柔性直流输电系统高频振荡特性分析及抑制策略研究

Characteristic Analysis of High-frequency Resonance of Flexible High Voltage Direct Current and Research on Its Damping Control Strategy

柔性直流输电系统的链路延时是其固有特性,使柔直高频阻抗呈现"负电阻电感"特性,可能与长交流线路的分布电容相互作用导致高频振荡失稳现象发生。文章首先建立柔直系统和交流线路等效数学模型。其次,考虑模块化多电平换流器(modular multilevel convert,MMC)内部动态特性、锁相环、环流抑制控制器、延时等因素在内,建立MMC在dq坐标系下的阻抗模型,分析相关环节对柔直高频阻抗特性的影响及高频振荡特性。再次,提出高频振荡阻尼控制策略,采用MMC简化模型分析阻尼控制器参数对阻抗高频特性的影响,并设计保持系统稳定的控制器参数。最后,利用电磁暂态仿真模型验证所提策略的有效性及参数设计的正确性。

Time delay is the inherent feature of MMC-based HVDC transmission system which makes the output impedance of MMC presented"negative resistance and inductance"characteristics in high frequency ranges.Those characteristics may easily cause high-frequency resonant instability interacting with the capacitance feature of long AC lines.Firstly,the equivalent model of MMC and AC lines were derived.Secondly,the impedance model of MMC under dq coordinate was established considering the factors such as internal dynamic processes of MMC,PLL,circulating current suppression controller,time delay,etc.Thirdly,the effect of corresponding factors on impedance matrix in high-frequency ranges as well as resonant characteristics was analyzed.Fourthly,a damping control strategy was proposed to suppress the high-frequency resonant instability.Parameters of damping controller to keep the system stable operation have been designed carefully using the simplified MMC model.Finally,the validity of the proposed strategy and the correctness of the parameters designing were proofed by the electromagnetic transient simulation model.