柔性直流输电稳定性分析及控制参数整定

针对柔性直流输电的特点,将其稳定性分析分为两部分,即柔直系统直流侧稳定性分析和交直流互联的稳定性分析。对于直流侧的稳定性分析,首先建立柔直系统的简化复频域电路,然后得到等效环路增益,采用Middlebrook判据进行稳定性判断;对于柔直系统与交流互联网络,首先探讨其稳定性机理,然后通过dq旋转坐标系下的电流环控制结构框图构建换流站的等效电路,并推导出换流站的等效导纳表达式,最后通过注入非特征谐波电流法进行交流侧阻抗检测,利用交直流阻抗比的频域特性进行稳定性判断,找出稳定的控制参数域。利用PSCAD/EMTDC软件对实际工程中不同等效场景下交流侧阻抗对稳定性的影响进行仿真,证明了采用所提方法进行稳定性判断及控制参数整定的有效性。

VSC-HVDC Stability Analysis and Control Parameter Setting

According to the characteristics of the voltage source converter based high voltage direct current (VSC-HVDC), the paper divides the stability analysis of VSC-HVDC into two parts, namely VSC-HVDC DC side stability analysis and AC-DC interconnected stability analysis. Regarding the DC side stability analysis, the VSC-HVDC simplified circuit in complex-frequency domain is established, and then the equivalent loop gain is obtained, at last Middlebrook criterion judges the stability of VSC-HVDC. For the stability between VSC-HVDC and AC network, its stability principle is firstly discussed, and then the equivalent circuit of VSC is built by the structure diagram of the current loop control in dq reference frame, finally the equivalent admittance expressions of converter station are deduced. Thereafter, the AC impedance is tested through the uncharacteristic harmonics current injection method, while the frequency domain characteristic of AC-DC impedance ratio is used as stability judging criterion to find the stable control parameters domain. The time domain electromagnetic transient simulation in PSCAD/EMTDC shows the impacts of different AC impedances on VSC-HVDC system stability, which verifies the proposed stability criterion analysis and control parameter setting method.