Optimized dual randomized PWM technique for reducing conducted EMI in DC-AC converters

Randomized Pulse Width Modulation (RPWM) has become a viable alternative to Deterministic PWM (DPWM). Indeed by spreading the power spectrum as a continuous noise, this new technique complies better with Electro-Magnetic Compatibility (EMC) standards for conducted Electro-Magnetic Interferences (EMI) and allows reducing the emitted acoustic noise in Variable Speed Drives (VSDs). The most popular RPWM schemes are Randomized Pulse Position Modulation (RPPM) and Randomized Carrier Frequency Modulation (RCFM). A combination of these two schemes (RCFM-RPPM) or Dual RPWM (DRPWM) has also been proposed. In this paper, we propose an Optimized Dual RPWM (ODRPWM) for the three-phase inverter. First, a modulating principle is proposed. Then, a mathematical model of Power Spectral Density (PSD) of the output voltage is developed. PSD analysis shows that the proposed scheme is more effective on spreading PSD. Moreover, this analysis reveals optimal parameters of randomization for a maximum spread of the PSD. The optimization problem is then modeled and solved using two powerful nonlinear methods: the trust region method and the simplex algorithm.

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