Detailed Analysis of DC-Link Virtual Impedance-Based Suppression Method for Harmonics Interaction in High-Power PWM Current-Source Motor Drives

For high-power PWM current-source motor drive systems, due to the low converter switching frequency and the relative small dc choke for reduced cost/weight, the converters´ switching harmonics may interact through dc link and produce interharmonics in the entire system. Such harmonics interaction phenomenon may give rise to the system resonance at certain motor speeds, which degrades the grid-side power quality and generates excessive torque ripples on the motor side. The resonance caused by the harmonics interaction in high-power PWM current-source motor drives is investigated in previous study. In addition, to actively suppress such resonance, the basic idea of a dc-link virtual impedance-based suppression method has also been proposed. This paper extends the previous study to thoroughly analyze the mechanism and realization of resonance suppression by the dc-link virtual impedance-based method. The in-depth analysis shows that the dc-link virtual impedance-based method successfully enables the active interharmonics compensation capability of high-power PWM current-source drives, which is not addressed in previous researches. Moreover, simulations and experiments demonstrate that, by following the selection of coefficient in the suppression method discussed in this paper, the dc-link virtual impedance-based method can effectively enhance the attenuation effect of dc link in high-power PWM current-source drive systems so as to suppress the resonance due to the harmonics interaction under all resonance conditions.