新型内馈式转子励磁高压风力发电机及其并网控制研究

发布时间：2018-08-25 13:20

【摘要】：伴随着电力电子技术的蓬勃兴起,发电机及其能量交换装置的功能更加成熟。风力发电机的功率转换水平已经从基本的千瓦级跨越到了兆瓦级,尤其是随着海上风电的蓬勃兴起,研究高压大容量的风力发电机已经成为当今乃至今后风力发电技术进步的新热点之一。现在,高压风力发电系统多由下面的组合方式构成:一种采用高压风力发电机、高压变流器组合;一种采用低压风力发电机、低压变流器、变压器组合。由于高压变流器存在造价高、系统结构繁复、控制系统要求高等缺点,大容量发电机普遍采用第二种组合方式。但是随着发电机容量的扩大,发电机定子端较低的输出电压会导致机端输出电流升高,这不仅需要载流量更大的电缆与铜排,并且使风力发电机的生产工艺变得更为复杂。另外,定子端电压较低,在并入电网前一般需要两个甚至多个变压器进行升压,而在网侧变流器在与电网相连之前也需要增加一个降压变压器为其提供电源支撑,这些无疑都增加了系统的制造成本与运行成本。为解决高压风力发电机存在的难题,本文主要研究工作和创新点如下:(1)在双馈风力感应电机(DFIG)的结构和工作原理的基础上,提出了一款新型内馈式转子励磁高压风力发电机(Internally Fed Rotor Excitation Generator—IFREG)。该风力发电机定子设有两套同槽布线的定子绕组,一套是高压定子主绕组,输出端可直接连接大电网,输出恒频恒幅的交流高电压;另一套是低压定子辅助绕组,连接定辅侧PWM变流器,通过直流母线、转子侧PWM变流器可以向发电机输入励磁电流,解决了内馈式转子励磁高压发电机在风速与负载情况都发生变化时,所需要的励磁电流调节问题。通过相应的励磁启动控制策略、柔性并网控制策略以及稳态运行控制策略,IFREG可以有效保持其定子端感应电压频率、幅值的恒定,取消或减少变压器的数量,有效地降低系统的成本。(2)根据课题要求设计了一台6kV、440kW样机,并采用有限元方法对其在空载、负载状况下进行了亚同步、同步和超同步有限元仿真实验,从原理上检验了 IFREG在变速恒频(VSCF)领域的可行性。(3)系统地推导了 IFREG发电系统在abc和dq坐标下的数学模型;提出了IFREG的励磁启动方式及其控制策略。根据其数学模型搭建了 IFREG的Matlab模型,并对离网状况下IFREG在不同转速下进行了仿真分析,仿真结果与有限元仿真结果基本相同,验证了所搭建数学模型的准确性。仿真结果还表明:在离网状态下,处于不同风速情况下的内馈式转子励磁高压风力电机可以定子端获得频率幅值稳定的高电压输出。(4)研究了内馈式转子励磁高压风力发电系统在电网电压稳定状态下定辅侧PWM变流器的数学模型,探讨了定辅侧PWM变流器的双闭环控制策略,并在此控制策略的基础上提出了一种基于励磁启动电源的定辅侧变流器功率补偿控制策略。推导了 IFREG发电系统在电网电压稳定状态下转子侧变流器的运行机理,在此基础上提出了不同于普通双馈风力发电机的基于定子磁链定向的矢量控制方法和最大风能追踪控制策略。(5)提出了与IFREG系统相匹配的并网控制程序与控制策略。建立了 IFREG在网侧电压恒定状况下的仿真模型,对IFREG发电系统励磁启动性能、柔性并网性能、负载稳态运、有功无功解耦控制和最大风能追踪能力进行了仿真分析。(6)为了验证IFREG在变速恒频发电中的运行特性,研制了 440kW、6kV内馈式转子励磁高压风力发电样机,并搭建了系统实验平台。完成了一套可为内馈式转子励磁高压风力发电系统中电力电子开关器件进行供电的多路高压隔离供电系统。在实验平台上开展了励磁启动性能、柔性并网性能、负载稳态运行、有功无功解耦控制实验,实验结果与仿真结果相符合,证明了 IFREG及其发电系统的可行性以及文中所提控制策略的正确性。
[Abstract]:With the flourishing development of power electronics technology, the functions of generators and their energy exchange devices have become more mature. The power conversion level of wind turbines has leaped from the basic kilowatt level to the megawatt level. Especially with the flourishing development of offshore wind power, the study of high-voltage and large-capacity wind turbines has become the wind of today and even in the future. Nowadays, the high-voltage wind power generation system is composed of the following combinations: one is composed of high-voltage wind generator and high-voltage converter; the other is composed of low-voltage wind generator, low-voltage converter and transformer. However, with the expansion of generator capacity, the lower output voltage at the stator end of the generator will lead to the higher output current. This not only requires more cables and copper bars, but also makes the production process of the wind turbine more complicated. In order to solve the problem of high-voltage wind turbines, it is necessary to add a step-down transformer to the grid-side converter before it is connected with the grid, which undoubtedly increases the manufacturing cost and operation cost of the system. The main research work and innovations are as follows: (1) Based on the structure and working principle of doubly-fed wind induction machine (DFIG), a new type of internal-fed rotor-excited high-voltage wind generator (IFREG) is proposed. The stator winding is the main winding of the high-voltage stator, and the output end can be directly connected to the large power grid to output constant frequency and constant amplitude AC high voltage; the other is the low-voltage stator auxiliary winding, connected to the stator-auxiliary side PWM converter, through the DC bus, the rotor-side PWM converter can input excitation current to the generator, which solves the problem of internal-fed rotor-excited high-voltage generator in wind speed and wind speed. Through the corresponding excitation start-up control strategy, flexible grid-connected control strategy and steady-state operation control strategy, IFREG can effectively maintain the frequency and amplitude of the stator-end induced voltage, cancel or reduce the number of transformers, and effectively reduce the cost of the system. ( 2) A 6 kV, 440 kW prototype is designed according to the requirement of the project, and its sub-synchronous, synchronous and super-synchronous finite element simulation experiments are carried out under no-load and load conditions by using finite element method. The feasibility of IFREG in the field of variable speed constant frequency (VSCF) is verified in principle. (3) The number of IFREG power generation system in ABC and DQ coordinates is deduced systematically. The mathematic model of IFREG is established, and the simulation analysis of IFREG under different rotational speeds is carried out. The simulation results are basically the same as the finite element simulation results, which verify the accuracy of the mathematic model. In the off-grid state, the high-voltage output with stable frequency amplitude can be obtained at the stator end of the internal-fed rotor-excited high-voltage wind turbine under different wind speeds. (4) The mathematical model of the PWM converter at the stator-auxiliary side of the internal-fed rotor-excited high-voltage wind power generation system under the grid voltage stability is studied, and the PWM converter at the stator-auxiliary side is discussed. Based on the double closed loop control strategy, a power compensation control strategy of stator-auxiliary converter based on excitation start-up power supply is proposed. The operation mechanism of rotor-side converter in IFREG power generation system under grid voltage stability is deduced. On this basis, different from ordinary doubly-fed wind turbine is proposed. Based on the stator flux oriented vector control method and the maximum wind energy tracking control strategy. (5) A grid-connected control program and control strategy matching the IFREG system are proposed. A simulation model of IFREG system under constant grid-side voltage is established. The excitation start-up performance, flexible grid-connected performance, load steady-state operation, active and reactive power of the IFREG power generation system are analyzed. (6) In order to verify the operation characteristics of IFREG in VSCF power generation, a 440kW, 6kV internal-fed rotor-excited high-voltage wind power generator prototype was developed, and a system experimental platform was built. A set of power electronics for internal-fed rotor-excited high-voltage wind power generation system was completed. Experiments on excitation start-up performance, flexible grid-connection performance, steady-state load operation and active and reactive power decoupling control are carried out on the experimental platform. The experimental results are in agreement with the simulation results, which prove the feasibility of IFREG and its power generation system and the correctness of the control strategy proposed in this paper.
【学位授予单位】：山东大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TM315

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