High Efficiency Double–Fed Induction Generator Applied to Wind Power Generator Technical Analyses

High efficiency Double-Fed Induction Generator applies new power electronic technology, and utilizes vector control to fix the magnetic direction of the stator to the vertical axis. Adjusting the input current of rotor via an inverter can separately control the cross axis and vertical axis current of real power and reactive power of a generator. Traditionally, rotating speed affects frequency and the output is unstable. This study concentrates on high efficiency Double-Fed Induction Generators and Traditional Generators from mathematic model to derive and control the characteristics simulation and comparison than get an output of high efficiency Double-Fed Industrial Generators. This study utilizes the simulation software MATLAB/Simulink to simulate the response characteristics of vector control of a Double-Fed Industrial Generator. The operating and control functions are better than those of a traditional generator.

Steady State Analysis of a Doubly Fed Induction Generator

In this paper, we present the steady state analysis of a double-fed induction generator (DFIG) adopted for wind power generation. The three-phase induction machine connected to the network, to work as a generator for wind farms, is excited on the rotor circuit by a slip-frequency current injected to the rotor, from an exciter mounted on the same shaft of the machine. The resulting rotating magnetic field rotates at synchronous speed;as such the generated power has a constant frequency independent of the shaft speed. Effects of the excitation voltage magnitude and phase angle on the active and reactive power are studied, when the machine runs at constant speed. It has been shown that by controlling the excitation voltage magnitude and phase angle would control the mode of operation of the machine;motor mode or generator mode. Furthermore, the effects of the shaft speed on the active and reactive power at constant excitation voltage magnitude and constant phase angle are also investigated.

An analytic electromagnetic calculation method for performance evolution of doubly fed induction generators for wind turbines

An analytic electromagnetic calculation method for doubly fed induction generator(DFIG) in wind turbine system was presented. Based on the operation principles, steady state equivalent circuit and basic equations of DFIG, the modeling for electromagnetic calculation of DFIG was proposed. The electromagnetic calculation of DFIG was divided into three steps: the magnetic flux calculation, parameters derivation and performance checks. For each step, the detailed numeric calculation formulas were all derived. Combining the calculation formulas, the whole electromagnetic calculation procedure was established, which consisted of three iterative calculation loops, including magnetic saturation coefficient, electromotive force and total output power. All of the electromagnetic and performance data of DIFG can be calculated conveniently by the established calculation procedure, which can be used to evaluate the new designed machine. A 1.5 MW DFIG designed by the proposed procedure was built, for which the whole type tests including no-load test, load test and temperature rising test were carried out. The test results have shown that the DFIG satisfies technical requirements and the test data fit well with the calculation results which prove the correctness of the presented calculation method.

Effects of Wind Turbines Equipped with Doubly-fed Induction Generators on Distance Protection

Nowadays wind energy is the fastest growing renewable energy resource in the world.The problems of integrating wind farms are caused by changes of wind speed during a day.Moreover,the behaviors of wind turbines equipped with doubly-fed induction generators differ fundamentally from synchronous generators.Therefore,more considerations are needed to analyze the performances of the distance protection relays.The protection of a wind farm with distance relay is inspected.By changing the conditions of the wind farm,the characteristics of the distance relay are studied.

Reactive Current Allocation and Control Strategies Improvement of Low Voltage Ride Though for Doubly Fed Induction Wind Turbine Generation System

为满足风电机组低电压穿越（low voltage ride through,LVRT）的测试要求及其电气模型一致性评估需要,提出考虑向电网注入无功电流的双馈风电机组LVRT的控制策略。在阐述风电机组LVRT测试要求及控制原理的基础上,推导双馈发电机（doubly fed induction generator,DFIG）定子侧及网侧变流器输出无功电流极限表达式,研究电网电压跌落深度和发电机总输出有功功率对其无功电流极限值的影响规律,进而提出DFIG在LVRT期间的无功电流分配算法和改进的有功、无功功率控制策略。最后,以某实际2 MW双馈风电机组为例,分别对风速为5和12 m/s、电网电压对称跌落至20%和50%工况下的LVRT运行性能进行仿真比较和样机测试。与传统LVRT控制方法的对比表明,所提改进控制策略能更好地满足风电机组LVRT的测试要求。样机测试结果进一步证明了改进控制策略和仿真模型的有效性。

适应并离网模式切换的DFIG电磁暂态仿真建模

目前,常用的商业仿真软件中的双馈式感应发电机(double-fed Induction Generator,DFIG)模型通常不支持离网运行模式,难以实现风力发电系统由离网到并网的全过程电磁暂态仿真,对电力系统仿真分析工作带来极大不便。研究适应并离网模式切换的DFIG电磁暂态仿真建模方法。基于模块化思想分别对风力机、异步电机、变流器以及断路器进行建模,在系统组装形成DFIG风力发电系统电磁暂态仿真模型。提出了适应并离网模式切换的DFIG受控源等效电路模型和离散时间域实现方法,通过设计状态变量矩阵元素的截取和扩充算法实现了模型在并离网模式下的无缝衔接。在MATLAB/Simulink中搭建DFIG发电系统模型对所提方法和模型进行验证,仿真结果表明,所提建模方法能够很好地支持DFIG离网运行模式,实现DFIG由离网到并网的全过程电磁暂态仿真。

计及风力发电机转速安全约束的DFIG一次调频模型预测控制策略

针对传统方法控制双馈感应发电机(DFIG)的调频效果过于依赖参数整定的问题,该文提出了一种基于模型预测控制(MPC),计及转速安全约束的风力发电机参与一次调频控制策略。该方法结合风力发电机动力学模型与频率响应模型建立预测模型,通过线性回归方法变参考值将风力发电机转速的稳定性纳入考虑。相较于虚拟惯性控制等方法将系统频率偏差与转子动能直接关联,该文方法通过建立全新的预测模型,实时统筹考虑整个系统的状态信息,无需反复调整参数,在考虑转速安全性的同时兼顾全局性能。最后,通过实际算例分析验证了该文调频策略的有效性以及相对现有方法的优越性。

一种多地DFIG联动控制的多馈入受端系统连续换相失败抑制策略

我国沿海负荷中心呈现直流多馈入的结构特征,海上风电的大规模开发使得系统在非正常工况下容易诱发次同步振荡,电压的快速波动可能会造成连续换相。针对该现象进行机理分析,通过优化双馈风电机组(doubly fed induction generator,DFIG)的控制方法,有效抑制了次同步振荡。同时,针对不同区域风电场调节能力差异,通过关联各直流落点的多馈入交互作用因子(multi-infeed interaction factor,MIIF),充分调动不同区域风电场的补偿能力抬升系统电压。该方法有效地抑制直流多馈入系统的异地连续换相失败。最后,通过PSCAD仿真对比验证所提策略的有效性。

不平衡电压下的DFIG模型预测直接功率控制

为提高双馈风力发电机在不平衡电网电压工况下的运行性能,提出一种扩张状态观测器与模型预测控制相结合的直接功率控制策略。首先,采用扩张状态观测器对系统中因负序分量引起的不确定项、模型误差及外部扰动等不确定因素进行参数估计。然后,结合模型预测控制理论建立双馈风力发电机模型预测直接功率控制数学模型。最后,针对不平衡电网电压下的功率振荡分量讨论功率优化补偿方案。仿真结果验证了所提方法的有效性。

基于LESO的DFIG-GSC反馈线性化直接功率控制

为了提高双馈风力发电机网侧变换器(DFIG-GSC)这个强耦合非线性系统的性能,提出了一种反馈线性化直接功率控制策略。首先在αβ坐标系下建立以有功功率、无功功率为变量的DFIG-GSC的数学模型,针对模型中的强耦合项采用反馈线性化进行解耦,得到其线性模型,再结合滑模控制理论设计出功率内环的控制律。由于功率内环控制律中未建模部分和不确定因素会对控制效果产生影响,采用线性扩张状态观测器对其进行观测并对其控制量进行修正。同时电压外环采用滑模控制来提高直流侧电压的响应速度。最后搭建仿真模型与传统PI控制以及直接功率控制进行比较,验证了所提控制策略的合理性和有效性。

基于扩张状态观测器的DFIG网侧变换器滑模控制

针对双馈风力发电机网侧变换器因负载变化和滤波参数摄动导致控制效果不佳的问题,文中提出一种扩张状态观测器(extended state observer,ESO)与滑模控制相结合的网侧变换器双闭环控制策略,内环采用以功率为状态变量的基于ESO的滑模直接功率控制,外环采用以电压平方为状态变量的基于ESO的滑模控制。首先,应用ESO对系统状态变量与包含系统未建模动态、负载变化和滤波参数摄动等不确定项进行估计,无需系统的精确数学模型即可设计滑模控制方法,实现网侧变换器在复杂环境下的鲁棒控制。此外,引入功率差前馈环节,可减小负载变化时外环滑模控制非线性带来的冲击。最后,对负载变化和滤波参数摄动2个算例进行仿真。结果表明,与传统矢量控制和滑模控制相比,所提控制策略在复杂环境下具有更强的鲁棒性。

基于DFIG稳态有功功率下限和电网小扰动稳定灵敏度的DFIG有功功率备用容量范围

随着风电并网的快速增加,要求风电机组如双馈感应风电机组(doubly-fed induction generator,DFIG)参与电网有功平衡和频率稳定,为此需要确定其有功功率备用容量范围。提出了超速模式下确定DFIG有功功率备用容量范围的方法。建立了并网DFIG的潮流模型,计及转速与转子侧变流器(rotor-side converter,RSC)的容量约束,确定了DFIG稳态有功功率下限。在此运行方式下,对电网进行了特征值分析以发现危险模式。考虑转差率影响初值和状态矩阵,拓展了潮流雅可比矩阵,建立了危险模式对转差率灵敏度的解析表达。根据上述灵敏度,筛选出与转差率强相关的危险模式,通过调节PI参数或/和转差率以消除危险模式。最后根据转差率取值确定出DFIG有功功率的备用容量范围。算例仿真结果验证了所提算法的正确性和控制效果。

Phase–amplitude model for doubly fed induction generators

The doubly fed induction generator(DFIG) is major type of wind turbine generator used in grid-connected wind farms. Practical models of DFIG have been built to study the influence of wind power generation on power system dynamics. However, most existing practical models of the DFIG are based on rectangular coordinates,in which frequency variation is neglected. In this paper, a phase-amplitude(P-A) model is proposed for a DFIG based on phase and amplitude of the internal voltage. The model structure is much like that of the synchronous generator, and the rotor voltage can manipulate both the amplitude and the phase of the internal voltage.Comparisons have been made between the new P-A model of the DFIG and the synchronous generator model,as well as the asynchronous motor model.The contributions of the new P-A model of the DFIG are discussed and it is demonstrated that the proposed model has better ability in describing power system dynamic phenomena such as voltage dynamics and structural dynamics. Simulation results and a field test validate these contributions.

Robust control based on the Lyapunov theory of a grid-connected doubly fed induction generator

This paper discusses the robust control of a grid-connected doubly-fed induction generator （DFIG） controlled by vector control using a nonlinear feedback linearization strategy in order to ameliorate the performances of the control and to govern the developed stator active and reactive power in a linear and decoupled manner, in which an optimal operation of the DFIG in subsynchronous operation is given, as well as the control stator power flow with the possibility of keeping stator power factor at a unity. The use of the state-all-flux induction machine model gives place to a simpler control model. So, to achieve this objective, the Lyapunov approach is used associated with a sliding mode control to guarantee the global asymptotical stability and the robustness of the parametric variations.

计及不同电压跌落和GSC馈出电流的DFIG精细化故障计算模型

当含双馈感应发电机(DFIG)的交流电网发生故障时,DFIG输出特性的精确性将影响到整个故障网络计算结果的准确性。首先,从DFIG的不同电压跌落出发,详细推导了撬棒保护投入、转子侧变流器(RSC)励磁控制和外环控制下DFIG定子侧输出电流的计算公式。接着,考虑网侧变流器(GSC)的馈出电流,推导了GSC和RSC在不同控制策略下DFIG的输出电流表达式,进而提出了计及不同电压跌落和GSC馈出电流的DFIG精细化故障计算模型。最后,在MATLAB/Simulink平台中进行了DFIG并入无穷大系统和典型电网仿真来验证该精细化模型的准确性。仿真结果表明,所提精细化模型理论计算值与仿真值误差较小;与现有模型相比,该模型在应用于电网故障计算时具有更高的准确性。

Doubly-fed induction generator drive based WECS using fuzzy logic controller

The purpose of this paper is to improve the control performance of the variable speed, constant frequency doubly-fed induction generator in the wind turbine generation system by using fuzzy logic controllers. The control of the rotor-side converter is realized by stator flux oriented control, whereas the control of the grid-side converter is performed by a control strategy based on grid voltage orientation to maintain the DC-link voltage stability. An intelligent fuzzy inference system is proposed as an alternative of the conventional proportional and integral （PI） controller to overcome any disturbance, such as fast wind speed variation, short grid voltage fault, parameter variations and so on. Five fuzzy logic controllers are used in the rotor side converter （RSC） for maximum power point tracking （MPPT） algorithm, active and reactive power control loops, and another two fuzzy logic controllers for direct and quadratic rotor currents components control loops. The performances have been tested on 1.5 MW doubly-fed induction generator （DFIG） in a Matlab/Simulink software environment.

Application of fuzzy logic control algorithm as stator power controller of a grid-connected doubly-fed induction generator

This paper discusses the power outputs control of a grid-connected doubly-fed induction generator （DFIG） for a wind power generation systems. The DFIG structure control has a six diode rectifier and a PWM IGBT converter in order to control the power outputs of the DFIG driven by wind turbine. So, to supply commercially the electrical power to the grid without any problems related to power quality, the active and reactive powers （Ps, Qs） at the stator side of the DFIG are strictly controlled at a required level, which, in this paper, is realized with an optimized fuzzy logic controller based on the grid flux oriented control, which gives an optimal operation of the DFIG in sub-synchronous region, and the control of the stator power flow with the possibility of keeping stator power factor at a unity.

Comparing the Quality of Power Generated from DFIG with Different Types of Rotor Converters

In this paper the quality of power generated from wind energy conversion system employing a double fed induction generator (DFIG) is investigated. The DFIG performance is tested with 3 types of converters interfacing the rotor with the grid. These are: the six-step thyristor inverter with diode rectifier, six-step IGBT inverter with diode rectifier, and 3-level IGBT-PWM inverter with diode rectifier. The harmonics in current and voltage, power factor value, and the transient behavior in each system are investigated and compared. Comparison is done at sub-and super-synchronous DFIG operational speed. In the system with lowest power quality passive filters or LC filter are added and improvement in system performance is recorded. From this study the optimum system from point of view of cost and control complexity is concluded.