【作者】 吴国祥；

【导师】 陈国呈；

【作者基本信息】 上海大学 ， 电力电子与电力传动， 2009， 博士

【摘要】 在能源枯竭与环境污染问题日益严重的今天,风力发电已经成为绿色可再生能源的一个重要途径。双馈电机变速恒频(VSCF)发电是通过对转子绕组的控制来实现的,而转子回路流动的功率是由发电机运行范围所决定的转差功率,因而可以将发电机的同步转速设定在整个运行范围的中间。如果系统运行的转差率范围为±30%,则最大转差功率仅为发电机额定功率的30%,因此交流励磁变换器的容量可大大减小,从而降低成本。该变换器如果加上良好的控制策略,则系统运行将具有优越的稳态和暂态运行性能,非常适用于风能这种随机性强的能源形式。本文对变速恒频双馈机风力发电系统的若干关键技术,如空载柔性并网、带载柔性并网、解列控制、最大功率点跟踪、电网电压不平衡运行、低电压故障穿越等问题进行了深入研究。论文的主要工作如下:根据交流励磁变速恒频风力发电的运行特点,将电网电压定向的矢量控制方法应用在双馈发电机的并网发电控制上。研究了一种基于电网电压定向的双馈机变速恒频风力发电柔性并网控制策略,在变速条件下实现无电流冲击并网和输出有功、无功功率的解耦控制,建立了交流励磁发电机柔性并网及稳态运行的控制模型,对柔性并网及其逆过程的解列分别进行了仿真和实验研究。提出了一种以向电网输送净电能最多为目标的最大功率点跟踪控制策略,在不检测风速情况下,能够自动寻找并跟随最大功率点,且不依赖风力机最佳功率特性曲线,提高了发电系统的净输出能力,具有良好的动、静态性能。仿真和实验结果证明了本控制策略的正确性和有效性。对网侧变换器分别进行了幅相控制和直接电流控制策略的研究。结果表明:幅相控制策略简单实用,可以得到正弦波电流,且波形谐波小,实现了单位功率因数运行,但响应速度相对较慢;而直接电流控制策略具有网侧电流闭环控制,使网侧电流动、静态性能得到提高,实现对系统参数的不敏感,增强了电流控制系统的鲁棒性,但算法相对复杂。在电网不平衡条件下,如果以传统的电网电压平衡控制策略设计PWM整流器,会使系统出现不正常的运行状态。为了提高三相PWM整流器的运行性能,本文对电网电压不平衡情况下三相PWM整流器运行控制策略进行了改进,研究了消除负序电流和抑制输入功率二次谐波的控制策略,实现了线电流正弦、负序输入电流为零及总无功功率输入为最小的目标。为了提高VSCF风力发电系统的运行能力,本文对电网故障时双馈风力发电系统低电压穿越控制(LVRT)进行了研究,在不改变系统硬件结构的情况下,通过改变励磁控制策略来实现LVRT;在电网故障时使电机和变换器安全穿越故障,保持不脱网运行,提高系统的稳定性和安全性。更多还原

【Abstract】 Nowadays the problems of energy lack and environment pollution are more and more serious, wind power generation becomes an important approach as green regenerative energy. Variable speed constant frequency (VSCF) wind power generation of doubly fed induction generator (DFIG) is realized by controlling the rotor circuits. Power flows through rotor circuits is decided by slip, so synchronous speed can be set in the middle of running range of speed. If slip range is±30% , the maximum slip power is 30% of generator rated power. Thus, the capability of AC excited converters is reduced greatly, cost is decreased considerably.If good control strategy is added to the converter, superior steady-state and transient-state operation characteristics will be obtained. So it is especially suitable for the renewable energy generation such as wind power generation. In this paper some key technologies,such as flexible cutting in and off, maximum power point tracking(MPPT) control strategy for variable-speed constant-frequency wind power generation and PWM rectifier operating in unbalanced voltage condition, fault ride-through are studied deeply. The contributions of this dissertation are as follows:According to characteristic of AC-excited variable speed constant frequency wind power generation, vector control technique is applied in doubly fed induction generator. Flexible cutting-in control strategy is studied based on grid voltage orientation without overshoot current, decoupling control of active power and reactive power is obtained. The modes of flexible cutting in and running in ready state are established. Flexible cutting in and its inverse process cutting off are studied by simulations and experiments.A novel maximum power point tracking control strategy is presented in this paper to deliver the most power to grid. The maximum power point can be tracked automatically not measuring wind speed in this control strategy and the control is independent of optimal turbine power curve, which has excellent dynamic, static performance. Simulation and experimental results confirm the accuracy and validity of this control strategy.Direct current control and phase-amplitude control strategies are investigated on grid-connected power converter. The algorithm of phase-amplitude control strategy is simple and practical, by which sinusoidal current can be get, harmonic components are small, unity power factor operation is achieved. But speed of response is relatively slow. Direct current control with current closed-loop control makes the dynamic and static performances of grid side current improved, is not sensitive to system parameters, and the robustness of control system is enhanced. But the algorithm is relatively complex.Under the unbalanced voltage condition, PWM rectifier designed according to balanced condition can not operate in normal state. To enhance the operating performance of the three-phase PWM rectifier, the control strategies in unbalanced input case are improved in this paper, which aims to suppress negative-sequence current and the secondary harmonic of input instantaneous power, to assure that line current is sinusoidal, component of negative sequence is zero, total reactive power is minimum.In order to improve the running performance of VSCF wind power generation, low voltage ride-through is investigated in this paper. A excitation control strategy is proposed for the rotor side converter in a doubly fed induction generator(DFIG) to allow the system to ride through a grid fault without changing system hardware. The machine and converter remain in the safe operating state, the stability and the security of system is thus enhanced.更多还原