Suppression Strategy of Circulating Current in MMC-HVDC Based on Quasi-PR controller

The bridge arm circulating current of modular multilevel converter (MMC) based on high-voltage direct current (HVDC) will increase because of its topological structure, which results in system loss increase and system performance degradation. For suppressing the harmonic contents of 2nd, a circulating current suppression strategy in MMC-HVDC based on quasi-PR controller is proposed, which dynamically adjusts the parameters of PR controller according to the power variation, and adopts proportional negative feedback of bridge arm current to suppress circulating current. This strategy does not require phase-to-phase decoupling and double-frequency negative sequence coordinate transformation. Only one quasi-PR controller is used for each phase to suppress bridge arm circulating current in MMC-HVDC, reducing the number of quasi-PR controllers and reducing the complexity of system design. As a result, it greatly reduces the number of use of the quasi-PR controller and the complexity of the system. The simulation and experimental results show that the proposed strategy can effectively suppress the bridge arm circulating current.