The control of machine current harmonics in load commutated inverter induction motor drives

It is necessary to regulate the harmonic content of current in induction motors when fed by load commutated inverters in order to minimise the effects of electrical resonance, motor heating and torque pulsations. The use of speed avoidance bands, resonant frequency shifting and filtering/damping may provide an appropriate solution to harmonic problems but it is becoming more common to rely on purely electronic means of harmonic compensation. The use of pulse width modulation harmonic elimination techniques in drive power convertors is well known but it is difficult to achieve theoretically ideal waveforms when using current source topologies. This work describes some of the means of controlling motor harmonics, with specific reference to the compromises imposed by practical power circuit and machine limitations. Performance-related effects, as measured on working drives and using the results of simulations, are presented