Enhanced Control of Active Half-Bridge Type Four-Wire Vienna Rectifier under Unbalanced Grid Voltage Conditions

In order to enhance the Vienna rectifier's performance during three-phase unbalanced voltage conditions and mitigate the deviation of the capacitor midpoint voltage, a novel active half-bridge four-wire Vienna rectifier topology is proposed. This paper first introduces 3-D unbalance coordinate transformation to establish a control strategy for the active half-bridge four-wire Vienna rectifier based on PI control method, aiming at managing the zero-sequence voltage under unbalanced grid voltage conditions. Through the detection of second harmonic component of the output voltage, a control law is formulated to regulate the input current amplitudes, thereby eliminating the second harmonic ripple. Additionally, Multiple Proportional-Resonant (MPR) control is applied to regulate the capacitor midpoint voltage. Simulation results under unbalanced grid voltage conditions confirm the effectiveness of the proposed control strategy in eliminating three-phase current distortion, suppressing the deviation of capacitor midpoint voltage, and obtaining minimal rectifier output voltage ripple.