Using Double Fourier Series to Analytically Model Common-mode Voltage for Various Modulation Methods in Three-phase Voltage-source Inverters

The past literature, when investigating the common-mode current vs. switching frequency and switching profile, usually evaluated through simulation and experiment while lacking analytical models and tools. Some PWM methods might reduce the common-mode voltage (CMV) at some frequency, however, cause the increasing at other frequency points. Such overall merits and performance between different PWM patterns can only be evaluated by analytical models. In this paper, the analytical model of various PWM schemes with respect to common-mode (CM) signals are derived by Double Fourier Integral (DFI) analysis, especially for the active-zero state PWM (AZSPWM), which was simulated in the past while without any analytical model being presented. Both mathematical analysis and experimental results showed that AZSPWM does not necessarily reduce CMV in an overall frequency spam due to the induced sideband harmonics when comparing to some other modulation schems, for example, the discountinuous PWM (DPWM). The analitical tool can help provide a guidance on choosing different modulation method to achieve a practical and efficient combination based on various scenarios in motor drive applications.