直驱风机直流母线电压控制对系统功率振荡的影响分析及改进方法

Influence of DC Bus Voltage Control of Direct-drive PMSG on Power Oscillation and Its Improvement

近年来,直驱风电场与交流系统相互作用引发功率振荡的问题引起了国内外学者的广泛关注。文章重点关注并网变流器直流母线电压控制环节,提出了一种增强直驱风机并网系统稳定性的改进控制方法。首先建立了传统直流母线电压控制下直驱风机并网系统的阻抗模型,并解析推导了电压外环控制参数对系统稳定性的影响;在此基础上提出了在电压外环控制系统中引入时变系数的改进控制方法。阻抗分析表明,所提方法可以显著增强系统在振荡频段内的稳定性;通过特征值分析和时域仿真对比了传统电压外环控制方法和所提方法下的系统稳定性,证明了所提方法在不同运行条件下均可以有效改善系统稳定性。

Recently,the power oscillations caused by the interaction between direct-drive permanent magnet synchronous generator(PMSG)based wind farms and AC system has aroused wide attention.Focusing on the DC bus voltage control of the grid-connected converter,this paper proposes an improved DC bus voltage control method to enhance the stability of the PMSG grid-connected system.Firstly,the impedance model of the conventional direct-drive PMSG grid-connected system is established,and the influence of voltage outer loop control on the system stability is deduced.Based on this,an improved control method by introducing a time-varying coefficient into the voltage outer loop control system is proposed.The impedance analysis shows that the proposed method can significantly enhance the stability of the system in the oscillating frequency band.Finally,the eigenvalue analysis and the time-domain simulation are used to compare the system stabilities under the traditional method and the proposed method respectively.The results prove that the proposed method can effectively improve the stability of the system under different operating conditions.