Analysis of Shaped Pulse Transitions in Power Electronic Switching Waveforms for Reduced EMI Generation

Consideration of the higher order time derivatives of voltage and current transitions in power semiconductor devices enables the specification of “S-shaped” switching waveforms which offer an improved tradeoff between high-frequency EMI generation and switching losses. In comparison with the widely used first-order derivative trapezoidal switching waveform approximation, Fourier analysis of the proposed “S-shaped” waveform shows that it exhibits a 20 dB/dec steeper spectral gradient at high frequencies, resulting in a 20 dB greater reduction in high-frequency spectral content per decade increase in rise time. Numerical analysis of the proposed waveform shows that both peak and total RF power, employed as indicative EMI metrics, are reduced significantly with no increase in overall switching time. Experimental investigation of the effect of introducing a frequency-selective EMI transmission path shows that the overall trends in the relationships between time-domain waveform parameters and high-frequency spectral content are maintained, while the values of the waveform timing parameters which minimize the two EMI metrics are changed.