Computation-Efficient Variable Angle Phase-Shifting PWM Method for Cascaded H-Bridge Converters

When unbalances happen among the cells of a cascaded H-bridge (CHB) converter, variable angle phase-shifting (VAPS) pulse-width modulation (PWM) methods can be employed to improve the total harmonic distortion (THD) performance. However, as conventional methods are based on optimization algorithms which require a huge amount of evolutionary computations, the optimal carrier phase-shifting (PS) angles cannot be timely updated with a common standard digital signal processor (DSP) or microcontroller. During the period when the optimization is not finished, the THD of the total output voltage may significantly increase, bringing about higher power losses. Thus, a computation-efficient VAPS PWM method is proposed in this paper. With multiple calculation units (CUs) implemented in field programmable gate arrays (FPGAs), multiple calculations can be executed in parallel, significantly improving the optimization speed of the VAPS PWM method. Experimental results on a 4-cell CHB converter have demonstrated the effectiveness of the proposed method.