A Power Balancing Control for Large Power Unbalance in a Modular Multilevel Multiport Converter with Phase-Disposition PWM

A large-scale multiport converter based on the modular multilevel converter (MMC) architecture for charging electric vehicles (EVs) can reduce the volume and installation costs compared to those of conventional multiport converters. It has been pointed out that the multiport converter requires additional circulating current (intra-arm balancing current) to ensure both a balanced grid current and power distribution to the cells under large power unbalance among the cells in one arm. However, a control strategy of the intra-arm balancing current has not been discussed enough in the past. This paper proposes an online minimization control of the intra-arm balancing current. The proposed controller minimizes the intra-arm balancing current with capacitor voltage feedback and a PI controller. In addition, an adaptive observer is installed to adjust the controller gain, which realizes a fast response and stability under all loaded conditions. Experi-mental results verify that the proposed controller ensures a grid current with low total harmonic distortion of 3.1% and capacitor voltage balancing with minimum intra-arm balancing current exhibiting an error of 4.5% from the theoretical value under the largest power unbalance of 1 p.u. among the cells.