An Improved Circulating Current Suppression Strategy Based on Quasi-PR Controller for MMC-HVDC System

Circulating current flowing in the internal electrical system of Modular Multilevel Converter (MMC) bridge arm is a common phenomenon when system operates normally. This current will lead to active power loss and cost increase. To solve the problem, an improved control strategy is proposed in this paper to reduce the current circulation in MMC system based on quasi-PR controller. This control strategy neither requires additional controller nor complicated control parameters. For the purpose of showing the validity of the controller, this paper employs PSCAD/EMTDC simulation platform establishing the model of electrical circuit and controller and analyses the simulation result. From the simulation results, it is obvious that the improved strategy has the capacitance of significantly inhibiting the bridge arm current circulation and has well performance.