Submodule Voltage Balancing and Loss Equalisation in Alternate Arm Converters Based on Virtual Voltages

摘要

Balancing of the submodule (SM) capacitor voltages in the alternate arm converter (AAC) exhibits a great amount of similarities with other modular topologies, especially the modular multilevel converter (MMC). However, the requirements of operation at overmodulation range and the alternate conduction of the phase current further complicate the voltage balancing task. In this paper, a voltage balancing and loss equalisation approach based on virtual SM voltages in combination with sorting algorithms is introduced. The developed approach uses the switching states of the SMs as feedback and provides reduction of the switching frequency of the SMs, further addressing excessive switching due to component parameter variation, tolerances and faults. The effectiveness of the algorithm is demonstrated with simulation results from an equivalent full switching model of an AAC for HVDC applications.