【作者】 贾俊川；

【导师】 李卫国； 张一工；

【作者基本信息】 华北电力大学（北京） ， 电力系统及其自动化， 2011， 博士

【摘要】 随着能源和环境问题的日益严峻,风力发电作为当今规模化开发程度最高和最具商业化发展前景的可再生能源,已经越来越受到世界各国的关注和重视,近年来得到了大力发展,其中基于变速恒频的双馈风力发电技术因其显著的优势成为风电领域的主流和研究热点。本文针对双馈风力发电系统在理想电网和不对称电网条件下的数学模型、优化控制尤其是双变流器的联合控制策略等方面进行了细致、深入的探讨,主要内容包括：1.推导出三相电压源型PWM变流器在三相静止坐标系和两相同步旋转坐标系中的数学模型,在此基础上,对其稳态特性以及各象限运行区域内桥臂输出电压相量进行了详细的分析、比较,并计算出变流器直流侧电容电压的设定下限值,为双馈风力发电系统的参数选取和变流器控制系统的设计提供了理论依据。提出了同步旋转坐标系中PWM变流器的典型双环控制策略,为双馈风力发电系统中网侧和转子侧变流器的控制研究提供了坚实的理论基础。2.对双馈发电机在不同励磁电流组合方式下的性能以及所需双变流器的容量等方面进行了比较分析,对如何合理利用双变流器的容量和充分发挥其调控能力进行了深入研究,基于双馈发电机的等效电路分析了DFIG在理想电网条件下的功率特性,并在此基础上结合DFIG的损耗特性,提出了双馈风力发电系统新型的无功优化控制策略。该控制策略使部分励磁控制从转子侧变流器转移到网侧变流器,而且使得网侧变流器与转子侧变流器容量相同,给工程实施带来了一系列的便利,如减少了工程备品备件的种类,充分利用了双变流器的无功容量,提高了利用率和运行效率等,具有重要的实际意义。3.推导出电网电压对称故障和不对称故障条件下双馈发电机定子磁链在正、反向同步旋转坐标系中的数学模型,分析了电网故障时DFIG的动态特性,并给出DFIG定子磁链在对称及不对称电压故障情况下的完整解析表达式。通过对持续时间分别为50ms和100ms的两种电压故障的仿真对比分析,指出电网电压对称故障时磁链会以工频振荡,而不对称故障条件下磁链则以两倍工频振荡,且在持续时间为奇数倍工频半周期的故障情况下,电网电压恢复时磁链振荡的幅度是电压跌落时幅值的两倍。分别对各种典型故障情况进行了仿真,结果验证了理论分析的正确性。4.建立了电网电压不对称情况下包括转子侧变流器和网侧变流器的双馈风力发电系统在正、反向同步旋转坐标系中的完整数学模型,并分别推导出定子侧和网侧瞬时有功功率和无功功率的二倍频成分,为双变流器的不对称控制策略的研究提供了理论基础。针对电网电压不对称时双馈系统的运行状态,基于转子侧变流器和网侧变流器分别提出了四种不同的控制策略,并推导出各种控制方案下转子电流和网侧电流负序分量指令值的计算方法。5.详细探讨了电网小数值电压故障情况下双馈系统的穿越控制技术。指出在电网电压对称故障时,可充分发挥并利用双馈发电系统中转子侧变流器和网侧变流器的快速无功调节能力,使对故障期间接入端电压提供支撑,从而削弱故障时机端电压下降的幅度,有助于故障后电网的迅速恢复；在电网电压不对称故障时,提出了不对称电网故障条件下基于双坐标变换的转子侧变流器和网侧变流器的联合控制策略,并设置了不同的性能指标,尽可能地改善双馈系统及电网的整体性能。仿真结果验证了双变流器联合控制策略的有效性。更多还原

【Abstract】 With energy and environment issues increasingly serious, as the current largest scale developmental renewable energy and with the most commercial prospects, wind power has been getting more and more concern and attention by all the countries in the world. In recent years wind power has obtained vigorous expansion, especially doubly-fed wind power system based on variable-speed constant-frequency (VSCF) technology has been one of the main stream models and the control technology of DFIG (Doubly-fed induction generator) wind power generation system has become the research hotspots worldwide due to its excellent advantages. This dissertation aims to discuss the optimal control of wind power and combination control of dual converters in detail based on the mathematical models of doubly-fed wind power generation under symmetric and asymmetric grid conditions. The main contents of this dissertation could be summarized as follows.1. The thesis deduces the precise mathematical models for three-phase voltage-source PWM converter in three-phase stationary reference frame and two-phase rotational reference frame, respectively. Based on the models, PWM converter’s steady state characteristics are analyzed and its different output bridge voltage vectors are compared carefully. DC low limit voltage value of the converter is also calculated, which provides theoretical foundation for selecting doubly-fed wind power system parameters and designing converter control systems properly. The dissertation proposes the typical dual loops control structure of PWM converters in the synchronous rotational reference frame. This will provide the fundamental basis for studying control systems for grid side converter (GSC) and rotor side converter (RSC) further.2. The dissertation makes a comparative analysis of DFIG performances and capacities of the dual converters with several exciting modes, and makes a thorough research for utilizing dual converters capacities properly and bringing their ability of regulation and control into full play. Based on the equivalent circuit of the DFIG, its power characteristics during symmetric grid conditions are obtained. Considering generator losses, a novel reactive power control strategy for doubly-fed wind power system is proposed. This approach reallocates the exciting currents to the stator side and the rotor side. Consequently, the capacity of the GSC is the same as that of the RSC, which makes one converter could be a backup for another. This brings a lot of advantages, such as the less part categories, high usage and operational efficiency, et al. So this method has great practical significance. 3. The stator flux mathematical models in positive- and negative- synchronous reference frames during symmetrical and asymmetrical grid voltage faults are deduced. The dynamic characteristics of the DFIG are analyzed and the complete dynamic-analytical expressions of the stator flux under symmetric and asymmetric voltage fault conditions are provided. Through two typical voltage-fault simulations with the duration of 50ms and 100ms, respectively, this thesis points out that the stator flux will oscillate with the line frequency when the symmetrical gird fault occurs, and with twice the grid frequency under unsymmetrical grid voltage fault condition. Furthermore, under the unsymmetrical grid voltage fault condition with the duration odd multiple half-cycles, when the grid voltage recovers, the amplitude of the flux oscillations can reach twice the oscillating amplitude at the start of voltage sag. Simulations with various typical voltage faults are presented, and the results validate the correctness of the theoretical analysis.4. The dissertation models the doubly-fed wind power generation system, including RSC and GSC, in the positive- and negative- synchronous reference frames under asymmetric grid voltage conditions. The double-line-frequency components of the instantaneous active and reactive powers of the DFIG stator and the AC side of the GSC are analyzed and deduced, which provides a theoretical basis for designing the asymmetric control schemes for the dual converters. Based on the operational states of the doubly-fed wind power system under asymmetric grid voltage conditions, four different control strategies for RSC and GSC are proposed and evaluated, and various negative sequence references of rotor currents and grid side currents within non-identical control scheme are also calculated.5. This dissertation discusses fault ride through (FRT) technology of the DFIG wind power system under slight grid voltage fault conditions in detail. It is concluded that under the symmetrical grid voltage fault, the reactive power rapidly regulated capability of RSC and GSC should be made full use of to support the voltage of point of common coupling (PCC) during voltage fault, which helps to suppress the magnitude of the voltage dropping and helps the network to recover quickly after clearing the gird fault. Under the asymmetrical grid voltage faults, the combination control scheme utilizing rotor side converter and grid side converter based on double coordinate transformation method is proposed. And also the paper sets up, analyzes and evaluates several various performance indexes comparatively. Simulated results verify the correctness and effectiveness of the proposed combination control schemes for dual converters.更多还原