【作者】 王龙；

【导师】 程时杰； 孙海顺；

【作者基本信息】 华中科技大学 ， 电气工程， 2018， 硕士

【摘要】 风能的大规模开发利用已经成为我国能源战略的重要组成部分。但是,风电场通常位于偏远地区,远离大部分电力用户,需要经过很长的输电线路才能连接到电网中。双馈风电场通过串联电容补偿外送是一种增加输电线路功率传输能力的比较经济的方式。然而,使用串联电容补偿可能导致系统存在次同步振荡的潜在风险。如果不加以防范,这种振荡现象可能会对风电场造成严重损害。同时,随着受控电力电子变流器越来越多地应用到电力系统中,受控电力电子变流器在与电力系统中的其他动态子系统相互作用时可能会导致系统不稳定。本文主要工作包括以下三部分:建立了由双馈风电场和串联电容补偿输电线路组成的单机无穷大系统的小信号模型和PSCAD/EMTDC仿真模型。然后利用特征值分析和时域仿真的方法,研究了双馈风电场经串联电容补偿并网系统的次同步振荡特性。分析和仿真结果表明,双馈风电场次同步振荡模态主要受风速、串联电容补偿度和转子侧变流器内环电流控制比例系数的影响。提出了一种在转子回路中模拟虚拟电阻来抑制双馈风电场并网系统次同步振荡的方法。建立了包含转子侧变流器内环控制回路和虚拟电阻控制的双馈风电场并网系统的等效电路模型。通过特征值分析和时域仿真验证了次同步振荡抑制效果。推导了电压源型变流器的输入导纳模型。利用电网阻抗矩阵和变流器导纳矩阵对电压源型变流器与电网间的闭环稳定性进行了分析研究。对电压源型变流器输入导纳矩阵元素的表达式进行了研究,其中包括对内环电流控制回路,外环直流电压控制回路和用于同步的锁相环进行了建模。该方法的主要优点在于其一般性:对任何阻抗对称或不对称电网都可以建模,而电压源型变流器控制系统的修改仅仅意味着找到另一个输入导纳矩阵。更多还原

【Abstract】 In China,large-scale development and utilization of wind energy has become an integral part of national energy strategy.However,Wind farms are frequently located in remote areas,far from the bulk of electric power users,and require long transmission lines to connect to the grid.Series capacitive compensation of doubly-fed induction generator(DFIG)based wind farm is an economical way to increase the power transfer capability of the transmission line connecting the wind farm to the grid.However,a factor hindering the extensive use of series capacitive compensation is the potential risk of sub-synchronous oscillation(SSO).This oscillatory phenomenon may cause severe damage in the wind farm,if not prevented.With controlled power electronic converters are increasingly being used in power systems,a controlled power electronic converter can cause instabilities when interacting with other dynamic subsystems in a power system.The main work includes the following three parts:A small-signal model and PSCAD/EMTDC simulation model of single machine infinite bus system composed of DFIG and series compensation are built,and the SSO characteristics of a DFIG-based wind farm connected to series compensated transmission system are researched by using eigenvalue analysis and time-domain simulation.Analysis and simulation results show that the wind speed,the proportional parameter of the inner loop of the rotor-side converter and series compensation degree exert a significant effect on the sub-synchronous oscillation characteristics of the system.A method that can mitigate sub-synchronous oscillation in the wind farm by emulating a virtual series resistance on the rotor is proposed.The equivalent circuit model of DFIG is obtain,taking into account the structure of inner current control loop in RSC and virtual resistance controller.Both the eigenvalue analysis and time-domain simulation have validated the effectiveness of this damping method.Input admittance expressions for a voltage-source converter(VSC)are derived.Using impedance and admittance matrices the closed-loop stability analysis of the converter-grid interaction are researched.The expressions for the elements of the VSC input-admittance matrices,in which the current control loop,the direct-voltage control loops,and the phase-locked loop(PLL)used for synchronization are modeled.The main benefit of the method lies in its generality: any grid impedance-symmetric or unsymmetric-can be modeled,while a modification of the VSC control system simply implies finding another input-admittance matrix.更多还原