双馈风力发电机组低电压穿越控制策略研究

发布时间：2018-12-20 16:24

【摘要】：随着风电装机容量在电网中的比例逐年增大,为了维护电力系统运行的稳定性和安全性,电网制定了并网风力发电机组不脱网运行的低电压穿越要求。双馈风力发电机简称DFIG,为当今世界研究的主流风力发电机型,相比于其他机型,变频器容量大小相对偏小、风机转速可调节、有功功率与无功功率可实现解耦控制；然而,双馈式风机的定子侧直接连接电网侧,使得风电机组对电网故障非常敏感。本文提出了在电网电压小幅骤降时,通过控制策略来实现双馈风力发电机(DFIG)的低电压穿越能力,首先建立了DFIG在电网电压骤降下的暂态励磁精确模型,并在此基础上考虑桨距角对风机的影响,建立了同时控制转子励磁电压和风机桨距角的DFIG发电机四阶非线性模型。基于反馈精确线性化理论,提出了非线性协调控制策略。仿真结果表明,电网电压小幅骤降时,所提出的控制策略能更有效控制转子电流,保护励磁变频器,抑制暂态过程中风机转速振荡,促进电压恢复,维护电网稳定,提高了风力发电机的运行能力和对电网电压骤降的适应性。针对电压大值跌落,通过加入Crowbar保护电路实现低电压穿越。本文分析了双馈风电机组的暂态短路电流的表达式和Crowbar保护电路电阻值的选取；对电压大幅骤降时投入Crowbar电路后引起直流侧过电压问题,建立了基于反馈线性化理论的网侧变频器非线性控制策略。仿真表明,加入Crowbar电路能很好的抑制电流,实现低电压穿越运行；网侧非线性控制器在电压骤降过程中能很好的抑制直流侧过电压。由于在电网电压深度跌落时,采用Crowbar电路,DFIG以异步电机方式运行,将从电网吸收大量无功功率。针对Crowbar电路引起的无功补偿问题,本文考虑协调STATCOM补偿装置,提供动态无功电流用以保证电力系统的稳定性,防止电压进一步下降及Crowbar电路再次动作。通过仿真研究证明了：对引入了Crowbar保护的风机,协调STATCOM能解决无功补偿问题,改善并网电能质量,提高风电机组低电压穿越能力。
[Abstract]:With the proportion of wind power installed capacity increasing year by year, in order to maintain the stability and security of power system, the low voltage traversing requirement of grid connected wind turbine is established. Doubly-fed wind turbine (DFIG,) is the mainstream wind turbine in the world. Compared with other types of wind turbine, the capacity of inverter is relatively small, the speed of fan can be adjusted, and the active power and reactive power can be decoupled. However, the stator side of the doubly-fed fan is directly connected to the grid side, which makes the wind turbine very sensitive to the power grid fault. In this paper, the low voltage traversing capability of doubly-fed wind turbine (DFIG) is realized by control strategy when the voltage drop is small. Firstly, the accurate transient excitation model of DFIG under voltage drop is established. On this basis, considering the influence of pitch angle on fan, the fourth order nonlinear model of DFIG generator is established, which can control both rotor excitation voltage and fan pitch angle. Based on the feedback exact linearization theory, a nonlinear coordinated control strategy is proposed. The simulation results show that the proposed control strategy can control the rotor current more effectively, protect the excitation frequency converter, suppress the oscillation of the fan speed during the transient process, promote the voltage recovery, and maintain the stability of the power network. The performance of the wind turbine is improved and the adaptability to the voltage drop of the grid is improved. For voltage drop, low voltage traversing is realized by adding Crowbar protection circuit. In this paper, the expression of transient short-circuit current of doubly-fed wind turbine and the selection of resistance of Crowbar protection circuit are analyzed. A nonlinear control strategy based on feedback linearization theory is established for DC side overvoltage caused by input of Crowbar circuit when voltage plummeted. The simulation results show that adding Crowbar circuit can restrain the current and realize the low voltage traversing operation, and the nonlinear controller on the grid side can restrain the DC side overvoltage in the process of voltage sag. Because of the Crowbar circuit and the asynchronous motor DFIG will absorb a large amount of reactive power from the power grid. To solve the problem of reactive power compensation caused by Crowbar circuit, this paper considers the coordination of STATCOM compensator to provide dynamic reactive current to ensure the stability of power system and to prevent the further drop of voltage and the reoperation of Crowbar circuit. The simulation results show that the coordinated STATCOM can solve the problem of reactive power compensation, improve the quality of grid-connected power and improve the low voltage traversing ability of wind turbine.
【学位授予单位】：广西大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TM315

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