【作者】 宋战锋；

【导师】 夏长亮；

【作者基本信息】 天津大学 ， 电机与电器， 2009， 博士

【摘要】 变速恒频双馈风力发电系统的电机结构与绕线式异步电机类似,转子经双向功率变换器与电网连接,流过转子电路的功率为转差功率,降低了变频器成本,通过改变双向功率变换器电子器件导通角调节转子电流的幅值、相位和频率可实现有功和无功输出的灵活控制,对电网可起到无功补偿作用,在商业化机组中应用广泛。本文结合风力发电技术的研究现状以及风力发电产业的大规模发展需求,立题对低电压故障下双馈风力发电系统运行特性与控制策略开展深入研究。本文提出了计及定子磁链变化、励磁电流过渡过程的双馈风力发电系统精确控制模型,为电网故障下双馈风力发电系统特性分析和运行控制提供了理论依据;以此为基础提出了基于自抗扰控制理论的强励控制方案,观测电网扰动及交叉耦合项加以前馈补偿,并利用配置非线性结构代替线性加权和形式,构成非线性误差反馈控制率,在实现解耦控制的同时抑制电网扰动对转子电流的影响,获得了比传统控制方案更优越的不间断运行能力,在系统建模及故障下控制方面具有创新性;在此基础上,本文提出了基于模型补偿ESO理论的双馈风力发电系统转速闭环辨识方法。将辨识转速作为双馈风力发电系统已知模型的一部分,实现转速辨识过程中已知模型的实时连续校正调节,随着已知模型的不断校正调整,有效缩小系统不确定部分的变化范围,有效降低ESO的观测负担,实现转速辨识的快速收敛,达到较好的辨识效果;同时,从系统不确定部分的ESO观测结果中提取转速辨识误差信息,对其进行反馈校正,辨识转速与系统不确定部分的不断校正调节,从结构上改进了原有的开环估计算法,形成了闭环辨识结构。同时,本文开展了低电压故障下双馈风力发电系统的运行性能评估,阐明了低电压故障下双馈风力发电系统暂态响应特性及定、转子磁链的变化规律;采用时域建模分析方法揭示了磁路饱和与集肤效应对双馈风力发电系统暂态响应的影响作用;通过对双馈风力发电系统状态空间模型进行小干扰稳定分析,研究其特征根的变化特性,进一步印证了磁路饱和与集肤效应对系统暂态运行特性的作用机制。研究结果表明,在电网电压跌落时,主磁路饱和对于系统的暂态响应特性无影响;当故障清除、电网电压恢复时,主磁路可能会产生饱和,但其影响程度有限。此外,主磁路饱和引发的励磁电感Lm减小能够增大双馈电机转子暂态阻尼,增强双馈电机的暂态稳定性,使其远离稳定极限。双馈电机集肤效应能够抑制由外部扰动,包括电网扰动引起的电磁暂态振荡,加速暂态分量的衰减过程,在促进系统恢复稳定方面发挥积极作用;但会增大双馈电机定、转子电流暂态冲击,不利于双馈风力发电系统的安全运行,在控制系统研究、暂态特性分析以及转子保护电路设计时应考虑集肤效应的影响。此外,本文从双馈风力发电系统运行控制及载荷分析的角度,提出了包括风速场、变速风机、传动轴系、电机、变流器在内的整个风力发电系统完整模型,为低电压故障下双馈风力发电系统的运行载荷分析提供了模型基础;通过与FAST输出结果的对比分析验证了所建模型的正确性,对其分析结果的可信度进行了评估;在此基础上,明确地揭示出低电压故障对双馈风力发电系统叶片和塔架的影响,为风力发电系统低电压运行控制策略的研究以及面向电网需求的风力发电系统设计提供了理论参考和依据。更多还原

【Abstract】 Doubly-fed induction generator has recently received much attention as one of preferred technology for wind power generation.The structure of doubly-fed induction generators for wind turbine systems is similar to that of typical asynchronous machines. The rotor is connected to the grid through a bi-directional power converter, which only deals with slip power in double direction. It’s not only characterized by its small cubage、light weight and low cost but also realizes flexible connection of mechanical-electric system.This paper analyses the 5th model of DFIG. Then a new rotor current controller based on active–disturbance-rejection control theory is proposed to improve the dynamic response of the system under grid disturbances. This paper carries out simulation of the controller under normal condition and grid disturbances. The results show that the proposed controller can not only tune system power output precisely in normal condition but also ensure prominent reduction of rotor current ripple in order not to be disconnected, which contributes to power system stability. Moreover, the controller takes on good dynamic performances. Besides, for the implementation of sensorless control of doubly-fed induction geneartors, a speed identification algorithm is introduced on the basis of ESO. By means of the existing structure of ADRC system, speed information is picked up from the observation results of the unknown model in ESO. As demonstrated by simulation results, precise identification of speed is achieved.Moreover, taking into account the main flux saturation and deep-bar effect, this paper concentrates on transient responses and stability of the DFIG system under symmetrical grid faults. With increasing wind power penetration, transient responses of doubly-fed-induction-generator based wind turbines gain attentive focus. Accurate prediction of transient performances of DFIG under grid faults is required with increasing wind power penetration. The present paper illustrates the influences of main flux saturation and of deep-bar effect on behaviors of DFIG during voltage dips respectively, and furthermore, clarifies their roles played in the enhancement of system transient stability. Simulation results using Matlab/Simulink are presented for a 1.5MW DFIG wind turbine system. Theoretical and small-signal analyses are also provided. The analyses proposed contribute greatly to proper selection, design and coordination of protection devices and control strategies as well as stability studies.In addition, this paper illustrates the impact of a grid fault on the mechanical loads of a wind turbine. New grid codes require wind turbines to ride-through grid faults. This poses great challenges for the design of both electrical system and mechanical structure of wind turbines. Grid faults generate transients in the generator electromagnetic torque, which are propagated in the wind turbine, stressing its mechanical components. To study the structural loads of wind turbine under grid fault, a complete model including both mechanical and electrical parts must be constructed. A drawback of wind turbine simulation is that either a simple mechanical components is used with a detailed electrical model, or a simple electrical components with a detailed mechanical model is used, which could not provide a throughout insight on the structural loads caused by sudden disturbances on the grid. In this research, a proper combination of different simulation packages, namely FAST (Fatigue, Aerodynamics, Structures and Turbulence) and Matlab, is used to model the electrical and mechanical aspects of a wind turbine respectively. The effect of a grid fault on the wind turbine flexible structure is assessed for a typical wind turbine. A set of simulations reflecting the structural dynamic response of a wind turbine to a grid fault are presented and analyzed.更多还原