Compensation Capability of Intra-Arm Balancing Control for a Multiport Converter based on Modular Multilevel Topology

Abstract

Abstract Multiport converters can be achieved from the modular multilevel converter (MMC) configuration by integrating generation units or loads at the cell level. This can offer advantages in applications such as photovoltaic panels and battery storage units where the loads or generation units have a modular structure. However, this multiport configuration requires an active power balancing of the cells both between arms (inter-arm balancing) and within the arms (intra-arm balancing). It has been pointed out that the intra-arm balancing controller has a compensation limit for the power unbalance. This paper introduces an evaluation functional for quantifying the compensation capabilities of intra-arm balancing controllers in a multiport converter controlled with phase shifted modulation. Two intra-arm balancing control strategies with extended compensation capabilities are developed by maximizing this proposed evaluation functional. The first strategy uses either the dc or grid-frequency component to modify the cell ac voltage depending on the operating conditions. The second proposed method adds also higher harmonic components to the cell ac voltage to further improve the balancing performance. A theoretical evaluation and numerical analysis indicate that the two proposed controllers offer compensation In addition, experimental results confirm the validity of the proposed controllers.