Voltage-balancing method for stacked multicell converters using phase-disposition PWM

This paper presents a voltage-balancing method for stacked multicell converters (SMCs) based on phase disposition pulsewidth modulation. A cost function is evaluated to select the optimum state from a pool of redundant possible ones at each voltage level. It is demonstrated that, if sawtooth carriers are used for modulation instead of standard triangular ones, significant reduction in the switching frequency and the associated power losses of the power devices can be achieved without affecting the voltage-balancing capability. Experimental results from a seven-level SMC laboratory prototype are provided to verify the proposed voltage-balancing method against linear and nonlinear loads, as well as under transient conditions.