弱电网下直驱风电机组基于运动方程的次同步频带模态频率和阻尼特性估算与分析

Evaluation and Analysis of Direct-Driven Wind Turbines'Modal Frequency and Damping Characteritics in Sub-Synchronous Range Based on Motion Equation Method When Connected to Weak Power Grid

直驱风电机组因其良好的可靠性在新建风电场中正得到越来越多的应用,尤其是在海上风电场景。随着直驱风电机组并网容量的增加,弱电网下与直驱风电机组相关的新型次同步振荡问题正逐渐被发现。目前,关于直驱风电机组新型次同步振荡问题的研究,应用较为广泛的是基于电路等效的阻抗分析法。实际上,电路等效和力学等效在数学上存在严格的对偶关系。本文即是从电力系统熟悉的力学等效即模态视角来分析直驱风电机组的新型次同步振荡问题,并基于运动方程验证了直驱风电机组在次同步频带下的控制相互作用可等效理解为轴系两质量块模型,以及提出了一种定量估算该等效轴系模型固有次同步模态其模态频率和阻尼特性的方法。分析结果均在MATLAB/Simulink中进行了仿真验证。区别于阻抗分析法,本文为电气工程师提供了从模态角度去认识直驱风电机组新型次同步振荡问题的分析方法。

Due to its good reliability,direct-driven wind turbines(WTs)are increasing used in new wind farms,especially in offshore wind farms.With the increasing use of direct-driven WTs,a new type of sub-synchronous oscillation problems related to direct-driven WTs has occurred when connected to weak AC grid.Several studies have tried to analyze these oscillation problems,but most of them used the impedance method from the circuit equivalent perspective.Actually,the circuit equivalent and mechanical equivalent can be transformed to each other.To understand the sub-synchronous oscillation problems related with direct-driven WTs from the perspective of mechanical equivalent,this paper verifies that the dynamic interactions between the DC-link voltage control loop and the phase-locked loop(PLL)are the same as the two-masses shaft model based on the motion equation method,and proposes a quantitative method to evaluate direct-driven WT's intrinsic mode characteristics in sub-synchronous range.Results are all verified in MATLAB/Simulink.In addition to impedance method,this paper provides another modal perspective to understand sub-synchronous oscillation problems related to direct-driven WTs.