网压不平衡下柔直换流端能量平衡研究

基于模块化多电平换流器(Modular Multilevel Converter, MMC)的柔性直流输电系统近年来受到广泛的关注。针对电网电压不平衡下MMC运行情况进行研究,提出了一种能量均衡控制策略,以改善模块化多电平变换器在不平衡网压条件下的换流器内部能量平衡。该策略通过分析桥臂能量与各电气信号耦合关系,在0■β坐标系下建立桥臂能量数学模型,前馈补偿的加入提高了MMC在交流电网不对称故障和突发电压不平衡情况下的抗干扰能力。通过优化换流器内部电流分量进行桥臂能量平衡控制,实现网压不平衡下交流侧电流与换流器内部能量协同控制。最后,通过Matlab/Simulink平台搭建了双端MMC仿真模型。仿真结果验证了所提出控制策略的有效性。

Research on energy balance of a flexible and direct converter terminal under unbalanced grid voltage

The flexible HVDC transmission system based on a Modular Multilevel Converter (MMC) has attracted a lot of attention in recent years. The operation of an MMC under unbalanced grid voltage is studied, and an energy balance control strategy is proposed to improve the internal energy balance of the MMC under unbalanced grid conditions. By analyzing the coupling relationship between the bridge arm energy and electrical signals, a mathematical model of bridge arm energy is established in a coordinate system, and the anti-interference ability of the AC network under asymmetric faults and uneven burst voltage is improved by adding feed-forward compensation. The energy balance control of the bridge arm is carried out by optimizing the internal current component of the converter. This realizes coordinated control of AC side current and internal energy of the converter under an unbalanced network voltage. Finally, a two-terminal MMC simulation model is built on the platform of Matlab/Simulink. The simulation results verify the effectiveness of the proposed control strategy. This work is supported by National Natural Science Foundation of China (No. 51977014) and Science and Technology Project of Hunan Province (No. 2018KJ151).