Frequency domain modelling of traction PWM converters

In a previous paper by one of the authors (see J.A. Taufiq and J. Xiaoping, IEE Proc. B, Electr. Power Appl., vol.136, no.4, p.176-87, 1989), a frequency domain model (FDM) was described for calculating the DC side harmonics in a traction VSI drive. This principle has been extended to describe a FDM for an interlaced PWM converter drive system. Such a model, which can be 20-30 times faster than the corresponding time domain model, is useful for obtaining steady-state results of these drives for systems engineering. Typical results which can be produced are circuit and device waveforms, harmonic spectra and psophometric current. Such a fast simulation tool is particularly invaluable when a series of calculations are required over the entire speed range of the designed drive system. Results from an interlaced PWM converter fed inverter drive simulation are presented, including the effects of parameter asymmetry and load unbalance. A comparison is also made of the computer converter input current waveforms and those measured from a 1.5 MVA test rig. Computed and measured converter input current harmonic spectra are also compared to confirm the accuracy of the FDM