Single-Stage MMC for Single-Phase AC–DC Applications Using Anti-Series Half-Bridge Submodules with Ultra-Low Capacitance

In this paper, a self-balancing single-stage modular multilevel converter (MMC) is proposed for medium-voltage AC to low-voltage DC applications. The proposed structure utilizes a novel type of submodule which consists of two half-bridges connected in an anti-series arrangement. The proposed converter features minimized stored energy requirements. This is a consequence of (i) operating the converter in such a way that the submodule capacitor voltages naturally follow the AC network voltage, and (ii) that the twice line-frequency power pulsations from the AC network are buffered by the low-voltage DC network. Additionally, the converter employs an interleaved structure that facilitates the natural circulation of switching harmonics within the converter, which reduces the AC network filtering requirements. The topology exhibits operational similarities to the dual active bridge (DAB) converter used in DC-DC applications, and as a result, it requires a control of relatively low-complexity. This paper introduces the proposed topology and its operating principles. Experimental results from a laboratory-scale prototype are provided for 273 Vrms to 150Vdc and 1.3kW.