【作者】 赵阳；

【导师】 陈坚； 张凯；

【作者基本信息】 华中科技大学 ， 电力电子与电力传动， 2008， 博士

【摘要】 随着常规能源日趋匮乏,环境问题也日趋严重,风力发电在全世界正以前所未有的速度发展。由于变速恒频双馈风力发电技术能够实现风电机组和电网之间的柔性连接,提高了风电转换效率,并且作为主要控制部件的电力电子变换器容量仅为发电机转差率容量,高效经济的特点使其成为风力发电技术的重要发展方向,具有广阔的应用前景。本文对变速恒频双馈风力发电系统中双馈感应发电机的励磁矢量控制技术进行了较为深入的研究,主要内容如下:本文首先建立了双馈感应发电机稳态数学模型和等值电路,详细推导了双馈感应发电机转子励磁电压和电流与有功、无功功率以及转差率s之间的关系;定性分析了双馈感应发电机稳态运行特性;分析、论证了绕组折算和频率折算关系,对励磁电源变频器设计有指导意义。建立了双馈感应发电机并网运行、独立运行和空载运行的数学模型,以及三种运行状态下基于定子磁链定向的励磁矢量控制策略,并在Matlab\Simulink仿真平台上建立了相应的仿真模型,对变速恒频双馈风力发电系统三种状态的运行特性进行了仿真研究,验证了控制策略的正确性。根据整个风电系统运行要求,将并网运行双馈感应发电机的控制系统有功指令值分为定子侧有功功率、电磁转矩和转速,由此将其励磁控制策略分为电流模式控制和速度模式控制。提出并网型双馈感应发电机的速度模式控制优于电流模式控制,指出速度模式控制才能控制表征风电系统获得风能的状态变量——风力机转速。同时设计了电流内环、速度外环和功率外环控制器,建立了相应的仿真模型,验证了这一结论。详细分析了整个风力发电机组在电网电压不对称条件下运行产生不良后果的机理,指出双馈感应发电机建立在正序旋转坐标下的励磁矢量控制策略对转子负序电流无法进行有效控制是产生不良影响的本质原因。通过同时对正序和负序定子磁链进行定向,推导出正序和负序坐标系下并网型双馈感应发电机的数学模型,并得到适应于电网电压不对称条件下的励磁矢量控制策略。该控制策略包含了能对转子负序电流进行有效控制的负序控制系统。根据电网电压不对称带来的不良影响将负序控制系统的控制目标分为四类,推导出各控制目标下的转子负序电流指令值。对四种控制目标分别进行仿真,通过对仿真结果的分析得到了具有指导性意义的结论:负序控制系统是一个两输入多输出的系统,不可能解决电网电压不对称带来的所有问题;以抑制定子电流或转子电流不对称为控制目标效果相差不大,对抑制其它物理量脉动效果较好;以抑制电磁转矩为控制目标,需要以定、转子电流不对称为代价,但转速、定子无功功率以及整个风电系统向电网输出的有功功率等物理量的脉动同时得到抑制。构建了一套变速恒频双馈风力发电系统实验平台,研制了其中的核心部分——双PWM电压型变换器,包括转子侧变换器和电网侧变换器。在该实验平台上进行了系列实验研究:电网侧变换器空载启动、突加负载,带电池的能量双向流动,以及有功和无功功率的解耦控制,实验结果表明电网侧变换器能够为转子转差能量提供双向流动的通道,实现有功和无功功率的解耦控制,并且动、静态特性良好;双馈感应发电机采用转子侧并网方式进行并网,实验结果表明双馈风力发电系统投入平滑,没有电流冲击;并网型双馈感应发电机在超同步和亚同步运行下的运行特性实验,实验结果验证了双馈感应发电机励磁矢量控制策略的正确性。更多还原

【Abstract】 With the situation of energy source exhaustion and environmental pollution, the wind energy generation is gaining more and more attention around the world. The variable speed constant frequency (VSCF) wind energy generation system with doubly fed induction generator (DFIG) not only realizes flexible connection of mechanical-electric system, enhances wind-electric energy conversion efficiency, but also possesses the characteristics of small cubage, light weight because the transducer as AC excitation of DFIG only deals with slip power in double direction. So the research and application of the DFIG progress at a rapid rate in wind power generating application. VSCF wind energy generation system with DFIG and its control technology is studied in this paper. The primary contents and original contributions of this dissertation are as follows:The steady state mathematical model and its equivalent-circuit model of DFIG are established, and the interrelations of key physical parameters such as power, rotor current and slip are discussed. For this basis,issues about operational characteristics、power floating and static operation performance are qualitative analyzed. It also discusses the influence of winding translation and frequency translation on rotor voltage, rotor current, active power and reactive power, and indicates essence of that the transducer capacity is slip ratio of generator capacity.Mathematical models in the synchronous rotary coordinate of the grid-connection, stand-alone and no load DFIG are established respectively. The excitation vector control strategies based on stator-flux orientation of grid-connection, stand-alone and no load DFIG are also put forward. The simulation models of DFIG on three states on MATLAB/Simulink environments are established. The simulation results verify the DFIG vector control strategy, which realizes good static and dynamic performance and obtains decoupling control of active power and reactive power.The reference value of DFIG vector control system is generally the active power, the electromagnetic torque, or the rotor speed. The former two may be termed ’current-mode control’, and the last may be termed ’speed-mode control’. It presents that the system dynamic characteristics under speed-mode control are superior to the dynamic characteristics under current-mode control and brings forward the state space explanation that the speed-mode control can control the wind turbine speed which indicates the wind energy that the system achieves. It designs the gains of two typical PI controllers in the current inner loop and the speed outer loop under speed-mode control. Simulation results in MATLAB/Simulink are brought forward to verify the good static and dynamic performance of the designed closed-loop control system.The effect of unbalanced grid voltage on wind energy generation system is studied, and the essential reason is analyzed that DFIG traditional excitation vector control system which built in the synchronous rotary coordinate can not effectively control the negative sequence component of rotor current.By orienting the positive and negative components of stator flux at the same time, it deduces mathematical model of grid connection DFIG under the positive and negative rotary coordinates for the first time, and puts forward DFIG excitation vector control strategy suitable for the condition of unbalanced grid voltage. It classifies the control targets of negative control system into four kinds, and draws significative conclusions by analyze the simulation results that it can minimize oscillations in either active power, or electromagnetic torque, or stator or rotor currents with the proposed control strategy.At last, it designs and sets up an experimental set of small capacity. Based on the stator flux-oriented vector control, this paper puts forward the excitation vector control strategies for the grid-connected, stand-alone and no-load states of DFIG respectively. It also presents the difference between the no-load cutting-in control and direct cutting-in control. The experiment investigation was made to further verify the effect of the direct cutting-in strategy and excitation vector control strategy of grid-connected DFIG. The results offer a good review of cutting-in process and the dynamic and static performance of the grid-connected DFIG system.It designs and implements a laboratory platform of VSCF wind energy generation system with DFIG which main part is a set of dual PWM voltage-source converters that includes the rotor-side converter and grid-side converter. A number of experiment items are performed on this platform, which including the grid-side converter control, the DFIG output active and reactive power decoupled control at the super synchronous, synchronous and sub synchronous speed, cut in control at DFIG rotor side. The experimental results testify the validity of the theory and the control strategy proposed in this dissertation.更多还原