Research on active and passive overvoltage suppression techniques for inverter-fed motor drive systems

Abstract

Inverter-fed AC motor drive systems play a very important role in both domestic and industrial applications because of their energy efficiency, control flexibility and the ease of maintenance. However, the fast-switching pulses generated by the variable frequency drive (VFD) cause overvoltage on the motor terminals, motor stator windings, as well as a high common-mode current through the motor bearings. Such destructive voltage spikes and current would damage the motor insulation system and cause premature failure of the bearings. To protect the motor against these problems, many passive filter networks such as sine wave filter, RLC filter and RC filter have been developed. However they are generally energy inefficient or cannot alter the wavefront of the pulses at the motor terminal to improve the inter-coil and inter-turn voltage distributions in the motor and reduce the common-mode current. To provide a full protection to the motor against the long transmission line effect on the inverter-fed motor drive systems, both active and passive filter solutions are investigated. An active motor terminal filter that can perform the same functions as the commonly-used passive overvoltage suppression filters is proposed. It has less power dissipation compared with the commonly-used RLC filter and RC filter. To further improve the energy efficiency of the active filter, an energy recovery function is introduced into it. The energy gained from suppressing motor terminal voltage surges is regenerated back to the whole system so that the power loss of the filter is greatly reduced. Besides, a generalized model that can study the interactions between the overvoltage suppression filter and the inverter-cable-motor system has been formulated. Based on the model, ideal impedance characteristics for the inverter-side and motor-side filters are given. A low-loss near-ideal "RL-plus-C" filter is proposed and studied. Apart from suppressing overvoltage at the motor terminals, it is able to prolong the rise time of the motor terminal voltage to suppress the voltages overshoot inside the motor windings and reduce the common-mode current through the motor bearings. Its performance has been compared with the commonly-used RC and RLC filters. Experimental results have confirmed the theoretical predictions. Most importantly, the proposed filter has low power dissipation. It can remedy the major drawback of classical passive filters for overvoltage suppression.

Date of Award	15 Jul 2014
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Shu Hung Henry CHUNG (Supervisor)