Abnormal Voltage Suppression Method for Multi-Sampled Cascaded H-Bridge Inverters Based on Phase-Shifted PWM

This paper proposes a suppression method for abnormal voltage caused by vertical crossing in phase-shifted PWM (PS-PWM)-based multi-sampled cascaded H-bridge (CHB) inverters. In PS-PWM-based CHB, multi-sampling is used to increase the bandwidth of the control loop and to improve transient and steady-state performance. However, in a multi-sampling, missed updates of PWM pulses occur due to vertical crossing, leading to an abnormal output voltage of the CHB. In this paper, the magnitude of CHB voltage error caused by vertical crossing is derived, and the influences of the carrier period on vertical crossing is analyzed in detail. Furthermore, to suppress the abnormal voltage, the occurrence of vertical crossing is predicted by utilizing the values of modulation waves and carriers at each sampling. Once a vertical crossing is predicted, the modulation wave is modulated to update the PWM pulse. The validity of the proposed method is verified by three-cell CHB experiment results.