A Power De-coupling Control Strategy for MMC-HVDC System

Modular multilevel converter (MMC) has a wide range of applications in the field of HVDC. However, some of the electricity in MMC is coupled, which makes the design of control system more difficult and have a negative impact on the stable operation of the system. This paper puts forward a strategy to eliminate the coupling control, this method compensates the current cross-coupling terms of the d-axis and the q-axis in the dq coordinate system, SOGI(Second Order Generalized Integrator) and Q-PR(Quasi-PR) controller are used to accurately control the double frequency circulation in the internal unbalanced current, the coupling caused by the internal unbalance current and the sub-capacitor module voltage is compensated in the three-phase coordinate system. Finally, the simulation verification is carried out in PSCAD, which is compared with the traditional control method to verify that the proposed method can achieve complete power decoupling.