Research On Two-current Closed-loop Control Strategy Of Three-phase Photovoltaic Inverter

With the development of society and economy,the pollution caused by traditional energy sources is becoming more and more serious.The adjustment of energy structure is more and more important in the world.Because of its renewable and non-pollution advantages,solar energy has been paid more and more attention.As the core component of photovoltaic power generation,grid-connected inverter has become the focus of research by experts at home and abroad.In this paper,the maximum power point tracking control strategy,the resonant damping strategy of LCL filter and the double-current closed-loop control strategy of three-phase LCL two stage non-isolated photovoltaic grid-connected inverter system are studied and analyzed in depth.Major contributions of this paper are:Firstly,the mathematical equivalent model of photovoltaic cells is established,and the output characteristics of photovoltaic cells under different temperature and light conditions are simulated and analyzed,and several traditional maximum power point tracking control strategies are analyzed theoretically.A control strategy combining constant voltage tracking method and variable step conductance increment method is adopted.The good dynamic performance of the control strategy is verified by simulation analysis.Secondly,aiming at the resonance problem of LCL filter,the advantages and disadvantages of active damping strategy and passive damping strategy are analyzed in detail.Based on the active damping strategy,a double-current closed-loop control strategy is adopted.The capacitor current feedback is used as the internal current loop to suppress the high-frequency resonance of the LCL filter.The grid-connected current is used as the outer loop of the current.In order to realize the non-static error tracking control of the AC signal,the PR controller is used in the outer loop of the current.In order to solve the problem of small gain of PR controller at non-resonant frequency,a voltage feedforward link is introduced to suppress the influence of grid voltage on grid-connected current.The photovoltaic grid-connected inverter system with double-current closed-loop control strategy is verified by simulation.The grid-connected inverter system can realize gridconnected per unit power,and the grid-connected current has the advantages of small error and small THD.Finally,combined with the laboratory conditions and safety considerations,the 150W/22 V low-voltage and low-power experiments are carried out.The main circuit parameter design and power device selection of the experimental prototype are described in detail,the hardware control circuit based on TMS320F28335 is constructed,and the sampling circuit,drive circuit and protection circuit are analyzed and explained.The design of the software program of the control system is explained and the flow chart of the main program is given,and the effectiveness of the control strategy is verified by the analysis of the experimental results.