Theoretical Study of Rampwise DPWM Technique to Reduce Motor Acoustic Noise

Motor acoustic noise generated near living environments, such as elevators and electric vehicles, may cause discomfort. In order to reduce the acoustic noise, the switching frequency is set to the high side of the audible frequency range. In this case, however, the switching loss is increased. The conventional discontinuous pulsewidth modulation (DPWM) method is widely used since it can reduce the switching loss drastically. However, it produces larger acoustic noise than the conventional sinusoidal pulsewidth modulation method. The authors have previously proposed “Rampwise DPWM technique,” which can reduce both acoustic noise and switching loss. In this article, the line–line voltage with the proposed Rampwise DPWM technique is expanded into a real-valued Fourier series, and the frequency characteristics are analyzed. It is theoretically confirmed that the rampwise part in the Rampwise DPWM technique can achieve the reduction of motor acoustic noise. Furthermore, the reduction effect of motor acoustic noise with the Rampwise DPWM technique is theoretically and experimentally verified.