基于新型直流牵引供电系统的变下垂控制策略

与传统交流制式牵引供电系统相比，基于模块化多电平换流器的中压直流(medium voltage direct current based on modular multilevel converter, MMC-MVDC)牵引供电系统具有电能品质高、供电距离远以及便于分布式可再生能源系统和储能系统接入等诸多优势。针对传统下垂控制下MMC-MVDC牵引供电系统中存在的输出电压跌落、功率分配不平衡问题，提出一种变下垂控制策略。该方法在传统下垂控制中引入下垂扰动量和电压补偿量，利用一致性算法根据各所输出电流得到下垂扰动量实时动态调节下垂系数实现负载功率在各所之间的均匀分配，同时各所输出电压的平均值稳定在额定值附近且偏移量较小。该策略在保证电能质量的同时提高了牵引变电所容量的利用率，在负荷突变时该系统也能较快地重新达到稳态，具备良好的动态特性。最后，在MATLAB/Simulink中搭建了两牵引变电所模型，将提出的控制策略与传统下垂控制进行对比，仿真结果验证了该策略具备较好均流特性的同时能够基本无差地跟踪输出电压参考值，保证MMC-MVDC牵引供电系统的安全、稳定运行。

Variable Droop Control Strategy of Traction PowerSupply System Based on MMC-MVDCS

Compared with traditional AC traction power supply system, medium voltage DC traction power supply system based on modular multilevel converter(MMC-MVDC)has many advantages such as high power quality, long power supply distance and easy access to distributed renewable energy system and energy storage system. Aiming at the above problems existing in MMC-MVDC traction power supply system, an variable droop control strategy is proposed. In this method, droop disturbance and voltage compensation are introduced into the traditional droop control, and uses consistency algorithm to obtain droop disturbance according to output current of each substation to dynamically adjust droop coefficient in real time to achieve uniform distribution of load power among substations, while the average value of output voltage of each substation is stable near the rated value with small offset.This strategy not only ensures the power quality, but also improves the utilization rate of the capacity of the traction substation. In case of sudden load change, the system can quickly reach the steady state and has good dynamic characteristics. Finally, the model of two traction substation is built in Matlab/Simulink, and the control strategy proposed is compared with the traditional droop control.The simulation results verify that the strategy has good current sharing characteristics and can track the output voltage basically without difference, and it can ensures the safe and stable operation of the MMC-MVDC traction power supply system.