【作者】 李珊瑚；

【导师】 杜雄；

【作者基本信息】 重庆大学 ， 电气工程， 2011， 硕士

【摘要】 随着风电场的规模和风机单机容量越来越大,风电接入后对电网运行的影响也日益突出。电网规程要求风电机组具有电网故障穿越能力。直驱型风电机组通过全功率变流装置接入电网,一般认为全功率变换器将电网和发电机组解耦,对电网波动的适应性好,相比双馈结构更易穿越电网故障,具有较好的应用前景。直驱风电机组在电网故障下运行仍然会产生很多问题,特别是在不对称故障情况下,存在较多问题亟待解决。并网变流器同步信号的提取是直驱风电机组并网稳定运行的前提,本文将对准确提取电网同步信号的方法,以及直驱风电机组的故障穿越控制策略开展研究工作。在电网电压不对称和含有谐波的情况下,直驱风电机组中网侧换流器的控制需要提取电网电压的同步信号,并实现正负序分离。在电网电压畸变的情况下,现有提取同步信号和正负序分量的方法都受到谐波的干扰,本文提出一种基于解耦多同步参考坐标系的同步信号检测方法(DMRSF-PLL),该方法通过在正负序dq轴系以及低次谐波的dq轴系分解,实现了多轴系dq分量的解耦,可以在电网电压不对称和含有谐波分量的情况下,快速提取出电网电压的频率和相位信息,同时还可得到正负序分量的dq轴变换结果。仿真结果表明提出的方法在电网电压不对称、频率变化和含有多次谐波情况下均具有很好的同步效果。将该方法应用到直驱风电机组并网系统中进行仿真验证,仿真结果表明该方法能消除电网电压谐波对输出电流的影响。根据电网故障特征,本论文首先分析了直驱风电机组(以永磁同步发电机组PMSG为参考)在故障运行条件下的功率关系,根据分析结果将电网故障情况下机组实现故障穿越所面临的问题总结为由电网电压正序分量有效值下降带来的“有功不平衡”和电网电压负序分量带来的“功率波动”两类问题。依据所总结的这两类问题,对目前直驱风力发电机组的故障穿越方法进行了总结,分析了不同方法的优缺点,提出了直驱风力发电系统的故障穿越控制仍然需要研究解决的问题。根据直驱风电机组在不对称故障情况下产生的网侧负序电流和直流母线电压波动的问题,本文提出了一种PMSG机组的控制策略,该控制策略可消除网侧变换器并网电流的负序分量和抑制直流母线电容电压的二倍工频波动。在网侧换流器的控制中采用电网负序电压前馈的方法来消除并网电流负序分量;在机侧变换器的控制中提出了一种新的发电机电磁功率跟踪控制思想,使发电机的输出功率跟踪网侧变换器的输出功率,抑制了不对称故障情况下直流母线电压的二倍工频纹波和限制直流侧电压上升,提高了不对称故障穿越能力。通过仿真分析,验证了故障各种工况下文中提出的控制方法的有效性。本文设计了数字控制三相并网变换器实验样机,给出了其软硬件的详细设计过程。利用该样机,对DMSRF_PLL方法进行实验验证,实验结果表明提出的方法在电网电压不对称、频率变化和含有多次谐波情况下均具有很好的同步效果。在稳态工作情况下进行三相并网变换器实验研究,并给出了实验结果。更多还原

【Abstract】 Along with the enlargement of capacity of wind turbine and the scale of wind farm, the influence of wind power integration on the operation of power grid is increasingly outstanding. The wind turbine is required to meet with grid code to achieve fault ride-through under grid fault condition. Compared with doubly-fed system, direct drive wind turbine which integrates to power grid by using full power converter which is generally thought to decouple the grid and generator set is easier to achieve fault ride-through, thus having a good prospect of application. However, The wind turbine will face a series challenge under grid fault condition, especially under unbalanced grid conditions. The extraction of the synchronous signal of grid-connected power conversion is the precondition for a stable operation. Thus, this paper makes research on methods of extracting grid voltage synchronization signal and the control strategy of fault ride-through control for direct-drive wind turbine, is also studied.The control of grid-side converter of the direct-driven wind power turbine needs to extract the grid voltage synchronization signal and to achieve positive and negative sequence separation under asymmetrical grid voltage and harmonics conditions. The existing ways of extracting synchronous signal and positive and negative sequence are subjected to harmonic interference. Due to the limited performance of frequency detection and fundamental component separation of the existing grid voltage synchronization method under harmonic condition, a grid voltage synchronization method based on decoupled multiple synchronous reference frame PLL (DMSRF-PLL) is proposed. This DMSRF-PLL employs the positive, negative sequence and low-order harmonics dq transformation and their decoupling to achieve high speed and high performance output under asymmetric and harmonic condition for frequency, phase and positive, negative sequence dq components picking up. The measured results verified the performance of the proposed DMSRF-PLL method under complex grid condition. When applied to direct-driven wind power system connected to grid, the simulation result also shows that this method can eliminate the influence of the grid voltage harmonic on the output current.The power relationship is analyzed first based on the gird fault characteristics, and the challenges faced by wind turbine (take PMSG as a reference) under fault operation are summarized to two categories, active power imbalance and power fluctuation problems.The first problem is introduced by the dipping of positive-sequence grid voltage, while the second one is contributed by negative-sequence grid voltage. The reported fault ride-through control schemes are reviewed according to the summarized two challenges. The pros and cons of each control methods are identified. Finally, the further researches in direct-drive wind turbine fault ride-through control are discussed.A novel control method of PMSG wind turbine is proposed in this paper according to the problems caused by wind turbine which operated under asymmetric fault. This method can eliminate the grid side negative sequence current component and 2nd order voltage ripple in the dc link at the same time. The proposed control method employs the grid voltage feed forward to reduce the grid side negative sequence current component, while a novel power control concept, output power of generator tracking the grid side power, is applied to control the electro-magnetic power of the PMSG to eliminate the 2nd order voltage ripple in the dc link. Simulation results show that the proposed control method is effective under varies of fault conditions.To verify the accuracy of the proposed DMSRF-PLL, the three-phase grid-connected converter experimental prototype with digital control is developed, and detailed design process of software and hardware is given. Experimental verification of DMSRF-PLL method is test, this prototype is tested, The measured results verified the performance of the proposed DMSRF-PLL method under complex grid condition. The prototype is tested at the situation of steady working and the experimental results更多还原