Robust nonlinear controller design of wind turbine with doubly fed induction generator by using Hamiltonian energy approach

Based on Hamiltonian energy theory, this paper proposes a robust nonlinear controller for the wind turbine with doubly fed induction generator (DFIG), such that the closed-loop system can achieve its stability. Furthermore, in the presence of disturbances, the closed-loop system is finite-gain L2 stable by the Hamiltonian controller. The Hamiltonian energy approach provides us a physical insight and gives a new way to the controller design. The simulation results illustrate that the proposed method is effective and has its advantage.     

Dynamic performance improvement of an isolated wind turbine induction generator

A dynamic model of a variable speed stand alone wind generation system is developed. The transient performance of the system under variable wind gust and other disturbance conditions has been studied. It has been observed that a stand alone generator is very vulnerable to transient disturbances in the system. A variable susceptance excitation control system, installed at the generator terminal, has been shown to improve the dynamic performance of the system following transient disturbances. Additional pole-placement based PI and PID controllers in the excitation control circuit are shown to control the violently oscillating and even growing transients very effectively. The robustness of the proposed controller has been tested for various disturbances and also for a range of operation.     

低风速风力机最大风能追踪的互补滑模控制

针对风力机系统在最大功率点跟踪(MPPT)阶段易受风速等不确定因素的影响,为了进一步提高风力机的风能捕获效率,本文在滑模控制的基础上提出了一种互补滑模控制方法.首先,建立了含有干扰项的风力机系统的线性化模型,采用广义滑模面与互补滑模面相结合的方法设计了互补滑模控制器,并在理论上证明了此控制方法能够有效保证风力机转速跟踪误差的收敛性,且能提高转速跟踪精度.其次,采用风力机专业仿真软件FAST对美国可再生能源实验室(NREL)的600 kW风力机进行了仿真实验,结果表明本文所提出的控制方法不但能提高风力机的风能捕获效率,而且能有效减小转速跟踪误差.最后,将本文所提方法与现有常见的几种控制方法相比较发现:风力机系统在互补滑模控制策略下,具有更高的风能捕获效率和更小的转速跟踪误差.     

Real-time economic nonlinear model predictive control for wind turbine control

Nonlinear model predictive control (NMPC) is a strong candidate to handle the control challenges emerging in the modern wind energy industry. Recent research suggested that wind turbine (WT) control based on economic NMPC (ENMPC) can improve the closed-loop performance and simplify the task of controller design when compared to a classical NMPC approach. This paper establishes a formal relationship between the ENMPC controller and the classic NMPC approach, and compares empirically their closed-loop nominal behaviour and performance. The robustness of the performance is assessed for an inaccurate modelling of the tower fore-aft main frequency. Additionally, though a perfect wind preview is assumed here, the effect of having a limited horizon of preview of the wind speed via the LIght Detection And Ranging (LIDAR) sensor is investigated. Finally, this paper provides new algorithmic solutions for deploying ENMPC for WT control, and report improved computational times.     

Gain-scheduling control of a floating offshore wind turbine above rated wind speed

This paper presents an application of gain-scheduling(GS) control techniques to a floating offshore wind turbine on a barge platform for above rated wind speed cases. Special emphasis is placed on the dynamics variation of the wind turbine system caused by plant nonlinearity with respect to wind speed. The turbine system with the dynamics variation is represented by a linear parameter-varying(LPV) model, which is derived by interpolating linearized models at various operating wind speeds. To achieve control objectives of regulating power capture and minimizing platform motions, both linear quadratic regulator(LQR) GS and LPV GS controller design techniques are explored. The designed controllers are evaluated in simulations with the NREL 5 MW wind turbine model, and compared with the baseline proportional-integral(PI) GS controller and non-GS controllers. The simulation results demonstrate the performance superiority of LQR GS and LPV GS controllers, as well as the performance trade-off between power regulation and platform movement reduction.     

带有速度观测器的风力发电系统风能捕获控制

为了最大化捕获风能和省去安装机械传感器的花费,提出了基于直接转矩控制理论框架的速度观测器风能捕获控制策略。这个策略能有效克服系统参数变化和风速波动不确定性的影响,实现风速跟踪控制。以2 MW直驱永磁风力发电机组作为研究对象,进行了仿真实验研究。结果表明,提出的控制策略可以实现快速风速跟踪和准确地估计转速,且对于风速变化的未知干扰具有较强的鲁棒性。     

Output feedback control of wind energy conversion system involving a doubly fed induction generator

This paper deals with the problem of controlling a wind energy conversion system (WECS) based on the doubly fed induction generator (DFIG), by IGBT‐based back‐to‐back rectifier‐inverter. The goal of control is to maximize wind energy extraction letting the wind turbine rotor operate in a variable‐speed mode. Interestingly, the present study features the achievement of the above energetic goal without resorting to sensors for wind velocity. The control strategy involves: (i) an output feedback non‐linear regulator designed by the backstepping technique and based on the use of a high gain observer; (ii) a sensorless online reference‐speed optimizer designed using the turbine power characteristic to achieve the maximum power point tracking (MPPT) requirement. It is formally shown that the proposed controller actually meets its control objectives. This theoretical result is confirmed by several simulations.     

Passivity-based control for variable speed constant frequency operation of a DFIG wind turbine

A standard passivity based control for a double fed induction generator of a wind turbine is presented. The control problem is posed as a variable speed constant frequency operation with the aim to maximise the generated electric power. The controller is designed in such a way that the dual control objective, unity power factor in the stator side and speed tracking in the mechanical port, are satisfied guaranteeing internal stability. The proposed scheme is the first attempt to approach the speed tracking operation from the energy dissipation (passivity) perspective. Simulation results show good performance of the control scheme for wind speeds in different operating regimes.     

Energy efficient control of a stand-alone wind energy conversion system with AC current harmonics compensation

This paper presents a new energy-efficient control strategy for a variable-speed wind energy conversion system (WECS). The considered WECS is designed for dc load supply and battery charging in stand-alone applications. The batteries are charged through a three-phase full-bridge power converter. The WECS contains a vector-controlled self-excited induction generator (SEIG) coupled to a wind turbine (WT) for electric power generation on the ac side. The control algorithm proposed in this paper includes three separate optimizations: two fuzzy-logic-based optimizations, which ensure that maximum energy is extracted from both the WT and the SEIG, respectively, at all operating conditions, and also the optimization of phase current harmonics through adaptive hysteresis control. In addition, a recently developed algorithm for real-time loss calculation of a hysteresis-driven power converter is utilized to quantitatively assess the power converter losses with respect to different hysteresis bandwidth settings. The performance of the proposed control algorithm is experimentally evaluated and compared with two competing algorithms which do not involve current harmonics compensation, whereas one of them also does not involve optimization of the SEIG output power. This enables evaluation of the gain in system performance due to the introduced optimizations. The evaluation and comparison are made over a wide range of wind speeds, both in steady state and under transient conditions, by using a 1.5 kW experimental setup with the DS1103 controller board (dSPACE).     

一类不确定变速风力涡轮机系统的实际跟踪控制

本文研究一类不确定变速风力涡轮机系统的实际跟踪控制问题. 与现有文献对系统不确定性和参考信号的严格限制(系统参数已知, 扰动光滑或上界已知, 参考信号二阶可导)不同, 本文允许系统参数全部未知, 扰动不必可导且上界不必已知, 参考信号仅需一阶可导, 因此传统控制设计方法无效. 为此, 本文首先给出误差系统, 将原系统的跟踪控制问题转化为误差系统的镇定控制问题. 然后, 对误差系统选择适当的李雅普诺夫函数, 将自适应动态补偿技术融入反推控制设计框架, 给出自适应状态反馈控制器显示形式. 性能分析表明该控制器保证闭环系统所有信号有界且转子转速实际跟踪到期望转速, 即在某个时刻之后到达并保持在期望转速的任意给定邻域内. 值得指出的是, 所设计的控制器仅依赖于参考信号本身而不依赖其导数, 因此降低了相关文献对参考信号可量测性的限制. 最后, 仿真实验验证理论结果的有效性.     

A rotor speed estimation algorithm in variable speed permanent magnet synchronous generator wind energy conversion system

A rotor speed estimation algorithm in a direct vector controlled permanent magnet synchronous generator wind energy conversion system is proposed. The proposed method is based on a simple equation obtained from the flux model of the machine and contains only stator flux and current. Constant gain recursive least squares estimator is used for implementing the speed estimation algorithm. Rotor position information used for coordinate transformation is computed using the estimated speed. Stator flux information required by the speed estimator is obtained using the stator voltage equation by implementing a programmable low pass filter. The estimated speed is used as the feedback signal for the speed control loop of the vector controlled machine side converter control system whose command speed is obtained from a wind speed sensorless maximum power point tracking controller, thus, we obtain a complete rotor speed and wind speed sensorless permanent magnet synchronous generator wind energy conversion system. Simulation is carried out to validate the performance of the proposed method. Copyright © 2012 John Wiley & Sons, Ltd.     

双馈感应风力发电机实现LVRT控制策略研究

根据最新的风电场接入电网规定,在电网发生故障情况下风力发电机组应能保持与电网的连接。电网电压跌落是电网故障常见的形式之一,所以如何提高双馈感应风力发电机组低电压穿越能力成为了当今风电技术的研究热点。本文根据低电压穿越技术的基本原则,通过改进转子侧的控制策略和增加保护电路的方案来实现低电压穿越技术。通过仿真研究表明,改进的控制策略可以有效的抑制转子侧过电流,能够有效的提高双馈感应风力发电机在故障期间的低电压穿越能力。     

Data-driven and adaptive control applications to a wind turbine benchmark model

Wind turbines are complex dynamic systems forced by stochastic wind disturbances, as well as gravitational, centrifugal, and gyroscopic loads. Since their aerodynamics are nonlinear, wind turbine modelling is thus challenging. Moreover, accurate models should contain many degrees of freedom to capture the most important dynamic effects. Therefore, the design of control algorithms for wind turbines should account for these complexities. However, these algorithms must capture the most important turbine dynamics without being too complex and unwieldy. The main purpose of this study is thus to give two examples of viable and practical designs of control schemes with application to a wind turbine prototype model. Extensive simulations on the benchmark process and Monte-Carlo analysis are the tools for assessing experimentally the main features of the proposed control schemes, in the presence of modelling and measurement errors. These developed control methods are also compared with other different approaches, in order to evaluate advantages and drawbacks of the considered solutions. Finally, Hardware-In-the-Loop simulations serve to highlight the potential application of the proposed control strategies to real wind turbines.     

Flicker mitigation in a doubly fed induction generator wind turbine system

This paper describes a doubly fed induction generator (DFIG) control for wind energy generation. The DFIG model is established and the adopted control strategies for machine side and grid side converters are described. Flicker phenomenon is defined and its emission of variable speed wind turbine with DFIG during continuous operation is studied. Calculation of flicker severity is evaluated using flickermeter. Appropriate vector power control of the machine side converter is proposed and applied to achieve flicker mitigation.     

Modeling and robust control of a twin wind turbines structure

The control of a new structure of twin wind turbines (TWT) is presented in this paper. This new concept includes two identical wind turbines ridden on the same tower, which can pivot face the wind with no additional actuator. The motion of the arms carrying the TWT is free. The control law based on sliding mode controller is designed to track the maximum power, by controlling the rotor speed of the TWT and the yaw rotation but without yaw actuator. Finally, performances of the proposed control strategy are compared to standard proportional integral controller, for several scenarios (time varying direction or magnitude of the wind, error on the inertia of the system, …).     

A control strategy for variable-speed variable-pitch wind turbines within the regions of partial- and full-load operation without wind speed feedback

In this paper, the control of a variable-speed variable-pitch wind turbine in the whole wind speed range is addressed, without any feedback measurement of wind speed. In addition to an aerodynamic torque observer able to ensure the tracking of the maximum delivered power in the partial-load region, a novel wind speed observer is proposed for power regulation in the full-load region, along with a sliding surface ensuring finite-time set-point stabilization of the speed tracking error. The proposed control solution has been validated on the National Renewable Energy Laboratory 5-MW three-blade wind turbine model using the recognized high-fidelity simulation tool FAST.     

Robust analysis and control for a class of uncertain nonlinear discrete-time systems

This paper deals with the problem of robust analysis and control of a class of nonlinear discrete-time systems with (constant) uncertain parameters. For the analysis problem we use a polynomial Lyapunov function and we generalize, for nonlinear systems, the “extended stability” notion proposed by Oliveira et al. (1999) in the context of linear discrete-time uncertain systems. As a result, we propose an LMI optimization problem to maximize an estimate of the domain of attraction, and also extend this approach to the synthesis problem by considering parameter-dependent Lyapunov functions and nonlinear multipliers. Numerical examples illustrate the approach and show its potential for solving analysis and control problems of nonlinear discrete-time systems.     

双馈型变速恒频风力发电系统的鲁棒控制

研究了双馈变速恒频风力发电系统的鲁棒控制问题. 采用定子磁场定向的矢量变换技术, 建立了系统非线性数学描述, 利用非线性鲁棒控制技术, 设计了能实现发电机输出有功功率和无功功率鲁棒解耦控制, 同时具有鲁棒干扰抑制作用的转子励磁控制器. 理论分析和仿真结果均表明, 所设计的控制器可以保证在风速变化、系统参数不确定性和外部干扰的情况下, 风力发电系统仍能安全可靠地最大获取风能, 并且输出恒频恒压的电量.     

Robust adaptive control for uncertain nonlinear systems with unknown control directions and actuator nonlinearity

A robust adaptive control scheme is proposed for a class of uncertain nonlinear systems in strict feedback form with both unknown control directions and non-symmetric dead-zone nonlinearity based on backstepping design.The conditions that the dead-zone slopes and the boundaries are equal and symmetric are removed by simplifying nonlinear dead-zone input model,the assumption that the priori knowledge of the control directions to be known is eliminated by utilizing Nussbaum-type gain technique and neural networks(NN) approximation capability.The possible controller singularity problem and the effect of dead-zone input nonlinearity are avoided perfectly by combining integral Lyapunov design with sliding mode control strategy.All the signals in the closed-loop system are guaranteed to be semi-globally uniformly ultimately bounded and the tracking error of the system is proven to be converged to a small neighborhood of the origin.Simulation results demonstrate the effectiveness of the proposed control scheme.     

Robust control for nonlinear systems with structured 2-gain bounded uncertainty

This paper focuses on the problem of robust control design for uncertain nonlinear systems with ₂-gain bounded dynamic uncertainty and periodically time-varying memoryless uncertainty. The robust performance problem is solved via nonlinear ^∞ control with scaling factors. It is shown that the scaling factors can be functions of state variables in contrast with linear robust control.