three-phase active filter;  Nonlinear PID control;  Nonlinear tracking differentiator

By applying the nonlinear PID control theory to the discrete control system of three-phase voltage type active filter, by introducing the nonlinear combination of nonlinear tracking differentiator and PID control signal, the iterative format of the difference equation of the discrete control system based on the three-phase active filter controlled by nonlinear PID control is introduced, and the MAT-LAB simulation of the discrete difference equation of nonlinear PID control and the discrete difference equation of traditional PID control is carried out. The simulation results show that the use of nonlinear PID control can significantly improve the contradiction between the speed and overshoot of traditional PID control, improve the tracking speed of the system, have good robustness, and have good filtering effect.