Random modulation techniques with fixed switching frequency for three-phase power converters

This paper proposes a new family of random modulation techniques for three-phase power converters which operate with a fixed switching frequency. The techniques are based on adjusting the duration of the zero-vectors or adjusting the three PWM pulses in a switching period. Three methods are selected for experimental tests because they preserve the fixed switching frequency known from standard PWM techniques. The new methods are also compared with a classic random modulation and with fixed switching frequency modulation. Voltage, current and acoustic noise spectra are used for comparison and it is concluded that two of the techniques are especially useful at lower fundamental frequencies. The techniques can substitute classic random modulation techniques with variable switching frequency in some applications.