About the DC-link capacitors voltage balance in multi-point clamped converters

The multi-point clamped converter (MPCC) represents an interesting technical solution to overcome the limitations in voltage and power posed by the existing semiconductor devices. However, if real power must be delivered to the load, DC-link capacitors exhibit a problematic voltage unbalance, that can be faced in both active or passive ways, that is, by using or not using additional components. Both approaches can be used together, in order to optimize the system performances. The authors have analyzed this problem from an analytical point of view and have developed a modulation control strategy that exploits the inherent redundancy in switching configurations to achieve a correct voltage sharing, in the case of a MPCC with four DC-link capacitors. The results obtained are presented and discussed in a critical way and they are correlated to the case where an active rectifier is used as an input stage to achieve near unity power factor and capacitors voltage balance