直流微电网的稳定性分析及有源阻尼控制研究

直流微电网中恒功率负荷(constant power load,CPL)表现为负阻尼特性,其大量接入会降低系统阻尼,引起直流母线电压振荡失稳。为此,提出一种虚拟电阻控制策略补偿下垂系数来提高系统稳定裕度。基于所提控制方法,建立直流微电网的小信号模型,分析直流侧电容、负荷功率、下垂系数和电流控制器参数变化对系统稳定性的影响,并对各参数进行灵敏度分析;根据下垂系数灵敏度大这一分析结果,提出虚拟电阻控制策略。再者,对于虚拟电阻在不同源变换器的应用效果,分别从Nyquist曲线图和灵敏度进行定性、定量分析,得出所提控制策略应用到网侧变换器对系统稳定性的提高效果更好。最后,在Matlab/Simulink中建立直流微电网模型进行仿真,仿真结果表明,所提控制策略能有效增强系统阻尼,提高系统稳定性。

Stability Analysis and Research of Active Damping Control Method for DC Microgrids

Owing to the negative damping characteristic of constant power load(CPL)in DC microgrid,the DC bus voltage is prone to oscillation and even instability with the large number of CPL access.Therefore,a virtual resistance control strategy is adopted to improve the stability margin of the system by compensating the droop coefficient.Based on the proposed control strategy,a small-signal model of the DC microgrid is derived.The influences of changing parameters,such as DC bus capacitance,load power,droop coefficient and current-loop controller parameters,on system stability are analyzed and the sensitivity of each parameter is calculated.Based on the high sensitivity of the droop coefficient,the virtual resistance control strategy is proposed.Then,qualitative analysis from Nyquist curve and quantitative analysis from sensitivity are conducted to compare the application effect of virtual resistance in different source converters,which shows that the proposed control strategy has a better improvement in the system stability when applied to the grid-side converter.Finally,a DC microgrid model is built and simulated in Matlab/Simulink.Simulation results show that the strategy can effectively enhance damping and improve stability of DC microgrid.