Balance Technique for CM Noise Reduction in Critical-Mode-Based Three-Phase Soft Switching Bidirectional AC-DC Converters
The balance technique has proved to be an effective method for reducing CM noise in single-phase interleaved Totem-Pole PFC converters. By adding inductors on the return path and coupling the additional inductors with the original inductors, the balance conditions and therefore CM noise reduction are achieved. With optimal PCB winding inductor design and implementation, experimental results show a uniform 20 dB CM noise reduction from 150 kHz to 30 MHz.
The balance technique is extended to three-phase ac-dc systems in this work. A split capacitor branch is added at the dc side, and then the midpoint of the split capacitor branch is connected with the neutral point of the ac filter Y-capacitor by six additional inductors. After that, these six additional inductors are coupled with the six original inductors to achieve balance. Fig. 1 shows the circuit topology with the additional inductors for achieving balance.
For better effectiveness of CM noise reduction, external capacitors can be added to the system between the bus and the earth, or between the phase leg switch node and the earth, to fine tune the system parasitic capacitance and meet the balance condition. Fig. 2 shows the simulation results of CM noise, which indicates around 30 dB CM noise reduction is achieved with the balance technique in three-phase ac-dc system.