Effects of Modulator-Injected Zero-Sequence Signals on System Stability in Three-Phase Voltage Source Converters

The modulator-injected zero-sequence signal (MI-ZSS) technique has found widespread application in modulating three-phase power converters, contributing to enhancements in efficiency, modulation range, and power quality. However, little attention has been given to its effect on system stability, mainly due to the neglect of modulator dynamics in traditional averaged models. This article bridges this gap by investigating the influence of MI-ZSS under carrier-based pulse-width modulation (CB-PWM) on the stability of three-phase voltage source converters (VSCs). A unified multifrequency small-signal model of the three-phase VSC is developed, taking into account CB-PWM dynamics under various MI-ZSS conditions. The model facilitates the analysis of the effects of MI-ZSSs on the system stability. The findings reveal that different MI-ZSSs result in distinct stability regions. Finally, experimental results verify the feasibility and correctness of the theoretical analysis presented above.