Performance Comparison of Variable-Angle Phase-Shifting Carrier PWM Techniques

This paper analyzes the performances of different carrier phase-shifting pulse width modulation (PWM) techniques to be used with a multilevel cascaded H-bridge converter in case of unbalanced operational conditions. In fact, in many practical applications, the ideal condition of equal dc voltages and equal reference signals for each H-bridge cannot be achieved. In such conditions, the conventional carrier phase-shifting PWM technique loses its harmonic canceling capabilities and then the multilevel ac voltage harmonic quality is deeply affected. To overcome this limit of the original technique, different variations have been proposed. All of them still rely on the carrier phase-shifting concept and propose to use a different value of the shifting angle for each carrier (unlike the original technique) whenever unbalanced operational conditions occur. In this paper, the three main solutions proposed over the last years to extend the capabilities of the carrier phase-shifting PWM technique are compared. The analysis is focused on a three-cell cascaded H-bridge converter. Simulation and experimental results are presented.