Compensation of fluctuating DC link voltage for traction inverter drive

In this paper, the behaviour of an inverter-induction motor drive system fed by a fluctuating DC link voltage is studied. The modulation process between the quasi-square wave switching function and the fluctuating DC link voltage generates beat voltages which produces large beat currents when the difference frequency approaches zero. This gives rise to serious problems for the motor; namely torque pulsation and motor heating. Compensation methods to suppress the low frequency beat current are discussed. A new compensation method based on volt-second equalisation is proposed and simulated.