柔性直流输电系统高频稳定性分析及抑制策略(二):阻尼控制抑制策略

High Frequency Stability Analysis and Suppression Strategy of MMC-HVDC Systems(Part Ⅱ): Damping Control Suppression Strategy

柔性直流输电系统高频振荡容易在交流系统阻抗呈现电容效应的频率范围内发生。首先,针对柔性直流换流站详细模型存在阶数很高的问题,在忽略外环、环流抑制控制器(circulating current suppression controller,CCSC)、电容电压等较小影响环节的基础上,建立换流站的简化模型,分析简化模型与详细模型阻抗特性的误差及其适应频率范围;其次,为抑制系统的高频振荡,从控制系统电压前馈和虚拟串联阻抗有源阻尼控制2个方面开展换流站高频阻尼特性提升方案研究,提出采用取整函数的非线性电压前馈策略;再次,以抑制高频振荡和不引起额外频段振荡为约束条件,基于换流站简化模型,解析有源控制器关键参数选择表达式,研究关键参数对换流站阻抗的影响;最后,采用电磁暂态仿真,从高频振荡抑制、电压前馈环节、暂态穿越特性等方面验证所提高频性能提升方案的正确性和有效性。

The high frequency resonance of MMC-HVDC occurs in the frequency ranges where the impedance of the AC system presents capacitance characteristics. Firstly, in view of the problem that the order of detailed model of MMC is too high, the simplified model of which should be established on the basis of neglecting the small influence parts such as the outer loop, circulating current suppression controller(CCSC), capacitor voltage, etc. Firstly, the errors and applicable frequency ranges of simplified model and detailed model were analyzed. Secondly, to suppress the high frequency resonance, the improving scheme of high frequency damping performance of MMC was studied from two aspects of control system. The first one was the nonlinear voltage feed forward method with round function, and the second one was the virtual series impedance active damping control. At the same time, based on the constraint conditions of restraining high frequency resonance and in order not to cause extra frequency resonance, the selection range of key parameters of active damping controller was presented according to the simplified model of MMC, and the influence of key parameters on impedance characteristics was studied. Finally, the electromagnetic transient simulation model was used to verify the correctness and effectiveness of the proposed scheme from the aspects of high frequency resonance suppression, voltage feed forward part modification, transient ride through characteristics.