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为提高模块化多电平高压直流输电系统在电网电压不平衡时的运行能力，提出一种新型不平衡控制策略。该策略在正向同步旋转坐标系下电流比例积分(proportional integral，PI)闭环控制的基础上引入以抑制负序电流、抑制有功波动或抑制无功波动为控制目标的辅助控制器，避免了电压、电流正负序分解和繁琐的指令电流计算。为实现上述3种控制目标，对二阶广义积分器(second order generalized integrator，SOGI)、降阶广义积分器(reduced order generalized integrator，ROGI)和降阶矢量比例积分器(reduced order vector proportional integrator，ROVPI)这3种控制器进行了研究对比。研究发现，SOGI作为辅助控制器将产生3次正序谐波，导致电流畸变；与 ROGI 相比，ROVPI 具有更好的控制精度和相位裕度，因此选择ROVPI作为辅助控制器。仿真结果验证所提不平衡控制策略的正确性和有效性。“,”A novel unbalanced control strategy was presented so as to improve operation performances of high voltage direct current transmission based on modular multilevel converter (MMC-HVDC) under unbalanced grid voltages. On the basis of the current proportional integral (PI) closed-loop control method in the positive synchronous reference frame, the novel control strategy developed an auxiliary controller aiming to suppress negative currents, active power fluctuation or reactive power fluctuation, which avoided the decomposition of the positive and negative sequences of currents and voltages and complicated calculation of the reference current. In order to achieve the above control targets, the second order generalized integrator (SOGI), the reduced order generalized integrator (ROGI) and the reduced order vector proportional integrator (ROVPI) were researched and compared. Research results show that the SOGI-based auxiliary controller would produce third positive sequence harmonic, resulting in the current distortion, and ROVPI has better control precision and phase margin than ROGI. Therefore, ROVPI should be selected as the auxiliary controller. Simulation results validate the correctness and effectiveness of the proposed unbalanced control strategy.