【作者】 李辉；

【导师】 廖勇；

【作者基本信息】 重庆大学 ， 电气工程， 2011， 博士

【摘要】 双馈异步发电机(DFIG)以其优越的运行性能,在大型变速恒频风力发电系统中得到了广泛应用。然而双馈异步风力发电机组定子侧与电网直接相连的结构决定了其对电网扰动尤其是电网故障异常敏感,使得其在应对不平衡电网条件下的运行及实现低电压穿越方面存在较大缺陷。如何进一步提高DFIG系统在电网电压不平衡及电网故障情况下的安全运行能力已成为当前研究的热点问题。目前,已有学者着手新的拓扑结构的研究,以期改善双馈异步风力发电机组在电网不平衡及电网故障条件下的运行性能。受动态电压恢复器的启发而提出的采用串联网侧变换器的新型双馈异步风力发电系统能够实现零电压穿越,具有优良的低电压穿越(LVRT)能力,是一种先进的LVRT技术。但此类研究还处于起步阶段,国内外研究均较少。本文针对采用串联网侧变换器的新型DFIG系统,结合国内外研究的热点问题,对其在电网电压不平衡及电网故障等异常工况下的运行与控制展开了深入研究,论文的主要研究工作包括:1)利用空间矢量法建立了采用串联网侧变换器的DFIG系统的统一数学模型,进而在此模型基础上提出了电网电压正常时适用于该系统的一种稳态控制策略并通过仿真验证了该策略的正确性和有效性。为进一步研究采用串联网侧变换器的DFIG系统在电网异常条件下的运行与控制奠定了基础。2)分析了电网电压不平衡对DFIG机组的影响及采用串联网侧变换器的DFIG系统在电网电压不平衡条件下的运行情况。在此基础上,从抑制电网电压不平衡对DFIG机组影响及有效增强整个DFIG系统运行性能的角度出发,研究和提出了采用串联网侧变换器的DFIG系统在小值不平衡电网电压条件下的3种增强运行能力控制方案。研究结果表明:与现有文献相比,本文所提方案在确保DFIG机组电磁转矩无2倍频脉动及实现电网电压不平衡条件下整个系统或输出有功功率无2倍频波动或输出无功功率无2倍频波动或整个系统无负序电流注入电网等3种不同运行功能的同时,保证了DFIG三相定、转子电流平衡,避免了定、转子绕组产生不均衡发热危及绕组绝缘,极大地改善了DFIG系统在不平衡电网电压条件下的整体运行性能及其所并电网的运行稳定性。3)在分析电网故障下DFIG的定、转子瞬变分量及采用串联网侧变换器的DFIG系统抑制转子过电流机理的基础上,从限制定子磁场暂态直流分量和负序工频分量及减小从风机吸收能量的角度出发,提出了一种适合于该系统的低电压穿越运行控制策略。研究结果表明本文所提低电压穿越控制策略成功实现了DFIG系统的零电压穿越,有利于提高大型并网双馈风力发电系统的电网故障适应能力,增强其低电压穿越运行性能及提高其所并电网的运行稳定性。4)从电路的角度,解释了电网故障下DFIG转子过电流的原因。针对active Crowbar结构,给出了其Crowbar电阻的确定原则,然后结合仿真,对比分析了几种常用的适用于DFIG系统的低电压穿越方案在电网发生严重对称及非对称短路故障时的技术性能,并进一步探讨了各种低电压穿越方案的经济性。上述工作为工程实现各种低电压穿越方案奠定了一定基础。5)以高性能数字信号处理器(DSP)-TMS320F2812和集成智能功率模块(IPM)为核心,建立了采用串联网侧变换器的DFIG实验系统。分别在电网电压正常及不平衡条件下,对并网运行的采用串联网侧变换器的DFIG系统进行了全面深入的实验研究,以实验结果进一步验证了前述相关分析和研究的正确性和有效性。更多还原

【Abstract】 Doubly fed induction generators (DFIGs) have been widely used for large-scale variable-speed constant-frequency wind power generation systems due to their excellent operational performance. However, as the DFIG’s stator is directly connected to the grid, wind turbines based on the DFIG are very sensitive to grid disturbances, especially to grid faults, and have aggravated operational performance under unbalanced grid voltage condition as well as poor low voltage ride-through (LVRT) capability during grid faults. How to improve the capabilities of the DFIG systems under such abnormal operating conditions has attracted special attention during the last few years. Recently, some research efforts have been devoted to overcome these issues with modified DFIG system topologies. A new DFIG system configuration with an additional grid-side converter, referred to as the series grid-side converter (SGSC), in series with the stator windings of the DFIG and grid connection is proposed where the inspiration for the SGSC is derived from the dynamic voltage restorer (DVR). This topology has been demonstrated to be an advanced low voltage ride-through technology because the DFIG system with this configuration can achieve zero voltage ride-through and has excellent LVRT potential. However, the research on this new topology is still in its early days and there has been little published literature worldwide. This dissertation intends to study the operation and control strategy of the new DFIG system with SGSC under abnormal operating conditions, such as grid voltage unbalance and grid faults. Concrete research work is as follows:1) The unified mathematical model of the DFIG system with SGSC is built by means of space-vector method. Based on this model, a steady-state control strategy suitable for this new topology during normal grid condition is further proposed and verified by simulation results. These works lay the foundation for the operation and control of the DFIG system with SGSC under abnormal operating conditions.2) The impact of grid voltage unbalance on the DFIG and the behaviors of the DFIG system with SGSC under unbalanced grid voltage conditions are analyzed. On this basis, three selective enhanced control strategies are proposed during network unbalance to restrain the adverse effects of voltage unbalance on the DFIG and improve the operational performance of the whole system. Research results show that compared with the existing unbalanced control methods, the main advantage of the proposed method is that while achieving the goals of zero oscillations in electromagnetic torque and total active or reactive power, or total current unbalance, the stator and rotor currents in the three phase windings are also balanced. Thus, the sustained localized heating on the stator and rotor windings caused by the unbalanced stator and rotor currents can be avoided and the life spans of the windings insulation materials would be extended effectively. The operational performance of the whole DFIG system and the stability of the connected grid can also be dramatically improved.3) Based on the analysis of the transient components in the stator and rotor during grid faults and the mechanism for the DFIG system with SGSC suppressing the rotor over current, a LVRT control strategy allowing DFIG to ride through the grid faults is proposed. By controlling the output voltage of SGSC to suppress the transient DC flux and negative sequence flux components in the stator flux and also by controlling the rotor-side converter (RSC) to further restrain the stator and rotor currents, a successful ride-through during grid faults is achieved. Research results show that the proposed control strategy can make the DFIG system with SGSC achieve zero voltage ride-through and improve the LVRT performance of the whole DFIG system and the stability of the connected grid.4) The reason for rotor over current during grid faults is explained from the perspective of electrical circuit. The criterion for determining the value of active Crowbar resistor is given. Then the characteristics of some common LVRT techniques are further researched and analyzed based on the simulation results under severe symmetrical and asymmetrical grid faults. Finally, the economies of these LVRT techniques are discussed. These works lay a certain foundation for engineering development of these LVRT techniques.5) An experimental platform of the DFIG system with SGSC is developed based on the TMS320F2812 digital signal processings (DSPs) and the intelligent power modules (IPMs). On the experimental platform, detailed experiments are carried out during normal and unbalanced grid voltage conditions, respectively. These experimental results further verify the validity and efficiency of the aforementioned analysis and research.更多还原