ACTIVE POWER FILTERS USING RESONANT POLE INVERTERS

Although the concept of active filters is well known, it has not been possible to apply the concepts to realistically sized systems. A typical application such as the harmonic compensation of a 500-kW converter load would require PWM inverters rated at 50-100 kVA and capable of switching at frequencies in the 8-10 kHz range, which is a difficult task given the state of the art in BJT and GTO inverter technology. This paper proposes the use of a new soft switching inverter topology (the resonant pole inverter (RPI)) for harmonic compensator realization. Using resonant transitions to minimize switching losses, the topology is suitable for use with GTO's and other gate turn-off devices. Switching frequencies in the order of 10-20 kHz at multikilowatt power levels are feasible. A current-mode modulation strategy is proposed and is seen to realize good spectral characteristics. The paper is supported with extensive simulation and experimental results at a 10-kVA GTO resonant pole inverter switching between 10-20 kHz.