Design of a transformerless shunt hybrid filter integrated into a three-phase diode rectifier

This paper describes design and performance of a transformerless shunt hybrid filter integrated into a three-phase diode rectifier. The hybrid filter consists of a three-phase passive filter tuned to the 7th-harmonic frequency, and a small-rated active filter based on a three-phase voltage-source PWM converter. The validity of the system design is confirmed by experimental results obtained from a 400-V, 15-kW laboratory system. The experimental results show that the active filter plays an essential role in reducing supply harmonic currents. The THD (total harmonic distortion) of the supply current gets less than 5%. Moreover, the hybrid filter provides satisfactory transient performance as a result of having achieved an optimal design of circuit and control parameters including the dc capacitor voltage and feedback gains of the active filter, along with the cut-off frequency of high-pass filters for harmonic extraction.