Active Power Decoupling for High-Power Single-Phase PWM Rectifiers

Single-phase pulsewidth modulation rectifiers suffer from ripple power pulsating at twice the line frequency. The ripple power is usually filtered by a bulky capacitor bank or an LC branch, resulting in lower power density. The alternative way is active power decoupling, which uses an active circuit to direct the pulsating power into another energy-storage component. The main dc-link filter capacitor can, therefore, be reduced substantially. This paper proposed a new scheme of active power decoupling. The circuit consists of a third leg, an energy-storage capacitor and a smoothing inductor. The topology combined the advantages of high energy-storage efficiency and low requirement on control bandwidth. Both the pulsating power from the ac source and the reactive power of the smoothing inductors are taken into consideration when deriving the power decoupling scheme. The active power filter's (APF) capacitor voltage control system consists of inner loop pole-placement control and outer loop proportional-resonant control. To enhance the steady-state performance, the capacitor voltage reference is modified in a closed-loop manner. Simulation and experimental results show that the proposed APF scheme has good power decoupling performance and is more suited for high-power applications where switching frequency is limited.