Mixed control strategy of a doubly fed induction machine

In this paper the doubly fed induction machine (DFIM) is supplied by two pulse width modulation (PWM) voltage inverters. The mixed control strategy proposed is divided into two parts: a variable structure control (VSC) as far as the electrical modes are concerned, and a general PI controller for the mechanical modes. It is linked with active power distribution between stator and rotor circuits. An original DFIM mathematical model is defined in a stator flux reference frame. Experimental results of transient and steady-state behaviour are presented. In this paper we focus our study to three operating ranges: the magnetizing range, step and steady-state speed response, load torque impact.     

Reactive power capability of doubly fed asynchronous generators

While synchronous generator reactive power capability has been extensively treated in the bibliography, reactive capability of doubly fed asynchronous generator (DFAG) has not yet been studied. This kind of generator is widely used in wind energy, and its reactive power capability must be known in order to plan the reactive capability of wind farms as required by grid codes. Active and reactive power output of DFAGs can be expressed as a function of the terminal voltage and the internal voltage, allowing the graphical representation of the power capability limits in a similar way as the synchronous generator.     

Dynamic response of doubly fed induction generator variable speed wind turbine under fault

The performance of doubly fed induction generator (DFIG) variable speed wind turbine under network fault is studied using simulator developed in MATLAB/SIMULINK. Simulation results show the transient behavior of the doubly fed induction generator when a sudden short circuit at the generator bus is introduced. After the clearance of the short-circuit fault the control schemes manage to restore the wind turbine's normal operation. The controller performance is demonstrated by simulation results both during the fault and after the clearance of the fault. A crowbar is used to protect the rotor converter against short-circuit current during faults.     

双馈感应发电机的直接功率控制策略

建立了单机与无穷大系统相连的双馈感应发电机(DFIG)数学模型,并以定子电压综合矢量恒定为控制约束,提出了一种双馈感应发电机的励磁控制策略。该控制策略仅需测量定子侧电压、电流信号,简化了控制系统。利用该策略对并网双馈感应发电机有功、无功稳态调节特性及机端三相对地突然短路的过渡过程进行了仿真研究。结果表明,该方法能够实现有功和无功的独立控制,且具有良好的动态性能。     

提高双馈风电机组LVRT能力的改进直接功率控制

双馈风力发电系统采用传统直接功率控制时,在发生低电压穿越(LVRT)后转子电流振荡较大,易引起Crowbar再动作。建立传统直接功率控制下双馈风力发电系统的模型,对矢量控制和直接功率控制抑制LVRT的效果进行分析,在此基础上提出一种改进型直接功率控制方法。引入谐振调节器消除定子磁链动态分量对转子磁链的作用,抑制Crowbar切除后转子电流的动态分量,从而改善双馈风电机组LVRT特性。仿真比较验证了所提控制方法应用于双馈风力发电系统的可行性,该控制方法比矢量控制使系统更快恢复稳定,且比传统直接功率控制对转子电流振荡抑制效果更明显。     

Grid-fault ride-through analysis and control of wind turbines with doubly fed induction generators

This paper deals with the low voltage ride-through (LVRT) control of wind turbines with doubly fed induction generators (DFIGs) under symmetrical voltage dips. The investigation first develops a mathematical formula for the rotor current and rotor voltage when DFIG is subjected to a symmetrical voltage dip. From the analysis, the reasons of rotor inrush current and factors influencing it are inferred. Then, a control scheme enhancing the wind turbine LVRT capability is designed and simulated. The proposed control scheme consists of a nonlinear control strategy applied to the rotor-side converter and a dc-link voltage control applied to the grid-side converter. It improves the damping of DFIG transient response and minimizes oscillations of rotor current, electromagnetic torque and dc-link voltage during the generator voltage dip. It also limits the peak value of these quantities. At the end, results of theoretical analyses are verified by time domain simulations.     

基于双馈风电机组的分布式动态无功支撑系统

充分挖掘风电机组的无功电压调节能力对改善电力系统的电压稳定性有重要意义。首先定量分析了实际商用双馈风电机组的无功调节能力及限制因素,指出双馈风电机组具备较强的无功功率输出和吸收能力。继而提出了一种利用双馈风电机组的电力系统分布式动态无功支撑系统的构想及其实现方案。该系统可充分发挥双馈风电机组的动态无功调节能力,有效提高电力系统的动态无功储备,并显著改善双馈风电机组接入电网的电压稳定性。实际浙江电网的仿真结果验证了该技术的可行性和有效性。     

On the stability of power systems containing doubly fed induction generator-based generation

This article is concerned with the impact of large-scale wind farms utilising doubly fed induction generators on the stability of a general power system. Inspection of the eigenstructure of the power system provides a foundation for assessing the impact, which is then quantified by means of detailed numerical simulations.     

Effect of wind parks with doubly fed asynchronous generators on small-signal stability

This paper investigates modes of response introduced by wind parks with doubly fed asynchronous generators (DFAGs), as well as their impact on electromechanical oscillations in interconnected power systems. A DFAG model with detailed control loops is used, as it appears in the literature and commercial software. It is shown that under certain conditions and without appropriate controller tuning the voltage/VAR control loop of an interconnected DFAG tends to instability. Furthermore, the effect of increased penetration of DFAGs on the stability of inter-area oscillations in a small typical power system is examined. It is shown that the effect is generally favorable, but there are cases where the inter-area mode is less damped or can even be destabilized. Improved controller tuning to avoid instability in the latter case is proposed.     

双馈风机三相短路电流特性分析

双馈风机(DFIG)短路电流特性与传统电机相比存在显著差异。根据机端电压的跌落程度,分析了计及Crowbar保护动作和计及RSC控制两种情况下DFIG的短路电流特性。针对撬棒(Crowbar)保护动作后转子磁链的频率含量以及定、转子电流的解析表达式并未完全统一的问题,建立了DFIG数学模型,分析Crowbar保护动作后DFIG定、转子磁链的暂态过程。在此基础上采用拉氏和反拉氏变换法推导了转子磁链的表达式,通过数学解析的方法得到了计及Crowbar保护动作的DFIG定、转子电流计算表达式。同时根据DFIG数学模型和转子侧变流器(RSC)控制模型,采用解微分方程法详细地推导了计及RSC控制的双馈风机定、转子短路电流的表达式。最后在Matlab/Simulink平台上建立DFIG电磁暂态仿真模型。仿真验证计及Crowbar保护和计及RSC控制两种情况下DFIG短路电流表达式的正确性,进而分析了电压跌落程度、Crowbar阻值以及PI控制参数对短路电流的影响。     

Multiple models decentralized coordinated control of doubly fed induction generator

In this paper, a multiple model optimal tracking control (MOTC) design method for the double fed induction generator (DFIG) using correlative measured technique is proposed. The DFIG is represented by a third-order model, where electro-magnetic transients of stator are neglected. By using the correlative measured technique, the correlative measured matrix (CMM) of wind power system is obtained firstly. Then, a nonstandard state space equation of DFIG is obtained with the correlative measured vectors (CMVs), which reflect interactions between the DFIGs and grid. In order to cope with nonlinearities and continuous variation in the operating points, a multiple model design method is proposed in the discrete domain. The obtained control law, synthesized by using Bayesian probability, only depends on the local measured parameters. Hence, the MOTC can be regarded as a decentralized coordinated control, which can simplify the control structure and improve the transient stability of DFIG. To illustrate the effectiveness of the proposed MOTC strategy, simulations on a hybrid wind thermal power (HWTP) system are performed. The results show that the proposed MOTC strategy can provide acceptable performance throughout the whole operating region. Comparing to the conventional PID control, transient stability, damping, and fault ride-through capability of DFIG with the proposed MOTC design method have been improved effectively.     

双馈风力发电机三相短路电流分析

为了研究双馈风力发电机组的低电压穿越控制问题,分析了双馈风力发电机定子端三相短路时短路电流的产生机理,给出了双馈风力发电机在空载同步转速条件下的定转子短路电流的近似解析表达式.在此基础上,根据双馈风力发电机内部的电磁关系,分析了发电机故障前不同转速、输出有功功率及无功功率等运行状态对双馈发电机短路电流的影响.在理论分析的基础上,建立了3 MW双馈风力发电机的模型,对发电机定子端三相短路故障状态进行了仿真研究.仿真结果表明:通过定转子短路电流的近似解析表达式和发电机故障前的初始状态可以有效对双馈发电机短路电流进行定性分析,为进一步研究双馈风力发电机的低电压穿越能力提供了理论依据.     

Mathematical modeling and analysis of brushless doubly fed reluctance generator under unbalanced grid voltage condition

The brushless doubly fed reluctance generator (BDFRG) can be an attractive choice for wind power application where mostly located at remote areas with unbalanced grid voltages, however there is not any study on the BDFRG under this condition up to now. In this paper, a mathematical model for the BDFRG under unbalanced grid voltage condition has been developed. Its equivalent circuit in dq reference frames has been extracted, and the torque and power equations have been derived, all based on the positive and negative sequence components. Also, a real-time separation method has been proposed to separate the BDFRG positive and negative sequences. The developed model and equations express the basis of the BDFRG operation under unbalanced grid voltage condition. The proposed model is simulated in MATLAB/Simulink software and the accuracy of the proposed model and equations has been validated by comparison with simulation results of an existing BDFRG model under balanced condition, which has already been experimentally verified in the literature.     

Impact of FACTS controllers on the stability of power systems connected with doubly fed induction generators

The increasing power demand has led to the growth of new technologies that play an integral role in shaping the future energy market. Keeping in view of the environmental constraints, grid connected wind turbines are promising in increasing system reliability. This paper presents the impact of FACTS controllers on the stability of power systems connected with wind energy conversion systems. The wind generator model considered is a variable speed doubly fed induction generator model. The stability assessment is made first for a three phase short circuit without FACTS controllers in the power network and then with the FACTS controllers. The dynamic simulation results yield information on (i) the impact of faults on the performance of induction generators/wind turbines, (ii) transient rating of the FACTS controllers for enhancement of rotor speed stability of induction generators and angle stability of synchronous generators. EUROSTAG is used for executing the dynamic simulations.     

含双馈风机的配电网模糊谐波潮流计算

针对配电网中存在着大量的不确定因素对接有双馈风机的配电网节点进行基波和谐波模糊建模.并考虑节点内部存在的关系:在节点基波建模中,考虑并联补偿器和功率因数的关系可以提高理论收敛程度;在节点谐波建模中,考虑风机负荷、无源负荷和非线性负荷的关系可以极大简化模糊谐波建模的复杂程度.最后把双馈风机接入典型33节点辐射型配电网进行...     

并网双馈异步风电机组模糊自适应控制

介绍了双馈感应风力发电系统运行的基本原理。在变风速下,根据最大功率跟踪控制原理,利用发电机输出功率误差和发电机的转速误差,提出用模糊控制器代替风速测速仪来跟踪发电机的最佳转速,保证在额定风速下,使风机运行在最佳叶尖速比,风能利用率最佳,避免了湍流塔影等因素对风速测量的影响。同时,在外环功率PI调节器中,引入模糊控制来提高在额定风速下双馈感应发电机功率解耦的快速跟踪。最后,通过对整个风电系统包括风力机、双馈感应电机(含网侧及转子侧变换器)、控制器(含网侧及转子侧控制器)进行建模及仿真来验证模糊控制策略的可行性。     

Experimental validation of doubly fed induction machine electrical faults diagnosis under time-varying conditions

This paper investigates a new diagnosis technique for incipient electrical faults in doubly fed induction machine for wind power systems under time-varying conditions. The proposed method is based on currents frequency sliding pre-processing, and discrete wavelet transform thereby. The mean power calculation of wavelet signals, at different resolution levels, is introduced as a dynamic fault indicator for quantifying the fault extents. The approach effectiveness is proved for both stator and rotor faults under speed and fault varying conditions. Simulation and experimental results show the validity of the developed method, leading to an effective diagnosis procedure for stator and rotor faults in doubly fed induction machines.     

改善双馈感应发电机无功特性的变阻值撬棒保护方案

撬棒保护的接入及其电阻值会改变低电压穿越期间双馈感应发电机(DFIG)的无功功率动态特性,由此将影响风电场周边区域电网电压稳定性。针对这一问题,详细分析不同电网电压跌落水平和低电压过渡不同时期撬棒保护接入对DFIG无功特性的影响机理及其变化规律。提出了一种改善机组无功特性的变阻值撬棒保护方案,制定了该方案的撬棒阻值整定方法及其投切控制策略,并进行仿真对比研究。仿真结果表明,相比以限流为目标的传统撬棒保护和以尽快恢复机组可控性的主动式撬棒保护,所提撬棒保护方案不仅能在故障持续期间缩短撬棒投入时间,减少撬棒投入期间DFIG吸收的无功功率,提升出口电压。同时也能最大限度降低故障切除时的DFIG无功振荡峰值,加速电网电压恢复,有助于系统区域电压稳定性的提升。     

三相电压对称跌落双馈风电机组转子电压特性分析

针对电网故障产生的三相电压对称跌落,通过对电压跌落期间双馈风电机组（Doubly fed induction generator,DFIG）磁链和转子电压动态过程的详细论述,揭示了转子侧变换器在电压跌落期间不能提供足够的控制电压是造成转子侧过流的根本原因.以一台商用风电机组为例,得出电网电压不同程度跌落时,转子电压最大幅值-转差率特性,并计算出转子侧变换器所能输出的最大理论幅值.最后提出增强双馈风电系统在电压跌落期间运行能力的控制对策和保护措施.     

不对称故障下双馈感应发电机转子电压分析

针对不对称故障引起的电压跌落,求解得出三种不对称故障期间转子感应电动势峰值,结合对转子侧变流器控制能力的分析揭示了转子侧过流的根本原因。以转子侧变流器的最大控制电压为准则,推导出三种不对称故障的低电压穿越域。采用PSCAD搭建带有撬棒保护Crowbar的双馈风电机组暂态模型,仿真结果验证了所提出的低电压穿越域的正确性。