finally an improved control method is given.Finally,a photovoltaic and energy storage microgrid system composed of two three-phase inverter systems and the Boost converter experimental platform have been designed and built with TMS320F28335 as the control core.Experiments were carried out to proved the feasibility of the proposed impedance modeling.verify the correctness of the improved control strategies.