表征柔性直流电网电压动态特性的降阶小扰动稳定模型

The Reduced-order Small-signal Model of VSC-DC Grid to Characterize the Dynamics of DC Voltage

柔性直流技术是提高新能源渗透率,实现“双碳”目标的关键技术之一。低阶、准确的小扰动稳定模型有利于快速分析复杂柔性直流电网电压的超调振荡,为增强柔直系统安全稳定奠定基础。该文以表征直流电压动态特性为目标构建了直流电网降阶小扰动稳定模型。首先,建立直换流站直流侧阻抗模型的二阶解析式,把下垂外环控制参数等效为具有阻感特性的下垂导纳,并将不同控制模式下的柔直换流站以串并联阻抗电路形式统一表达;其次,基于直流网络拓扑聚合形成直流电网降阶传递函数阻抗矩阵,通过对降阶模型进行频率响应分析,定量探究多端柔直换流站通过直流网络耦合对直流电压动态特性产生的交互作用,指导下垂增益、外环控制系数等关键参数的选取;最后,在多场景电磁仿真中验证所述降阶模型的正确性与有效性。

The voltage source converter(VSC)based DC technology is crucial for improving the rate of the penetration of renewable energy resources and achieving carbon peaking and carbon neutrality.Modeling with low order and moderate accuracy is of great significance for fast analysis of DC voltage dynamics and enhancement of system stability.Therefore,the reduced-order model of a VSC-DC grid is built to characterize the dynamics of DC voltage.First,the DC-side impedance of the VSC station is built in the form of second-order expression,which turns the droop-based outer control loop into a specified admittance with resistance-inductance characteristic.The VSC stations with different control are equivalent to a unified model of series-parallel impedance.Next,the reduced-order transfer function matrix of a VSC-DC system is formed based on the grid topology.The interactions of multi-VSC stations on DC voltage dynamics through DC grid coupling are investigated quantitatively by frequency response analysis,thereby guiding the parameters design of the droop gain and the outer control loop.Finally,the correctness and effectiveness of the proposed reduced-order model are validated by simulation.