A Multifrequency Equivalent Harmonic Modeling Method for Digital Discontinuous PWM

Compared to continuous pulsewidth modulation (CPWM) strategies, scattered output harmonics introduced by discontinuous PWM (DPWM) can cause increased loss, vibration, and noise in motor drive applications. An accurate assessment of the harmonic spectrum is crucial for comparing and improving the output performance of DPWM. However, solving the frequency-domain analytical expressions of output harmonics for DPWM is challenging due to its discontinuous piecewise characteristic. In this article, a multifrequency equivalent output voltage harmonic modeling method for DPWM of digitally controlled two-level voltage source inverter (VSI) is presented. By equating discontinuous DPWM with a multifrequency continuous modulation process, a scalable output voltage harmonic model is established. The model utilizes double Fourier integrals and considers both symmetric regular sampling (SRS) and asymmetric regular sampling (ARS) processes. Using the presented model, detailed frequency-domain analytical expressions for the six most widely employed DPWM schemes are given. In addition, the characteristics and performance of the output voltage harmonic spectrum are investigated through analytical analysis, simulations, and experiments. The verification results demonstrate that the modeling method provides an accurate estimation of output voltage harmonics for digital DPWM at various carrier ratios.