The New Active Output Filter for Variable Speed Constant Frequency Aerospace Applications

A concept called “Active Output Filter” (AOF) for performing output filtering in switching converter is proposed. The methodology is based on voltage harmonic injection via a combination of H Bridge and minimized LC filter to cancel out the odd harmonics from a 400Hz square wave 3 phase inverter to achieve a pure sinusoidal output with modulation index of 1.27. Investigation reveals that AOF allows a substantial size reduction and gives competitive efficiency, as compared to passive inductor capacitor filter. Moreover, the main square wave inverter has a capability to regulate the output voltage depending on the Load requirements providing a wide range of modulation index. The operation principle of the concept is demonstrated for Variable Speed Constant Frequency (VSCF) high power aircraft application. The exploration lays a foundation for further investigation into the use of AOF concept for other power electronic converter systems