Model and Performance of Current Sensor Observers for a Doubly Fed Induction Generator

Abstract—This article presents a stator and rotor current observer for a doubly fed induction generator. First, the dynamic models of the wind turbine drive train are presented, and the vector control strategies of a doubly fed induction generator for the rotor-side and grid-side converters are described. A stator and rotor current observer model, which is based on the state–space models of doubly fed induction generators, is then derived by using the stator and rotor voltage signals as inputs. To demonstrate the effectiveness of the proposed current observer, its dynamic performance is simulated using a MATLAB/Simulink software platform under the conditions of active power change of doubly fed induction generators and grid voltage dip fault. Furthermore, the robustness of the proposed current observer is investigated when the doubly fed induction generator rotor resistance is changed. Results show that the proposed observer has good coherence and robustness with the current sensor output when the doubly fed induction generator is in dynamic and transient responses. Compared with the referenced bilinear observer, the proposed observer has better fault-tolerant ability when the fault in the observed current sensor occurs.     

Performance of a grid-connected wind generation system with a robust susceptance controller

Wind turbine driven induction generators are vulnerable to transient disturbances like wind gusts and low voltages on the system. The fixed capacitor at the generator terminal or the limited support from the grid may not be able to provide the requisite reactive power under these abnormal conditions. This paper presents a susceptance control strategy for a variable speed wound-rotor induction generator which can cater for the reactive power requirement. The susceptance is adjusted through a robust feedback controller included in the terminal voltage driven automatic excitation control circuit. The fixed parameter robust controller design is carried out in frequency domain using multiplicative uncertainty modeling and H_∞ norms. The robustness of the controller has been evaluated through optimally tuned PID controllers. Simulation results show that the robust controller can effectively restore normal operation following emergencies like sudden load changes, wind gusts and low voltage conditions. The proposed robust controller has been shown to have adequate fault ride through capabilities in order to be able to meet connection requirements defined by transmission system operators.     

变速恒频双馈风电机组恒功率非线性控制

为了有效减少变速恒频双馈风电机组额定风速以上时的功率和转速波动,提出了一种同时考虑桨距角和双馈感应发电机转子励磁电压调节的新型恒功率控制策略。在分析风力机特性和双馈感应发电机基本电磁关系的基础上,建立了变速恒频双馈风电机组的非线性数学模型,并利用反馈线性化理论设计了非线性控制器。仿真结果表明,所提出的控制策略与现存的仅...     

交直流电力系统非线性鲁棒直流调制控制器设计

随着“西电东送、全国联网”战略的实施,大区之间通过交直流并列运行输电系统实现电网互联。性能优良的直流调制控制器可以快速有效地调节直流联络线的输送功率,减轻交流输电系统的暂态输电压力,以提高交流系统的动态性能。以交直流并列电力系统为研究对象,采用基于扩张状态观测器的动态反馈线性化方法,将系统的非线性数学模型动态补偿为一个伪线性系统,然后利用线性鲁棒H∞理论进行控制器综合。仿真试验表明,当交流联络线发生三相短路故障时,给出的控制器能够有效抑制两侧交流系统的功角振荡,且对于系统不确定性表现出良好的鲁棒性,从而使整个交直流电力系统的暂态稳定性得到改善。与基于精确反馈线性化方法的非线性控制器相比,具有更为优越的动态品质。     

Design of Novel Intelligent Controller for Doubly-Fed Induction Generator-Driven Wind Turbine to Improve Transient Control Performance

Abstract

This paper presents a design for the novel intelligent control (NIC) of the stabilization of a doubly fed induction generator (DFIG)-based wind turbine. The intelligent control scheme was developed to control the rotor side voltage source converter that allowed independent control of the generated active and reactive power as well as the rotor speed to track the maximum power point (MPP). Moreover, the NIC was used to reduce the interaction between the real and reactive power flow and improve the performance. The proposed NIC consisted of an improved recurrent fuzzy neural network (IRFNN) and ant colony optimization with genetic algorithms (GACO). GACO was adopted to adjust the learning rates to improve the online learning capability of the IRFNN. Furthermore, an NIC controller was proposed for both the rotor and stator side converters to improve the steady-state and transient voltage stability of the DFIG system for different operating conditions. In addition, the method is highly simple to implement. Finally, the proposed approach stabilized the internal dynamics through rotor voltage control and improved the dynamic behavior of the DFIG after clearing a fault.     

Smoothing of Wind Power Fluctuations for Permanent Magnet Synchronous Generator-Based Wind Energy Conversion System and Fault Ride-through Consideration

Due to the increment of penetration level of wind power generation, output power fluctuation is one of the most important issue's that can destabilize the power system operation. This article mainly deals with the smoothing of the output power fluctuations of a wind energy conversion system based permanent magnet synchronous generator and fault ride-through enhancement during a grid fault. The concerned wind energy conversion system based permanent magnet synchronous generator adopts an AC-DC-AC converter system. The proposed control method limits the wind energy conversion system output power by adjusting the pitch angle of the wind turbine blades when wind speed is above the rated wind speed. In the grid-side converter, a fuzzy logic controller is used to determine the torque reference for which the kinetic energy stored by the inertia of wind turbine can smooth the output power fluctuations of the permanent magnet synchronous generator. Also, the DC-link voltage, controlled by the grid-side inverter, is adjusted in accordance with the output power fluctuations of the permanent magnet synchronous generator using a voltage smoothing index. Moreover, in this aticle, the proposed method ensures that the wind turbine stays operational during grid faults and provides fast restoration once the fault is cleared. To show the effectiveness of the proposed method, simulations under different conditions have been performed by using MATLAB/Simulink® (The Math Works, Natick, MA, USA).     

带电压调节功能的非线性鲁棒控制器

提出了一种既可增加多机电力系统暂态稳定性又可达到机端输出电压调节功能的非线性鲁棒控制器。该控制器由一个直接反馈线性化（DFL）控制器和一个比例积分（PI）控制器组成。DFL控制器用于降低多机电力系统的非线性程度以及各机之间的相互作用。所提控制器设计方法既可保证系统稳定性又可达到调节电压的目的,同时在实现时不需要测量发电机功角。仿真结果表明,所提出的方案可在很宽的运行范围内增加系统的阻尼及稳定性。     

多机电力系统励磁控制的人工神经网络逆系统方法

基于各发电机的完整的实用三阶模型，通过将发电机内部的不可测变量转化为发电机端的可测变量，在未做任何近似或简化的情况下，实现了仅采用本地可测量的多机系统中各发电机励磁控制的精确线性化。在具体的励磁控制器设计中，选取机端电压作为被控量再附加电力系统稳定器(PSS)环节进行辅助控制，使得同时满足系统对电压稳定性和功角稳定性的控制要求；采用人工神经网络(ANN)逆系统方法实现精确线性化，避免了对系统精确数学模型的依赖，使文中方法更实用。针对一个2区域4机系统的仿真结果表明，安装ANN逆励磁控制器可以极大地提高被控机组的稳定性能，同时，全系统的稳定性也可以得到明显的提高。     

A method of damping transient rush voltage fluctuation of power systems due to a wind driven generator via nonlinear state feedback control

Squirrel-cage induction generators are widely used as generators for windmill power systems, because they are inexpensive, have high durability, and are capable of operating asynchronously with power systems. However, induction generators suffer the drawback that they cause transient rush currents that are several times larger than the rated value when connected to power systems. Also since wind energy is influenced by geographic and weather conditions, start/stop operations occur frequently for windmill power systems. Therefore, connecting induction generators to power systems causes undesirable voltage fluctuations in power systems, which is the major obstacle against the practical use of windmill generator systems. This motivates the study of transient rush current/voltage attenuation in windmill generator systems. In this paper, a nonlinear state-feedback controller for windmill power systems is proposed. The proposed controller globally asymptotically stabilizes the plant and effectively attenuates the transient current/voltage of these systems. Computer simulations using parameters for an actual windmill generator system also gave good results. © 1998 Scripta Technica, Electr Eng Jpn, 124(1):17–23, 1998     

STATCOM在风力发电场中的应用

在同步旋转坐标系下采用STATCOM(static synchronous compensator)和异步发电机风力发电系统的暂态数学模型,采用基于非线性反馈线性化的逆系统方法,构造出STATCOM的伪线性系统,然后采用滑模变结构控制理论设计出STATCOM的滑模变结构控制器。然后,以随机风和电网大扰动为例,采用STATCOM对并网风电场的电能质量和稳定性问题进行仿真。结果表明:采用该控制策略的STATCOM可很好地改善风电场的电能质量和稳定性。     

改善基于双馈感应发电机的并网风电场暂态电压稳定性研究

提出了改善基于双馈感应发电机的并网风电场暂态电压稳定性的措施以实现风电场的低电压穿越(low voltage ride through, LVRT)功能。目前，大部分基于双馈感应发电机的变速风电机组不具有故障情况下的暂态电压支持能力，当电网侧发生严重短路故障时，风电场的暂态电压稳定能力会影响到电网安全稳定。该文在DIgSILENT/PowerFactory中建立了具有暂态电压支持能力的变速风电机组转子侧变频器控制模型及用于故障后稳定控制的桨距角控制模型，通过包含风电场的电力系统仿真计算验证了模型的有效性及其对风电机组和电网暂态电压稳定性的贡献。仿真结果表明，当电网侧发生三相短路故障时，风电机组转子侧变频器暂态电压控制能够控制风电机组发出无功功率支持电网电压；桨距角控制能有效降低变速风电机组机械转矩，避免出现风电机组超速及电压失稳。得出结论：采用变频器暂态电压控制及桨距角控制能够改善基于双馈感应发电机的并网风电场的暂态电压稳定性，确保风电机组低电压穿越(LVRT)功能的实现及电网安全稳定。     

DESIGN OF HIGH-GAIN EXCITATION CONTROLLER OF SYNCHRONOUS GENERATOR

ABSTRACT

In this paper the design of high-gain excitation controller of a synchronous generator connected to infinite bus has been developed. For a fifth order model of a synchronous machine, it has been shown that it is necessary to have at least the first derivative term in the feedback path of high-gain excitation system. D-Decomposition technique has been applied for identifying stable domains for a range of controller parameters. Effects of controller parameters on system eigenvalues have been studied. Dynamic response of system output variables are obtained using ICL 2950 digital computer. It has been shown that the oscillations in the rotor angle and generator terminal voltage responses to a step disturbance in the turbine torque are well suppressed with armature current stabilizing signal for a wide range of operating conditions.     

MICROPROCESSOR BASED NONLINEAR EXCITATION CONTROLLER FOR SYNCHRONOUS MACHINES

ABSTRACT

The synchronous machines in power systems have the excitation systems of field winding to improve the transient stability of power systems. The synchronous machines are nonlinear systems, however, the excitation systems have been designed based on linearized systems, because the stability analysis of nonlinear systems is difficult and the generalized control method of nonlinear systems has not been developed yet.

This paper proposes a nonlinear excitation controller for synchronous machines in power systems. For the sake of simplification of the nonlinear state feedback control, this paper considers both the transient stability and the suppression of the rotor swings in transient conditions. The effect of the automatic voltage regulator (AVR) for the synchronous generator is not discussed here. This controller is designed based on Lyapunov's direct method that can directly judge the stability of nonlinear systems. The usefulness and validity of the proposed excitation controller are confirmed by numerical simulations and experiments. The microprocessor based generator excitation system that consists of a nonlinear controller, state variable detector, and PWM inverter, is constructed. The nonlinear excitation controller can improve the transient stability of synchronous machines.     

适用于弱电网的双馈风电机组新型故障穿越控制方法

弱电网下系统的电压稳定裕度较低,而风电场的故障穿越性能对系统的暂态电压稳定性有显著影响。传统的双馈风电机组故障穿越控制方法都是基于适用于强电网的定功率控制,不利于维持弱电网下的电压稳定性。提出一种适用于弱电网中双馈风电机组的新型故障穿越控制方法。这种新型控制方法基于同步控制,通过有功电流和无功电流下垂控制风电机组出口电压的角度和幅值,使双馈风电机组以可控电压源的外特性运行。该控制方法能使双馈风电机组在弱电网的对称故障和不对称故障中均提供无功和有功电流,并且能在故障清除后的重励磁暂态过程中提高系统的电压稳定性。该方法同样适用于需要在联网和孤网运行之间进行无缝切换的双馈风电机组。最后,通过双馈风电机组接入无穷大电网实际电网、孤网的仿真算例验证了该故障穿越控制方法的有效性及优越性。     

直驱风电机组次同步振荡阻尼控制方法及其适应性

由风电波动引发的次同步振荡具有振荡频率多变、涉及动态装置多、影响因素复杂等特点,现有的阻尼控制类装置难以实现有效抑制,需研究适用的附加阻尼控制方法。文中通过线性化方法推导了直驱风电机组并网系统的特征方程和传递函数,并获取了风电机组并网系统在不同工况下的频率响应特性。然后提出了基于奈奎斯特稳定判据的风电机组次同步振荡阻尼控制器的参数设计方法,以及基于粒子群优化算法的参数优化方法;结合特征值法及时域仿真法,分析了阻尼控制器对于次同步振荡的抑制作用。研究结果表明,依据前述方法设计的阻尼控制器在多种运行条件下均具有较好的适应性。     

Observer-based nonlinear control of power system using sliding mode control strategy

This paper presents a new transient stabilization with voltage regulation analysis approach of a synchronous power generator driven by steam turbine and connected to an infinite bus. The aim is to obtain high performance for the terminal voltage and the rotor speed simultaneously under a large sudden fault and a wide range of operating conditions. The methodology adopted is based on sliding mode control technique. First, a nonlinear sliding mode observer for the synchronous machine damper currents is constructed. Second, the stabilizing feedback laws for the complete ninth order model of a power system, which takes into account the stator dynamics as well as the damper effects, are developed. They are shown to be asymptotically stable in the context of Lyapunov theory. Simulation results, for a single-Machine-Infinite-Bus (SMIB) power system, are given to demonstrate the effectiveness of the proposed combined observer-controller for the transient stabilization and voltage regulation.     

STATCOM与发电机励磁非线性控制器设计

提出了一种有利于进行控制设计的STATCOM模型.采用直接反馈线性化、零动态原理,设计了STATCOM无功电流与发电机励磁非线性控制器,该控制可以同时满足发电机励磁与STATCOM装设处电压的稳定性.对单机-无穷大系统进行了数字仿真,结果表明该控制器具有很好的实用效果和优越性.     

500kV系统单相瞬时故障引起2台机组跳闸的原因分析

对一起由于500 kV系统B 相瞬时性接地故障引发发电厂2 台660 MW 机组跳闸的事件进行分析,通过分析认为：汽轮机KU保护功率变送器测量失真、KU和零功率切机保护逻辑不完善等多种因素是造成机组跳闸的主要原因,并提出整改措施.     

Sliding mode based load-frequency control in power systems

The paper presents a new discrete-time sliding mode controller for load-frequency control (LFC) in control areas (CAs) of a power system. As it uses full-state feedback it can be applied for LFC not only in CAs with thermal power plants but also in CAs with hydro power plants, in spite of their non-minimum phase behaviors. To enable full-state feedback we have proposed a state estimation method based on fast sampling of measured output variables, which are frequency, active power flow interchange and generated power from power plants engaged in LFC in the CA. The same estimation method is also used for the estimation of external disturbances in the CA, what additionally improves the overall system behavior. Design of the discrete-time sliding mode controller for LFC with desired behavior is accomplished by using a genetic algorithm. To the best of our knowledge, proposed controller outperforms any of the existing controllers in fulfilling the requirements of LFC. It was thoroughly compared to the commonly used PI controller by extensive simulation experiments on a power system with four interconnected CAs. These experiments show that the proposed controller ensures better disturbance rejection, maintains required control quality in the wider operating range, shortens the frequency’s transient response avoiding the overshoot and is more robust to uncertainties in the system.     

变风速下双馈感应发电机非线性鲁棒状态估计反馈控制

风速的强随机性与风力发电机建模的不确定性给风力发电系统的优化运行带来了极大的挑战。文中设计了一种新型非线性鲁棒状态估计反馈控制(NRSEFC),从而实现双馈感应发电机的最大功率点跟踪。首先,将风轮机的非线性、发电机参数不确定性以及随机风速的综合影响聚合为一个扰动,同时应用一个滑动模态状态扰动观测器对该扰动进行实时快速估计。随后,将该扰动估计值作为附加控制分量加入状态估计反馈控制中进行在线完全补偿。NRSEFC兼具状态反馈线性控制的结构简单、可靠性高以及非线性鲁棒控制的控制全局一致性和鲁棒性强等双方优点,不依赖于双馈感应发电机系统精确模型且仅需测量转子角速度和无功功率两个状态量。基于阶跃风速、随机风速、发电机参数测量误差以及机端电压跌落4个算例的仿真结果验证了NRSEFC的有效性和鲁棒性。最后,基于dSpace的硬件在环实验验证了所提算法的实际应用性能。