Modulation Methods for Balancing the Capacitor Voltages of N-Level Diode-Clamped Converters

Diode-clamped converters (DCCs) suffer from the inherent capacitor voltage imbalance problem. Most software-based voltage-balancing methods fall into the space vector modulation category and the carrier-based pulsewidth modulation category. Despite their effectiveness for the three-level DCCs, it is not easy to extend them to a general n-level topology. In this article, a new modulation method of a category called good-switching (GS) PWM is proposed for balancing the capacitor voltages. The proposed method requires no parameter-tuning effort and is extremely simple to design even for the n-level topology regardless of the number of phases. It is also potentially applicable to other multilevel converters. The principle, the implementation, and the stability analysis of GS-PWM are elaborated for a generic n-level DCC. A modified GS-PWM scheme and an on-off control scheme are proposed to reduce the switching transitions for further realizing the advantages of the GS-PWM. Particularly, the on-off control can be extended to many other voltage-balancing methods. Simulation and experiments with a five-level DCC validate the proposed methods.

Automated summary

A new modulation method called good-switching (GS) PWM is proposed in this article for balancing capacitor voltages. It is simple to design and can be used for any level of topology, and potentially applicable to other multilevel converters.