The Research Of Control Strategy On Parallel Single-Phase Photovoltaic Inverters

With the increasing of the energy crisis and the deterioration of the ecological environment,the development and utilization of new energy resources has received more and more attention.Solar energy is a renewable energy without pollution,and one of the major utilization is solar power generation technology.The parallel structure of multi inverter can effectively improve the capacity of solar installment and realize the large-scale utilization of solar energy.However,due to the difference of inverters' parameters and line impedance,the circulating current in parallel inverters is inevitable,which has a significant influence on the efficiency and reliability of the system.In order to suppress circulating current,the control strategy of parallel inverter has been paid great attention to by many scholars.And it has become a key point in the field of the inverter research.Photovoltaic inverter is the basis of photovoltaic parallel inverters.This paper firstly studies the main circuit of photovoltaic inverter in parallel system,then selects the topology structure of the main circuit,and complete the design of circuit.After that this paper analyzes the operation principle of the inverter,and gives the design steps of the controller.Simulation result confirms the correctness and validity of the previous design upon which an equivalent circuit of the inverter parallel system is established.The influence factor of circulating current is also analyzed.In order to suppress the circulating current,this paper analyzes the output power characteristic of inverter and the principle of droop control.Droop coefficient and transmission impedance are directly related to the stability of system.Therefore,this paper establishes the small signal model of parallel system.The droop coefficients have been chosen properly by comprehensive consideration of the stability and dynamic response capability,and the transfer impedance range is determined by root locus.Aiming at the problems existing in parallel system,such as errors in voltage and current tracking,poor anti-interference ability of the system and circulation suppression effect,a novel current sharing control method is proposed.Virtual negative impedance technique is used to share the power accurately.And the transfer impedance is also designed to meet the requirements of stability of the system.Double quasi proportional resonant controller is applied to realize zero steady-state errors control of the voltage and current,which will reduce the deviation of output voltage and current,and improve the stability of the system.The simulation result shows that the parallel inverter system can effectively implement the power sharing and the circulating current suppression so as to improve the stability of the system.