A New Active Output Filter (AOF) for Variable Speed Constant Frequency (VSCF) Power System in Aerospace Applications

In this paper a new active output filter" (AOF) for variable speed constant frequency power system in aerospace applications is proposed. The proposed AOF is envisioned as a power semiconductor filter block. In the proposed system the passive L-C output filter components are replaced by an H-bridge. The H-bridge is operated at high frequency to inject voltage harmonics to achieve a sinusoidal output voltage to the load. Advance wide band gap devices can be employed in the design of AOF block to obtain high performance with simultaneous reduction in size. The proposed AOF concept offers a significant reduction in size/weight compared to passive L-C. Further, in the presence of AOF the main VSCF inverter can be operated in a six-step and/or at a reduced PWM frequency. An example 156 kVA, 3-phase 400Hz system with the proposed AOF concept is evaluated via simulation with a corresponding passive L-C filter configuration. Experimental results on reduced kVA laboratory prototype are discussed.