【作者】 李辉；

【导师】 阳春华；

【作者基本信息】 中南大学 ， 控制科学与工程， 2011， 博士

【摘要】 目前,双馈型风力发电机普遍使用电压源型双PWM变频器作为励磁系统电源。双PWM变频器需要大电容作为直流储能元件,不仅体积大、重量重,且不易维护,同时大电解电容的电解液易于挥发,严重影响变频器的寿命。矩阵变换器不存在大电容或大电感,具有体积小,易维护等优点,因此研究矩阵变换器交流励磁系统,对减小励磁系统体积,提高功率密度,降低维护成本均有重要意义。但由于矩阵变换器本身结构复杂,控制难度大,将其应用于双馈电机交流励磁系统,还存在着并网困难、运行性能欠佳等问题。为此论文研究了基于矩阵变换器励磁的双馈型风力发电机并网运行控制策略,并通过实验和仿真验证了所提控制策略的有效性。论文的主要研究内容及创新性工作如下：(1)在深入分析双馈电机数学模型和矩阵变换器调制策略的基础上,根据矩阵变换器励磁的双馈电机空载、正常工况下和非正常工况下三种运行状态,提出了基于矩阵变换器励磁的双馈型风力发电机并网运行控制方案。该方案使得基于矩阵变换器励磁的双馈型风力发电机可以满足在不同工况下并网运行的要求。(2)针对在矩阵变换器励磁的双馈电机并网瞬时定子冲击电流较大的问题,提出了定子电压闭环控制策略。该策略是将电网电压的幅值和相位作为给定值,定子电压幅值作为反馈值,实现对矩阵变换器虚拟逆变侧的电压幅值和相位控制,使定子电压准确跟随电网电压,并简化了复杂的解耦控制。实验结果表明,减少了并网瞬时双馈电机定子冲击电流。(3)针对传统的矩阵变换器励磁控制策略响应时间较长、超调量较大的问题,提出了基于矩阵变换器励磁的直接功率控制策略。该策略首先由定子有功功率误差、无功功率误差、定子电压和转子所处位置直接计算得到转子电压信号,再通过矩阵变换器间接空间矢量调制策略控制转子电压。该策略实现了在一个控制周期内消除定子侧有功功率误差和无功功率误差,并省去了转子电流闭环控制环节。因此该策略能够有效提高响应速度,减少超调量。(4)针对传统矩阵变换器励磁控制策略在电网电压扰动和电压不平衡等非正常工况下运行效果不理想的问题,分别提出了非线性最优控制策略和电压不平衡交流励磁控制策略。仿真结果表明,非线性最优控制策略在电网电压扰动情况下减少了定子电压、有功功率和定子磁链的调节时间；电压不平衡交流励磁控制策略在电网电压不平衡情况下,根据不同控制目标,可以分别消除定子负序电流、减少有功功率脉动或无功功率脉动。(5)研发了矩阵变换器交流励磁实验系统。该系统以DSP控制器为核心构成主控系统和以IGBT模块为开关器件构成主电路,并使用变频器驱动异步电动机模拟风机,实现了在正常工况下双馈型风力发电机向电网输出有功功率和无功功率的并网运行。更多还原

【Abstract】 Nowadays, Back-to-back PWM converter is widely used as power supply of excitation system in DFIG. But this converter needs a big capacitor for its DC energy storage, so it is very big and heavy, and it is difficult to maintain. Meanwhile, the electrolyte is easy to volatilize, which shortens the service life. Matrix converter has no large capacitor or large inductor. And it is small and easy for maintaining. Therefore, it is very significant to research matrix-converter-excitation in order to increase power density and decrease maintenance costs. The DFIG based on matrix-converter-excitation is difficult to cut in and lack of performance operating, because matrix converter has complicated structure and is difficult to control. Thus, the grid-connected control strategy of DFIG based on matrix-converter-excitation is studied. The effectiveness has been proved by experiments and simulation. The major achievements include:(1) After investigating the DFIG model and matrix converter modulation strategy, the grid-connected control strategy of DFIG based on matrix-converter-excitation is proposed for no-load condition, normal operating condition and abnormal operating condition. Thus, the strategy satisfies the grid-connected requirements under different running conditions.(2) Considering the large impact of the stator current of the DFIG based on matrix-converter-excitation at the instantaneousness of cutting-in, a closed-loop control strategy for stator voltage is proposed. This control system regards the grid voltage amplitude and phase as given value, and the stator voltage as feedback to control the virtual inverter-side voltage amplitude and phase of the matrix converter, so that the DIFG stator voltage precisely follows the grid voltage and the solution of complex decoupling control is simplified. The experimental results show that the impact current of the cutting-in is little.(3) Considering the problem of long response time and large overshoot of traditional control strategies for matrix-converter-excitation, a direct power control method for matrix-converter-excitation is proposed. Firstly, rotor voltage signal is directly calculated using the stator active power error, the reactive power error, stator voltage, and the location of rotor in the strategy. Secondly, the rotor voltage is modulated using the matrix converter space vector modulation strategy. Then the active power error and the reactive power error are eliminated in a fixed period. Meanwhile, the rotor current loop is not needed. The strategy is able to improve the response speed and diminish the overshoot.(4) Regarding to the incapability of the traditional control when the grid voltage is disturbed or imbalanced, nonlinear optimal control and voltage unbalance control are proposed separately. The Simulation results show that the duration of time to modulate the stator voltage and active power under the case of the grid voltage disturbance is reduced after adopting the nonlinear optimal control strategy, and the pulses of the active power and reactive power are decreased or the stator negative sequence current is eliminated by applying the voltage unbalance control strategy when the grid voltage is imbalanced.(5) The experimental equipment of matrix-converter-excitation system is developed. The system consists of a DSP controller as master control system, a main circuit in which the IGBT module is the switching device, and an inverter-driven induction motor to simulate fans. It achieves that the DFIG transmits active power and reactive power to the grid under normal operating conditions.更多还原