Influence of the modulation method on the conduction and switching losses of a PWM converter system

The dependency of the conduction losses of a bridge leg of a PWM power converter system with a high pulse rate on the shape of the phase modulation functions is explored. This is done for modulation methods which are optimized with respect to minimum harmonic current RMS values. The results are compared to the results gained for simple sinusoidal modulation. Besides the conduction losses, the switching losses of the electric valves are calculated. Deviations from the classical sinusoidal modulation are only obtained for modulation methods for which the output voltage is formed by a cyclic change via only two active and a third nonswitching bridge leg. As the calculations show, these modulation methods allow a significant increase of the effective switching frequency. This effect is dependent on the phase angle between the fundamental of the converter output phase voltage and the converter output phase current; for this comparison, equal switching losses, as for the simple sinusoidal modulation, are assumed.<
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