Improved natural balancing with modified phase shifted PWM for single-leg five-level flying-capacitor converters

Flying capacitor converters (FCCs), as most multilevel converter topologies, require a balancing mechanism of the capacitor voltages. FCCs have the valuable property of natural voltage balancing when a special modulation technique is used. The classic methods, like Phase-Shifted Pulse Width Modulation (PS-PWM), result in very slow balancing for some duty ratio ranges. Previous work showed that for a single-leg five-level FCC one time constant is infinite for a zero desired output voltage. In this paper, a modified PS-PWM scheme for a single-leg fivelevel FCC is presented which results in faster balancing over the total duty ratio range. The modified PS-PWM scheme is studied, resulting in an averaged voltage balancing model. This model is verified using simulations and experiments. The modified PS-PWM scheme solves the slow balancing problems of the normal PS-PWM method for odd-level FCCs, while maintaining the passive control property, and it provides a self-precharge capability