【作者】 张学广；

【导师】 徐殿国；

【作者基本信息】 哈尔滨工业大学 ， 电力电子与电力传动， 2010， 博士

【摘要】 随着风力发电规模的迅速发展,风电在电网中的比例越来越大,大型风力发电机组的并网运行控制问题目前得到了广泛的关注。双馈风力发电机组是目前最广泛采用的风电机组类型,由于其自身结构的特点,其大规模的应用会给机组自身控制和电网安全稳定运行带来一系列的问题。为满足未来电网并网规约对风电机组运行的要求,本论文对双馈风电机组的并网运行控制策略进行了研究。研究内容主要包括:建立了双馈发电机在电网同步坐标系下的数学模型,给出了双馈发电机阶段并网控制方法。根据双馈风力发电机运行的特点,针对双馈发电机并网前空载励磁阶段和并网后发电运行阶段分别采用了不同的无速度传感器矢量控制方案。在发电机并网前,根据双馈发电机空载时定子侧电压估计发电机并网前转速及转子位置,在并网运行阶段,采用一种基于双馈电机磁链关系的模型参考自适应方法进行转速及转子位置的跟踪。仿真和实验结果表明了这种方法的有效性。双馈发电机组电网故障情况下的低电压穿越控制问题是本文研究的重点。根据双馈风力发电机内部的电磁关系,分析了理想三相对称短路情况下双馈发电机运行状态对短路电流的影响。在此基础上本文提出了一种基于电网电压矢量定向的双馈发电机灭磁控制策略。研究表明这种方法可以在电网电压跌落程度较小的情况下有效地减小双馈风力发电机定子磁链中直流暂态分量的影响,提高双馈风电系统的稳定性。研究了电网对称故障情况下基于active crowbar的双馈发电机的控制策略。通过crowbar的合理设计和控制,可以实现电网严重对称故障情况下的低电压穿越运行。在风电机组的控制中,电网同步信息的准确获取是对风电机组控制的关键。针对传统的三相电网相角检测方法在电网波动及故障情况下的不足,本文提出了一种新型的数字锁相环设计方法。所提出的锁相环在正序负序双同步坐标系下,采用移相控制器消除电网不平衡电压带来的影响。针对电网频率偏移造成的移相的偏差,采用变周期采样的方法使系统有效的跟踪电网频率的变化。在电网不对称故障情况下,针对双馈发电机采用了正序和负序双同步坐标系下的矢量控制策略,分析了不同控制目标下所需的转子负序电流给定值。针对网侧变换器的控制,本文在传统的PWM整流器矢量控制方法的基础上,改进了正序负序双同步坐标系下的矢量控制方法,这种方法既可以根据不同控制目标对正序负序电流进行单独控制,也可以有效避免采用双同步坐标系可能带来的谐波问题。针对目前广泛采用的LCL滤波器,提出了一种不需添加额外传感器的有源阻尼控制方法,实验结果验证了这种方法的有效性。结合双馈风电机组的运行特点,提出了一种改进的配电网双馈风电场的电压控制策略。其中既包括传统的通过无功功率控制电网电压的方法也包括电网负序电压的补偿控制策略。给出了双馈风电机组不同运行状态下的无功功率的计算方法,阐述了双馈风电机组的无功功率控制方法及通过风电场无功功率控制电网电压的方法。针对电网电压不平衡的情况,给出了通过双馈风电机组抑制电网负序电压影响的控制方法,分析了双馈机组的控制电网负序电压的限制条件和控制策略。研究结果表明这种电压控制方法在风电场配电网连接条件下可以有效地提高风电场及机组运行的稳定性。研制了一套双馈风电机组实验室模拟平台。模拟平台上目前能够实现双馈发电机的无冲击并网运行控制,亚同步到超同步区间的变速恒频运行,发电机的有功无功功率解耦控制以及功率变换器的能量双向流动控制等功能。在实验室模拟平台基础上,以一个实际工程项目为背景研制了一套1.5MW双馈发电机组的功率变换器控制系统,并在试验站完成了部分地面测试。更多还原

【Abstract】 With the development of wind power, the penetration of wind power in power grid increases rapidly. The grid connection operation of wind generator is paid great attention now. Doubly Fed Induction Generator (DFIG) is the most popular wind generator type adopted in the world. Because of its characteristic, the large-scale application of DFIG will bring many problems to the generator safety and power grid stability. In order to satisfy the grid code requirement, the grid connection control strategy of DFIG is researched in this dissertation. The main contents of this dissertation include:The mathematical model of DFIG in the synchronous coordinate system and the DFIG stage-wise control method are introduced. Due to the operation characteristics of DFIG, two close-loop control strategies are adopted respectively to estimate the rotor speed and position based on the generator grid-connect condition. Before the grid connection, the rotor speed and position are estimated through the stator voltage. When the generator is connected to the grid, the model reference adaptive control (MRAC) method based on the electromagnetism relationship of DFIG is used to estimate the rotor speed and position. The control strategy is verified by simulation and experimental results.Low voltage ride through (LVRT) control of DFIG is a significant content in this dissertation. Based on the electromagnetic relationship in DFIG, the principle of DFIG short circuit current is analyzed when three-phase short circuit fault occurred in stator and the influence of generator pre-fault operation state on short current is also analyzed. The active crowbar control method in symmetrical grid fault condition is researched. Simulation results shows that with proper design and control, LVRT of DFIG can be achieved during serious grid fault. In unbalanced grid condition, dual vector control strategy in positive and negative synchronous coordinate frame is adopted. Different negative sequence rotor current references for special control targets are introduced.The transient DC flux component will emerge in DFIG stator because of the voltage change caused by grid fault, which makes the output power fluctuate and the electromagnetic torque vibrate. A novel flux damping control strategy of DFIG based on grid voltage oriented is proposed. Research result shows that the transient DC flux component can be eliminated quickly and the stability of system will be improved, so this method is helpful to achieve the LVRT operation of DFIG system.In grid-connected wind generation systems, the grid information is very important to the control of wind generators and converters. In grid distortion and fault condition, especially in unbalanced condition, the detection of grid synchronization information will be badly disturbed. A novel three phase PLL design method is proposed because of the drawbacks of conventional grid voltage detection method. The influence caused by unbalanced voltage is eliminated by a delayed signal cancellation (DSC) controller in double synchronous reference frame.A variable period sampling method is used to trace the frequency and eliminate phase shift offset which is caused by frequency deviation.Based on the conventional vector control strategy of the grid side converter, an improved positive and negative sequence double synchronous vector control method is proposed. Through this method, both positive and negative sequence current can be controlled respectively and the front-end voltage distortion introduced by double synchronous will be avoided. The LCL filter is widely used in three phase voltage source PWM converter for its good performance. A novel active damping control strategy is proposed and the capacitor current estimate method is adopted so no addition sensor is needed. The feasibility of the proposed method is verified through experimental results.An improved grid voltage control strategy of DFIG wind farm in distribution networks is proposed based on the DFIG operation characteristic. The voltage control methods of reactive power and negative sequence voltage compensation are included. A modified reactive power limit calculation method in different operation states of DFIG is analyzed and the reactive power control strategy is introduced. The negative sequence voltage compensation control strategy of DFIG is proposed for unbalanced grid voltage condition. The compensation limit is given based on the current margins and DC voltage limitation of grid side converter. The distribution algorithms of negative sequence current in the wind farm and in the generator system are also introduced. Research result shown that the stability of wind farm and DFIG ysytem is improved through the grid voltage method.An experimental platform of DFIG wind power generation system is developed. The grid-connection control, VSCF operation between sub-synchronous and super- synchronous, active and reactive power decoupled control and bidirectional operation of converter system are achieved. Based on the experimental platform, a 1.5MW DFIG control system is designed for a project, and the on-ground test is carried out in the test bench.更多还原