There are N sub-modules in a multilevel converter

and according to different modulation rules

N+1 levels (basic levels) or 2N+1 levels (full levels) can be achieved. The working mechanism and effects on the arm inductor of the two output levels is proposed

and the relationship between level generation and circulating current and capacitor voltage control is studied. Based on which

for the carrier phase position pulse width modulation (PWM)

a capacitor balance strategy based on PWM signals rotating is presented. With this strategy

the time of implementing the algorithm can be adjusted according to the need to reduce the change in the switching frequency caused by capacitor voltage balance. The conclusions and the strategy are verified with a 500 V dc input experimental platform.