Design and Performance of a Transformerless Shunt Hybrid Filter Integrated Into a Three-Phase Diode Rectifier

This paper addresses 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 seventh-harmonic frequency, and a small-rated active filter based on a three-phase voltage-source pulsewidth modulation 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 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 cutoff frequency of high-pass filters for harmonic extraction.

I. Introduction

Attention has been paid to adjustable-speed motor drive systems intended for energy savings. They have already reached a wide range of applications, including high-performance drives as needed in rolling mills, and standard applications such as pumps, fans and others. Either a diode rectifier or a pulsewidth modulation (PWM) rectifier has been used as the front end of such a motor drive. Although the diode rectifier has no capability of regenerating energy, it provides a more efficient and much less expensive solution than the PWM rectifier. However, the diode rectifier produces a large amount of harmonic current, so that it does not meet harmonic guidelines or regulations. Hybrid filters consisting of dedicated passive and active filters connected in series or parallel have been published in the literature [1]–[11].