Positive and negative sequence loop current injection to control internal power imbalance in MMC

MMC is widely used in high-voltage and high-power applications due to its advantages of high modularization, long maintenance interval and low harmonic content of output waveform. Aiming at the internal power imbalance control problem of three-phase symmetrical DC / AC MMC, an internal power imbalance control strategy Firstly, the bridge arm energy and circulation are decomposed into components. According to the mathematical expression of the bridge arm energy, the positive and negative sequence circulation instructions for controlling the power imbalance in the internal phase of the converter are derived. Then, energy conservation of DC side and AC side, the circulating current command for controlling the power imbalance between phases inside the converter is derived. Under the requirement of output current control.By injecting the above circulating current, The optimal input sub-module is determined based on voltage sorting, enabling precise management of the internal power imbalance within DC/AC-MMC systems. Subsequently, simulations are conducted to internal imbalance control strategy, demonstrating its practical applicability.