交直流配电网小信号模型和直流侧低频振荡分析

交直流配电网发展迅猛、应用广泛,其稳定性是行业关注的焦点。文中针对某交直流配电网工程调试阶段出现的直流侧低频振荡现象,开展稳定性分析。文中首先在小信号建模基础上,采用特征值分析方法,分析电网强度、功率水平、控制参数3种因素对低频振荡的影响。随后,文中提出改变控制器参数和增加附加控制器的振荡抑制措施。理论和仿真分析表明:弱电网会影响电压源型变换器(VSC)的稳定性;375 V直流侧功率增大至超过额定功率时会发生低频振荡;Buck变换器电流内环比例积分(PI)控制器积分系数不影响系统的稳定性,但影响振荡发生后的振荡频率,电压外环PI控制器比例系数过小或积分系数过大会造成系统不稳定;改变Buck变换器电压外环PI控制器参数和增加附加控制器可有效抑制低频振荡。文中针对实际交直流配电网振荡影响因素的理论及仿真分析,对其他交直流配电网工程调试及运行分析具有借鉴意义。

Small signal model and DC side low frequency oscillation analysis of AC/DC distribution network

With the rapid development and wide range application of AC/DC distribution network,its stability has also become the focus. The low-frequency oscillation at the DC side in the commissioning stage of an AC/DC distribution network project is analyzed. Based on the small signal modeling,the eigenvalue analysis method is used to analyze the influence laws of short circuit ratio (SCR),power level and control parameters on low-frequency oscillation. Next,the measures of changing controller parameters and adding additional controllers to suppress oscillation are proposed. The theoretical analysis and simulation test show that weak grid affects the stability of voltage source converter (VSC). Low frequency oscillation occurs when the 375 V DC side power increases to exceed the rated power. The integral coefficient of the Buck converter current inner loop proportional integral (PI) controller does not affect the stability of the system,but it affects the oscillation frequency after the oscillation occurs. If the proportional coefficient of the voltage outer loop PI controller is too small or the integral coefficient is too large,the system is unstable. Changing voltage outer loop PI controller parameters of Buck converter and adding additional controller can effectively suppress low-frequency oscillations. The theory and simulation analysis of the actual AC/DC distribution network oscillation influence factors are of reference significance for the commissioning and operation analysis of other AC/DC distribution network projects.