Binary Capacitor Voltage Control-based MMC with a Hybrid Arm Design for Low Nominal DC Voltage Applications

Abstract

The main technical challenge of multilevel converters for low nominal voltage is to abate hardware and control complexity and concomitantly aggrandize DC-AC power- conversion quality and efficiency. In the modular multilevel converter (MMC), the half- or full-bridge sub-modules with the arm inductor can derive various sub-module capacitor voltage control approaches. This paper proposes a new MMC concept utilizing the above MMC’s advantage to address the challenge effectively. The proposed binary capacitor voltage control and circulating current control regulate the sub-module capacitor voltages at the power-of-two reference values and the converterarm voltages at the multilevel reference values through a Lyapunov stability-based cost-function optimization approach exploiting the binary numeral system and the proposed hybrid arm design. Therefore, the proposed MMC improves the DC-AC power conversion quality and efficiency by synthesizing a sinusoidal AC voltage with a significantly large number of voltage levels while extensively reducing hardware and control complexity for low nominal DC voltage applications. A simulation study is presented to demonstrate the steady-state and dynamic performance of the proposed MMC under several conditions.