Intermediate 60^° Modulation with Real-time Gain Correction based on Phase-shifted Carrier

Low carrier ratio operation is a typical working condition and common feature of medium voltage converters. However, with the decrease of the carrier ratio, the THD of the AC side current and the low-order harmonics increases significantly, so it is necessary to optimize traditional pulse width modulation. The intermediate 60° modulation is a commonly used modulation under extremely low carrier ratio, but this method requires strict synchronization of the zero-crossing point of the carrier and the modulation wave, and the gain correction period is one fundamental wave period. In this paper, an intermediate 60° modulation with real-time gain correction based on phase-shifted carrier is proposed. This method does not require deforming the carrier, and corrects the modulator gain in real time by injecting common-mode voltage. In addition, the waveform quality of the proposed method is basically the same as that of the traditional intermediate 60° modulation.