基于MMC的海上风电场柔性直流输电变流器仿真

Simulation of MMC-based converter for flexible direct current transmission of offshore wind farm

针对海上风电场柔性直流输电变流器所采用的拓扑结构及控制方式进行了详细研究,主电路采用一种新型模块化级联多电平变流器结构,建立该结构的等效数学模型;根据变流器各相桥臂子模块电容电压对其进行排序,再结合桥臂电流方向及排序结果确定各模块状态,从而保证同一桥臂内各模块电容电压瞬时值相等;控制系统采用双闭环矢量控制方式,两端变流器互相协调,风场侧控制直流电压,电网侧控制有功功率;同时,内环采用电流前馈解耦方式,分别独立控制有功功率、无功功率。利用Matlab搭建整个系统的仿真模型,验证了所采用拓扑结构的优越性以及控制方式的正确性。

The topological structure and control strategy of converter for the flexible direct current transmission of off-shore wind farm are studied.The structure of MMC（Modular Multilevel Converter） is adopted as its main circuit and its equivalent mathematical model is established.The sub-modules of each bridge arm are sorted according to their capacitor voltages,which,combined with the arm current direction,determines the states of sub-modules to ensure that the instantaneous capacitor voltage of every sub-module is equal within the same arm.Dual close-loop vector control strategy is applied：the converter at wind farm side controls DC voltage while the converter at grid side controls active power.The inner loop adopts the current feed-forward decoupled mode to control the active power and reactive power independently.The simulation system model is set in Matlab and the advantage of adopted topological structure and the correctness of applied control strategy are verified.