Abstract: To solve the problem of grid voltage distortion affecting the current control performance of photovoltaic inverter, a current control strategy based on proportional-integral-resonant (PIR) regulator is proposed. Firstly, the control structure of photovoltaic inverter with inner current-loop and outer DC voltage-loop is determined. PIR regulator is used to suppress the grid voltage distortion or disturbance in inner current-loop and track the fundamental current. Due to the high orders of the LCL filter and PIR regulator in the photovoltaic inverter, there are many problems in the design of control parameters. Then, a parametric design method of PIR regulator based on the discrete-time root locus is proposed, which avoids the performance deviation or unstability of the regulator when the regulator parameters based on continuous domain are directly applied to the digital controller. Analysis results show that the design parameters can still make the system have a good adaptability during the changes of the grid frequency and LCL filter parameters. Finally, a simulation model based on Simulink verifies the feasibility of the current control strategy based on PIR regulator and the correctness of designed controller parameters.

Key words: photovoltaic inverter, grid voltage distortion, LCL filter, proportional-integral-resonant (PIR) regulator, discrete-time root locus