Flux and loss distributions in a typical stator core under PWM voltage excitation

Summary form only given. Pulse width modulated (PWM) inverter power supplies are widely used for induction motors drives used for variable speed systems due to easy control methods and low cost. When induction motor stator cores are energised by PWM power supplies, the laminated electrical steel core is subjected to additional magnetic losses. In most previous work, the Epstein square has been used when assessing magnetic material under PWM voltage supply. Recently the PWM inverter power supplies, wide uses of other electronically generated voltage waveforms have made many electrical steel producers and motor manufacturers concerned about additional iron losses due to flux distortion. Orthogonal search coils are located on one lamination to detect components of flux density. The search coil positions are designated S1-S4 behind a slot and T1-T4 behind a tooth. The pack of laminations are magnetised either with the 3-phase sinusoidal voltage source or the PWM supply. The authors show that PWM excitation leads to maximum 20% loss increase with respect to sine wave excitation in a typical induction motor stator core. The loss increase is large in the teeth and smaller at the edges of the stator core lamination. The switching frequency plays important role on loss increase by causing ripples on flux density waveform.