基于虚拟同步发电机的MMC受端换流器控制策略

模块化多电平换流器(modular multi-level converter，MMC)的电力电子拓扑结构决定了其零惯性的特性，对系统惯性无支撑作用，系统发生直流传输功率波动和交流系统发生短时功率失衡都可能导致与火电机组相连的交流电网频率产生较大偏差。针对上述问题，提出了一种基于虚拟同步发电机(virtual synchronous generator，VSG)的MMC受端换流器控制策略。该控制策略在MMC功率外环控制中加入一阶惯性环节，为系统提供惯性参数和阻尼参数，使换流器在运行外特性上与同步发电机相类似。通过建立VSG数学模型，对惯性参数和阻尼参数的动态响应进行分析。基于Opal-RT实时仿真，搭建五端MMC-MTDC系统验证所提出的控制策略的正确性与有效性。仿真结果充分表明，当交直流系统功率发生波动时，该控制策略能够在不依靠复杂通信系统的条件下，有效地抑制交流电网频率波动，VSG控制策略能有效为系统提供惯性和阻尼，提高交流系统频率稳定。

Control Strategy of MMC Receiving Converter Based on Virtual Synchronous Generator

The power electronic topological structure of Modular Multi-level Converter (MMC) determines its feature of zero inertia, so it cannot support the system inertia, thus both fluctuation of DC transmitted power and short-time power unbalance in AC system could leads to an evident frequency deviation in AC power grid connected to thermal power generating units. To remedy this defect, a virtual synchronous generator (VSG) based control strategy for receiving converter of MMC was proposed. In this control strategy a first-order damp link was added into the outer-loop control of MMC to provide inertial parameter and damping parameter for the system to make the converter similar to the synchronous generator in external operating characteristic. A mathematical model of VSG was established to analyze the dynamic response of both inertial parameter and damping parameter. Based on Opal-RT real-time simulation, a five-terminal MMC-MTDC system was constructed to verify the correctness and effectiveness of the proposed control strategy. Simulation results show that when the power in AC/DC system fluctuates, the proposed control strategy can effectively suppress the frequency fluctuation in AC power grid without the aid of complex communication system, so it is proved that this control strategy can effectively provide inertial and damping to the system and enhance the frequency stability of AC power grid.