Second Harmonic Voltage Suppression for LLC Converter in Dual-Stage Single-Phase Rectifier Based on Voltage-Oriented State Plane Feedforward Control

Second harmonic output voltage ripple in a single-phase grid-connected rectifier can degrade the system's performance. In this letter, a voltage-oriented state plane feedforward control is proposed to suppress the second harmonic output voltage ripple for the LLC converter, which serves as the backstage of the dual-stage single-phase rectifier. Herein, the desired switching frequency of the LLC converter is predicted online through geometrically simplified state plane analysis, and thus the voltage control loop gain at the second harmonic frequency can be increased. The proposed control strategy features a fast dynamic response and is immune to grid frequency deviation. Both simulation and experimental results fully confirm the theoretical analysis.