Practical issues in parallel operation of one-cycle controlled PFC rectifiers

Parallel operation of three-phase power factor corrected (PFC) rectifiers extends the power range to a much higher level and allows modular design. However, some practical issues, such as current sharing and power distribution, circulating currents, and dynamic performance, could be the potential problems. This paper first presents a simple equation for paralleled One-Cycle Controlled (OCC) PFC rectifiers with uneven power ratings. Then an equivalent circuit for circulating current is studied and the validity of OCC parallel method for reducing circulating currents is discussed. At last, an improvement is proposed to the traditional PI compensator to accelerate the transient process when the old master rectifier drops off and a new master establishes due to fault. Two OCC PFC rectifiers were built and experiments have been done for verification.