This study introduces a novel method called overlap onset control (OOC) to balance and maintain alternate arm modular multilevel converter (AAC) submodule capacitor voltages at their desired value. OOC performs zero-current switching and controls the timing of AAC commutation to regulate submodule voltages while retaining output voltage quality. The study uses steady-state converter models to develop the mathematical foundations behind the proposed capacitor voltage regulation method and then presents electromagnetic transient simulation results in PSCAD/EMTDC to demonstrate OOC's ability to extend the AAC operating range.
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