Abnormal Voltage Compensation caused by Vertical Crossing in Phase-shifted PWM-based Cascaded H-bridge Inverters

This paper proposes a compensation method for abnormal voltage caused by vertical crossing in phase-shifted PWM-based cascaded H-bridge inverters (CHB) driven by digital signal processors (DSP). Vertical crossing occurs when the modulation wave is updated in any position other than the carrier's zero or peak, leading to the missed updates of PWM pulses. Since the vertical crossing generates abnormal CHB voltages, it leads to critical current surges. In this paper, the conditions under which the vertical crossing occurs in each cell of the CHB are predicted at every sampling instance. To suppress the occurrence of the vertical crossing, the modulation wave in a predicted cell of CHB is adjusted. Furthermore, the CHB output voltage error caused by the adjusted modulation wave is compensated by distributing this error to other cells, excluding the predicted cell. Through the proposed method, CHB can generate an accurate output voltage. The validity of the proposed method is verified by DSIM simulation results.