Control strategy for harmonic suppression in LCL-type photovoltaic grid-connected inverter based on capacitor voltage feedforward

Abstract

The grid voltage feedforward control strategy has a significant suppressing effect on harmonic currents caused by grid voltage distortion, with its performance dependent on the accurate measurement of grid voltage. The presence of weak grid impedance and transformer leakage inductance makes it difficult to accurately measure grid voltage, thereby limiting the control effectiveness. To address this problem, this research suggests a control strategy based on capacitor voltage feedforward, in which the feedforward signal is capacitor voltage rather than grid voltage. The feedforward function of the proposed strategy consists of a second-order differential term, a first-order differential term, and a proportional term. The first-order differential term cancels out the active damping term, thereby saving the system one current sensor. Since the proposed control strategy alters system stability by using internal system signals as feedforward variables, this paper introduces a low-pass filter in the second-order differential term to correct the equivalent impedance, ensuring stable system operation. The proposed method’s effectiveness was validated through a simulation experiment platform established in MATLAB/Simulink.