An Adaptive Digital Notch Filter Based on Grid Impedance Estimation for Improving LCL Filter Peformance

In the grid-connected system, LCL filters are playing an important role in eliminating the switching frequency compared with the traditional LC filter. Digital notch filter can be used for solving the resonant frequency problem by cancelling the resonant peak. This paper presents an adaptive digital notch filter based on an estimation controller for the grid impedance and the parameters of the notch filter can be adjusted by the estimated grid impedance value. Moreover, the notch filter design and the system stability is also presented in theoretical analysis. Finally, the simulation results shows effectiveness of the estimation algorithm and digital notch filter's function for active damping.