The useful bandwidth of power electronic switching waveform measurements is limited by the finite resolution of measurement instrumentation and the spectral characteristics of switching waveforms, which exhibit a steep roll-off with increasing frequency. This limits the use of such measurements in EMI generation analysis, simulation and prediction. A method combining PC-based offline data processing and high-pass filtering of the waveforms prior to measurement allows the useful measurement bandwidth to be extended to 100 MHz in the case of a 1200 V, 15 A IGBT operating under realistic conditions. When utilised with commercially available current probes and passive voltage probes, this method offers high-fidelity measurements. However, it is more difficult to obtain repeatable measurements with high-voltage differential probes. The resulting spectra of IGBT collector-emitter voltage and collector current waveforms are presented; the increased bandwidth allows the high-frequency spectral gradient of −60 dB/decade to be observed across the 30–100 MHz band most critical for radiated EMI generation in IGBT-based power converters. The effect of series gate resistance variation is thus apparent, and spectral evidence is provided for the 30–100 MHz band being dominated by the turn-on transients with small gate resistances, and by the turn-off transients with large gate resistances.
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