Common Mode Voltage Reduction in Three Phase Inverter using Pre-Calculated Harmonic Eliminated PWM Method

Abstract

Common Mode Voltage (CMV) produced in Pulse Width Modulated (PWM) inverters causes premature failure of the motor bearings. Therefore CMV has to be reduced. Pre-calculated Harmonic Eliminated PWM (PHEPWM) scheme is proposed to reduce the CMV in three phase inverter. The accurate switching angles have to be calculated by solving nonlinear equations. The switching angles for the pre-calculated harmonic elimination technique are calculated by using Newton-Raphson algorithm. The proposed modulation scheme is evaluated and tested at various switching frequencies for different modulation index. With this PHEPWM it is possible to eliminate the lower order harmonics, 5th, 7th , 11th, 13th, 17th, 19th, and 23rd from the inverter output voltage for any desired value of the fundamental component in for any desired modulation index. The CMV in inverter using PHEPWM method is compared with CMV produced using classical Sinusoidal PWM (SPWM) method.