【作者】 胡家兵；

【导师】 贺益康； Lie Xu；

【作者基本信息】 浙江大学 ， 电机与电器， 2009， 博士

【摘要】 随着风电机组装机容量的日益扩大和并网规范要求的不断提高,促使目前国际风电技术的主要研发动向是从正常电网条件下风电机组的变速恒频运行转向电网故障下的穿越运行,其中最为瞩目的研究内容是：适应电网故障下运行的基于双馈异步发电机(DFIG)风电机组的控制模型和控制策略；电网故障对DFIG风电机组影响和保护对策；电网故障下DFIG风电机组的不间断运行控制策略。更为重要的是目前的故障运行研究已从对称故障向不对称故障范畴延伸,这正是风电领域需要努力工作、做出创新贡献且具有挑战性的新研究方向。本文以与大电网或与分布式输电系统相联的DFIG风力发电机系统(简称DFIG风电机组)在外部电网对称、不对称故障下的不间断运行(穿越运行)与控制为主题,从理论分析、运行仿真和实验验证三个方面全方位地进行了全面、深入、细致的研究,获得了一些同步甚至超前于国际风电技术先进水平的重要结论与自主创新研究成果。1.建立了三相定子静止坐标系、两相静止坐标系和两相任意速旋转坐标系中表达的DFIG励磁用网侧PWM变换器和转子侧PWM变换器的精确数学模型。在此基础上,构建了两相同步速旋转坐标系中包括电网状态、DFIG发电机及网侧、转子侧PWM变换器在内的完整风力发电机系统模型,分析了该系统的瞬时有功、无功功率成分。随后,针对网侧PWM变换器引入了基于电网电压定向的直流环节电压、电流双闭环矢量控制策略,针对转子侧PWM变换器建立了两相同步速旋转坐标系中计及定子电压变化、励磁电流过渡过程的DFIG精确控制模型,进一步又提出了分别基于定子电压定向、定子磁链定向的两种改进矢量控制方案,奠定了DFIG风电机组运行分析和电网电压骤降(跌落)故障下实施有效控制的理论基础。仿真分析验证了所建立的DFIG本体精确模型和改进的两种DFIG风电机组矢量控制策略在较小值电网电压骤降故障下实施控制的有效性。2.重点研究了不平衡电网电压条件下DFIG风电机组的运行性能评估、动态建模与增强不间断运行能力的控制对策设计,包括：评估了电网电压不平衡时所包含的负序电压对DFIG励磁用网侧、转子侧变换器运行影响；采用对称分量法建立了不平衡电网电压条件下包括DFIG发电机、网侧、转子侧变换器在内的完整风力发电机系统正、负序dq轴模型；针对DFIG网侧、转子侧变换器分别提出了不平衡电网电压条件下的增强运行能力控制对策及相应的有功、无功功率与正、负序电流指令算法。3.基于不平衡电网电压条件下包括网侧、转子侧变换器在内的正、负序分量形式DFIG风力发电机组完整数学模型,提出、讨论、验证、评估了适合于不平衡电网电压条件下DFIG风力发电机励磁用网侧、转子侧变换器的四种不同正、负序电流控制方案,即正、反转同步速旋转坐标系中的双d-q、PI控制、正、反转同步速旋转坐标系中的主、辅电流控制、两相静止坐标系中及正转同步速旋转坐标系中的比例-谐振(PR)控制和比例-积分-谐振(PI-R)控制方案,以此实现了所提出的电网电压不平衡条件下网侧、转子侧变换器增强运行能力控制的各个目标。翔实的仿真和严格的实验验证了各种电流控制方案在不平衡电网电压条件下的优良控制性能。4.研究了严重对称电压骤降(跌落)时DFIG风电机组的控制策略和保护方案,优化了转子crowbar的投／切时刻,分析了转子crowbar所用串联耗能电阻大小对交流电网恢复的影响,并在此基础上提出了一种采用串联电阻的crowbar和改进网侧变换器控制的低电压穿越运行方案；基于不对称电网故障时DFIG风电机组运行特性,分析了大值不对称故障下励磁变频器中网侧、转子侧变换器容量对两者协同控制的影响,据此提出了一种计及有限励磁变频器容量的改进DFIG不对称电网故障穿越运行控制新策略,仿真结果验证了其有效性。5.为了验证电网电压不平衡条件下DFIG风电机组增强运行能力控制策略的有效性和实用性,获得有实用价值的创新性关键风电技术成果,设计和研制了一台基于双PWM变换器(网侧和转子侧PWM变换器)的变速恒频双馈风力发电机组实验样机系统,对电网电压不平衡条件下DFIG风电机组网侧、转子侧变换器不同增强控制目标、不同正、负序电流控制方案、网侧、转子侧变换器协同控制策略等分别在几种典型运行工况情况下进行了系统深入的实验研究,获得了相对完整的实验成果,对本论文提出的对称、不对称故障下交流励磁DFIG发电机系统基础理论和关键技术从实践角度进行了有效地验证和进一步创新,实现了理论联系实际的全面研究。更多还原

【Abstract】 As the increased penetration of wind power generations in power system, modern grid codes concerning grid-connected wind turbines are developed. As a result, the steady-state response and variable-speed constant-frequency (VSCF) performance of Doubly Fed Induction Generator-based (DFIG-based) wind turbines under normal grid conditions is well understood and applied. The fault ride-through (FRT) operation and control of the DFIG wind power system when network fault conditions has been the main subject of much recent research and development worldwide. The attractive research subjects are as follows, viz., modeling and control of wind turbine driven DFIG adjusting to network fault operation; impact of grid fault on the DFIG and the associated protection schemes; control strategies for ride-through operation of DFIG generation system during network fault. Among them, the most important is that research on the FRT operation has covered asymmetrical grid faults as well as symmetrical ones, which is a challenging and innovative research subject in the field of global wind power technologies.This dissertation intends to study the enhanced control and the fault ride-through operation of wind farms based on DFIG, connected to either a transmission system or embedded within a distribution system, when the network is faulted either symmetrically or asymmetrically. Comprehensive, thorough and detailed studies with respect to theoretical analysis, simulated operations and experimental verifications, are carried out. Keeping in step with advanced wind power technologies globally, some important conclusions and independent-innovative achievements are made and obtained.1. The precise mathematical model of DFIG’s grid-side converter (GSC) and rotor-side converter (RSC) are created and expressed in the three-phase stator stationary reference frame, two-phase stator stationary reference frame and two-phase rotating reference frame at arbitrary angular speed, respectively. Based on the model, the dissertation presents an integrated system model with network, DFIG, GSC and RSC included in the two-phase synchronous reference frame, and analyzes the system’s instantaneous active and reactive powers. Thereafter, a classical vector control scheme based on grid/stator voltage orientation (GVO/SVO) and composed of dual closed-loops, viz., DC-link voltage control and AC current control loops, for DFIG’s GSC is introduced. While for RSC, a precise control model taking the stator voltage variation transients into account is constructed in the synchronous reference frame, and accordingly two improved vector control schemes are suggested based on stator voltage orientation (SVO) and stator flux orientation (SFO), respectively. Simulated analysis verifies the correctness and effectiveness of the proposed DFIG’s control model and the system’s new vector control schemes under relatively small grid voltage dips. It is clearly shown that the two proposed control model designs are useful tools for DFIG fault studies and can be used to determine the required converter rating and protection device settings.2. Under unbalanced network voltage conditions, evaluation of the DFIG’s operation, dynamic modeling of DFIG’s system and design of enhanced control strategies are emphasized. At first, evaluation of the impact of unbalanced network voltage on the DFIG and associated GSC and RSC are carried out. Secondly, via symmetric-component method, novel unified mathematical d-q models of DFIG, GSC and RSC in the positive and negative synchronously rotating frames under unbalanced grid voltage conditions are deduced. Finally, for GSC and RSC four different enhanced control targets are proposed, respectively. According to the positive and negative sequence active and reactive power orders, associated positive and negative sequence current orders are presented in the positive and negative synchronous reference frames.3. Under unbalanced grid voltage conditions, based on the precise models of entire DFIG system, including GSC and RSC, in terms of positive and negative sequence components, the dissertation proposes, discusses, verifies and evaluates four different control schemes for positive/negative sequence currents of DFIG-used GSC and RSC. The four control schemes are dual d-q PI current controllers implemented in the respective positive and negative synchronous reference frames, main and auxiliary current controllers in the positive and negative synchronous reference frames, proportional resonant (P-R) current controller in the two-phase stator stationary reference frame and proportional integral plus resonant (PI-R) in the positive synchronous reference frame. Once the positive and negative sequence currents are fully regulated, the proposed enhanced control targets for GSC and RSC are completely realized during network unbalance. Detailed simulations and comprehensive experiments verify the feasibility and performance of each current control schemes when the network voltage is unbalanced.4. The dissertation studies control strategies and protection schemes for DFIG wind generation systems under serious grid voltage dip conditions. The timing of rotor crowbar’s switching on and off is optimized. The impact of value of resistor series-connected to rotor crowbar on faulted network recovery is analyzed. On the basis, a FRT operation scheme composed of a series-connected resistor rotor crowbar and an improved grid-side converter control strategy is proposed. Concerning the operation characteristics of wind turbine driven DFIG system during network unbalance, the dissertation analyzes the impact of limited ratings of GSC and RSC on the coordinated control strategies when the network voltage is relatively larger unbalanced. Thereafter, another improved unbalanced FRT control scheme for DFIG system by taking into account the limited converter’s ratings is presented and simulated results are shown to confirm its feasibility.5. In order to verify the effectiveness and practicability of the enhanced control strategies for DFIG wind power generation systems during network voltage unbalance, the dissertation designs and develops a VSCF DFIG test rig based on GSC and RSC. On the test rig, detailed experiments are carried out under a few classical operation conditions when the network voltage is unbalanced. Several practical and independent-innovative achievements on key wind power technologies are obtained, viz., different enhanced control targets for GSC and RSC during network unbalance, various positive/negative sequence current control schemes and coordinated control strategies of GSC and RSC under unbalanced network voltage conditions. The experimental results further confirm the feasibility of the proposed basic theories and key technologies for AC-excited DFIG wind power system under both symmetrical and asymmetrical network fault conditions. As a result, theory and practice are achieved thoroughly.更多还原