Impact of Adjustable Speed PWM drives on Operation and Harmonic Losses of Nonlinear Three Phase Transformers

Impact of harmonics generated by adjustable speed PWM drive systems on the losses and power quality of three- phase nonlinear transformers is investigated. The combined effects of transformer magnetic core nonlinearity, non-sinusoidal input excitation, asymmetric operation, as well as harmonics injected by the PWM action of the drive are included and analyzed. A time domain nonlinear model for three-phase three- leg transformers is implemented and used to compute non- sinusoidal input and output waveforms in the presence of PWM drives. Additional power losses due to harmonics generated by the iron core, non-sinusoidal (input) excitation and nonlinearity of drive system are computed.