Zero‐Current Switching Based Model Predictive Control of a Double‐Extended Overlapped Alternate Arm Converter Used in the VSC–HVDC System

ABSTRACT The alternate arm converter (AAC) is one of the most efficient multilevel topologies based on voltage source converters (VSCs), which has recently gained attention in various applications, particularly in high voltage direct current (HVDC) systems. Given that the AAC operates in both overlap and non‐overlap modes, the proposed controller must be capable of controlling the AC‐side output currents while minimising harmonic distortion in both modes. Moreover, during overlap operation, circulating currents within the AAC phases lead to excess energy accumulation in the arms, necessitating the regulation of these current components. This paper employs full‐bridge AAC structures at both terminals of a VSC–HVDC system. To model the AAC converter and design its control system, the average model is utilised, while control of AC currents, circulating currents, and voltage balancing is achieved through zero‐current switching‐based model predictive control. The introduction of the ‘double‐overlap’ concept ensures zero‐current switching of the director switches. This control strategy allows the extension of the overlap period beyond its marginal value without increasing the number of submodules. Simulation results and comparative studies demonstrate the superior performance of the proposed controller.