Current source modular multilevel converter for HVDC and FACTS

Abstract

A current source modular multilevel converter (MMC) is proposed for high voltage AC/DC power conversion applications, such as HVDC and FACTS. Current source converters possess the advantage of short-circuit fault tolerance, which is a pivotal feature for grid applications. By partially following the circuit duality transformations, the proposed converter is derived from the well-known voltage source MMC. Inductor-based current source cells are connected in parallel and form a current source arm that can synthesize a desired current waveform. By adding a reduced-energy capacitor in parallel to each current source arm, these arms can be further connected in series, thereby allowing voltage scaling. By using fully controllable switches, the converter is capable of providing full control on its active and reactive power. Protection schemes against open-circuit failures inside the inductor cells are also proposed. Simulation results show the operation of the current source MMC and its capability of DC fault tolerance.