Influence of PWM Excitation on DC Winding Induced Voltage Pulsation in Wound Field Switched Flux Machines

The influence of the pulse width modulation (PWM) excitation on the DC winding induced voltage pulsation for the wound field switched flux (WFSF) machine is investigated in this paper. Firstly, the impact of the high frequency DC and AC winding current harmonics on the DC winding induced voltage pulsation is analyzed, which results in high frequency harmonics in the DC winding induced voltage. The co-simulation between electric circuit analysis and the electromagnetic field analysis is applied to verify the analysis of the DC winding induced voltage pulsation under PWM excitation. Both the current source supply mode and the PWM voltage source supply mode are applied and compared in the field-circuit co-simulation analysis. The results of the comparison indicate that PWM excitation will introduce harmonics with the frequencies close to the switching frequency and its multiples in the DC winding induced voltage, whilst the frequencies of low frequency harmonics remain unchanged. Four different wound field machines, i.e., WFSF machine designed at large scale, wound rotor synchronous machine, WFSF machine with single tooth winding, and the variable flux reluctance machine, are compared under PWM excitation. It is found that not only the analysed WFSF machine, but also other wound field machines suffer from additional DC winding induced voltage harmonics under PWM excitation. The field-circuit co-simulation is validated by experiments, including the open-circuit test and the on-load test. Finally, all the analysis and the simulations are validated by the experimental results.