Intra-arm Balancing Control of Cascaded Multi-Port Converter for Whole Power Unbalance Conditions

This paper proposes a capacitor voltage balancing control for load imbalance among cells in a cascaded multi-port converter. The input/output power of the cell is controlled by adjusting the ac-side voltage of the cell to balance the capacitor voltage even when the load imbalance occurs in the arm. The current of the multi-port converter with the conventional controller can distort due to overmodulation of the cell under the large load imbalance. The proposed controller prevents overmodulation with the improved generation method of the ac-side voltage, which extends the operation region with respect to the power imbalance. Furthermore, the proposed controller injects minimal additional circulating current to achieve the operation for whole power conditions. The experimental results reveal that the proposed controller improves the total harmonic distortion of the grid current by 2.9p.t. with minimal circulating current while achieving the capacitor voltage balancing.