Balanced Conduction Loss Distribution among SMs in Modular Multilevel Converters

Abstract

Due to the parameter mismatch, the unbalanced power loss distribution among SMs in the modular multilevel converter (MMC) can be introduced and further deteriorated by the low-frequency asynchronous switching transients related to no-carrier modulation techniques. The unbalanced thermal stress can reduce the reliability of the MMC and increase the complexity of cooling system design. Nevertheless, an internal balance mechanism exists in the MMC thanks to the capacitor voltage balancing. It contributes to an even conduction loss dissipation among SMs, which is studied and revealed in this paper. Moreover, a computationally light conduction loss estimation method is proposed correspondingly relying on the characteristics of semiconductors and the arm current only. Simulations and experiments are conducted to verify the effectiveness the proposed method.