The Influence of LC Filter on the Current Control of PWM-Fed Induction Motor Considering the Effect of Back-EMF

Abstract

The high switch speed pulse width modulation (PWM) significantly improves the performance of induction motor. However, this mode of control generates PWM ripples and a wide spectrum of over-voltages at the motor terminal which stress the motor insulation and cause bearing current and electromagnetic interference (EMI). To solve this problem, LC passive filter is widely used because of its effectiveness on limit overvoltage and PWM ripples. This paper discuss the influence of LC filter on PWM-fed induction motor in a different view. The impedance of the motor is decided by its inductance and resistance in traditional research. In this paper, a more accuracy model is built up involving the effect of back electromotive force (EMF). Based on which, the situation of current control is investigated when the LC filter is employed. It is revealed that the inductance of the filter is the key factor of control bandwidth and a method to enhance current control bandwidth while avoid the loss of suppression ability of differential-mode PWM frequency components is given.

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“…These reasons leads to fluctuation of speed in open-loop or closed loop system whose sampling time is long and, as a result, uncomfortable acoustic noise and mechanical vibration inside vehicles may be generated [2]. Likewise, EMI noise is caused in the almost same reasons, switching harmonics and harmonics in control input in the control system [3]. Electromagnetic compatibility requirements in automotive are most stringent, inherent causes must be excluded as much as possible in motor design.…”

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“…Thus, in the various industry applications, torque ripple should be suppressed for low acoustic noise via dedicated control methods or initial system design [9][10][11][12]. Likewise, EMI noise is caused in the almost same reasons, switching harmonics and harmonics in control input in the control system [13]. Electromagnetic compatibility requirements in the automotive sector are most stringent; inherent causes must be excluded as much as possible in motor design.…”