SSCI mitigation of grid‐connected DFIG wind turbines with fractional‐order sliding mode controller

To mitigate subsynchronous control interaction (SSCI) in doubly fed induction generator (DFIG)‐based wind farm, this paper proposes a robust controller for rotor‐side converter (RSC) using fractional‐order sliding mode controller (FOSMC). The proposed FOSMC can improve robustness and convergence properties of the controlled system, thus achieving SSCI damping under various operating conditions. Impedance‐based analysis and time‐domain simulation are performed to check the capability of the designed FOSMC as compared with conventional sliding mode control (SMC) and subsynchronous damping control (SSDC). Simulation results demonstrate that FOSMC can mitigate SSCI within shorter time and effectively reduce the fluctuation range of system transient responses under various operating conditions of wind speeds and compensation levels. Moreover, FOSMC also improves system robustness against parameter uncertainties and external disturbances, which is important for safe operation of realistic wind farms.     

Frequency support capability of variable speed wind turbine based on electromagnetic coupler

In the variable speed wind turbine based on electromagnetic coupler (WT-EMC), a synchronous generator is directly coupled with grid. So like conventional power plants WT-EMC is able to support grid frequency inherently. But due to the reduced inertia of synchronous generator, its frequency support capability has to be enhanced. In this paper, the frequency support capability of WT-EMC is studied at three typical wind conditions and with two control strategies—droop control and inertial control to enhance its frequency support capability. The synchronous generator speed, more stable than the grid frequency which is the input signal for Type 3 and Type 4 wind turbine frequency support controller, is used for the calculation of WT-EMC supplementary torque command. The integrated simulation environment based on the aeroelastic code HAWC2 and software Matlab/Simulink is used to build a 2 MW WT-EMC model and study the frequency support capability of a wind farm consisting of WT-EMC.     

风力发电系统输出功率随机波动的仿真分析

针对当前风力发电系统输出功率随机波动的问题,以永磁同步风力发电机(PMSG)与直流侧储能系统(钒氧化还原电池)整合的风力发电系统为基础,进行数字仿真建模,采用MATLAB/Simulink软件对固定负载,变化风速工况;固定风速,负荷瞬变工况;风速和负荷同时变化工况;进行了仿真试验和分析。结果表明,对于采用储能技术的风电场并网功率随机波动的平抑控制,可以利用蓄电池的充放电特性,在风速变化以及负荷瞬变时进行功率平衡的调节。     

Design and laboratory test of black‐start control mode for wind turbines

In this article, an operational strategy and control concept for wind turbines (WTs) are described, which would allow them to actively contribute to black‐start events after major power system outages. The approach is based on (a) a new generator/converter control strategy implementing a so called virtual synchronous machine (VSM) and (b) a number of modifications to the superimposed WT controller allowing for operation in black‐start conditions. In order to operate stably even at very low active power levels and to cope with sudden changes in active power, due to switching of loads in the recovered grid, the rotor speed/pitch controller had to be redesigned. The extension of the operational range of the WT towards negative power, ie, power consumption, is discussed, which would allow the turbine to temporarily provide a controllable minimum load to conventional power plants until a sufficient number of consumers has been reconnected. The control system has been implemented and verified using two experimental power converters, each linked to a hardware‐in‐the‐loop (HiL) simulator of a WT and connected to a real medium‐voltage laboratory grid.     

A fuzzy control strategy for power smoothing and grid dynamic response enrichment of a grid‐connected wind energy conversion system

This paper concentrates on the output power smoothing and the grid dynamic response enhancement of a grid‐interactive MW‐class permanent magnet synchronous generator‐based wind energy conversion system (WECS). A simple fuzzy controller method is applied to improve the overall performance of the WECS. The proposed method can retrieve the storing kinetic energy from the inertia of a wind turbine, perfectly. As a result, it can ensure a proficient power smoothing of the variable speed WECS. On the other hand, the grid side inverter is controlled by the fuzzy controller. This approach can reduce the fluctuation of DC link voltage and can deliver a smooth power to the power grid. The proposed method is compared with two other methods such as the maximum power point tracking control method and the without fuzzy controller method. A simple shunt circuit also includes in the DC link circuit. Therefore, during the system fault condition, the WECS can perform a stable operation. Effectiveness of the proposed method is verified by numerical simulations. Copyright © 2013 John Wiley & Sons, Ltd.     

Transient and dynamic control of a variable speed wind turbine with synchronous generator

In this article, a controller for dynamic and transient control of a variable speed wind turbine with a full‐scale converter‐connected high‐speed synchronous generator is presented. First, the phenomenon of drive train oscillations in wind turbines with full‐scale converter‐connected generators is discussed. Based on this discussion, a controller is presented that dampens these oscillations without impacting on the power that the wind turbine injects into the grid. Since wind turbines are increasingly demanded to take over power system stabilizing and control tasks, the presented wind turbine design is further enhanced to support the grid in transient grid events. A controller is designed that allows the wind turbine to ride through transient grid faults. Since such faults often cause power system oscillations, another controller is added that enables the turbine to participate in the damping of such oscillations. It is concluded that the controllers presented keep the wind turbine stable under any operating conditions, and that they are capable of adding substantial damping to the power system. Copyright © 2007 John Wiley & Sons, Ltd.     

Modelling and control of synchronous generators for wide‐range variable‐speed wind turbines

The modelling and control of a wide‐range variable speed wind turbine based on a synchronous generator are presented. Two different methods to control the operation of the synchronous generator are investigated, i.e. load angle control and instantaneous vector control. The dynamic performance characteristics of these control strategies are evaluated and compared using three model representations of the generator: a non‐reduced order model including both stator and rotor transients, a reduced order model with stator transients neglected, and a steady‐state model that neglects generator electrical dynamics. Assessment on the performance of grid‐side controller is shown during network fault and frequency variation. A simplified wind turbine model representation is also developed and proposed for large‐scale power system studies. Simulation results in Matlab/Simulink are presented and discussed. Copyright © 2007 John Wiley & Sons, Ltd.     

A novel method for obtaining virtual inertial response of DFIG‐based wind turbines

This paper investigates virtual inertia control of doubly fed induction generator (DFIG)‐based wind turbines to provide dynamic frequency support in the event of sudden power change. The relationships among DFIGs' virtual inertia, rotor speed and network frequency variation are analysed, and a novel virtual inertia control strategy is proposed. The proposed control strategy shifts the maximum power point tracking (MPPT) curve to the virtual inertia control curves according to the frequency deviation so as to release the ‘hidden’ kinetic energy and provide dynamic frequency support to the grid. The calculation of the virtual inertia and its control curves are also presented. Compared with a PD regulator‐based inertial controller, the proposed virtual inertia control scheme not only provides fast inertial response in the event of sudden power change but also achieves a smoother recovery to the MPPT operation. A four‐machine system with 30% of wind penetration is simulated to validate the proposed control strategy. Simulation results show that DFIG‐based wind farms can provide rapid response to the frequency deviation using the proposed control strategy. Therefore, the dynamic frequency response of the power grid with high wind power penetration can be significantly improved. Copyright © 2015 John Wiley & Sons, Ltd.     

Simulating Feedback Linearization control of wind turbines using high‐order models

As wind turbines are becoming larger, wind turbine control must now encompass load control objectives as well as power and speed control to achieve a low cost of energy. Due to the inherent non‐linearities in a wind turbine system, the use of non‐linear model‐based controllers has the potential to increase control performance. A non‐linear feedback linearization controller with an Extended Kalman Filter is successfully used to control a FAST model of the controls advanced research turbine with active blade, tower and drive‐train dynamics in above rated wind conditions. The controller exhibits reductions in low speed shaft fatigue damage equivalent loads, power regulation and speed regulation when compared to a Gain Scheduled Proportional Integral controller, designed for speed regulation alone. The feedback linearization controller shows better rotor speed regulation than a Linear Quadratic Regulator (LQR) at close to rated wind speeds, but poorer rotor speed regulation at higher wind speeds. This is due to modeling inaccuracies and the addition of unmodeled dynamics during simulation. Similar performance between the feedback linearization controller and the LQR in reducing drive‐train fatigue damage and power regulation is observed. Improvements in control performance may be achieved through increasing the accuracy of the non‐linear model used for controller design. Copyright © 2009 John Wiley & Sons, Ltd.     

参与电网调频的风电机组线性变参数变桨控制策略

风电机组参与调频时其输出功率的调整将改变风电机组变桨动作的风速范围,同时由于桨距角调节气动功率的灵敏度随风况变化,使得传统PI变桨控制难以适用于风电机组参与调频时的复杂工况,出现风电机组转速振荡问题.提出一种基于线性变参数(Linear Parameter Varying,LPV)系统的风电机组变桨控制方法,对风电机组...     

Neural network controller for a permanent magnet generator applied in a wind energy conversion system

In this paper a neural network controller for achieving maximum power tracking as well as output voltage regulation, for a wind energy conversion system (WECS) employing a permanent magnet synchronous generator, is proposed. The permanent magnet generator (PMG) supplies a DC load via a bridge rectifier and two buck–boost converters. Adjusting the switching frequency of the first buck–boost converter achieves maximum power tracking. Adjusting the switching frequency of the second buck–boost converter allows output voltage regulation. The on-times of the switching devices of the two converters are supplied by the developed neural network (NN). The effect of sudden changes in wind speed, and/or in reference voltage on the performance of the NN controller are explored. Simulation results showed the possibility of achieving maximum power tracking and output voltage regulation simultaneously with the developed NN controller. The results proved also the fast response and robustness of the proposed control system.     

Modelling–based approach for digital control design for nonlinear WECS in the power system

The case has been established that the wind power plant must be treated as an integral part of the electric system, thereby constituting the wind energy conversion system. Recent advancement in size and technology of wind turbines requires sophisticated control systems to effectively optimize energy conversion and enhance grid integration. As a first step toward controller design, modelling has become a prerequisite. This paper explores controller design based on modelling the wind speed as a stochastic process, and the wind turbine as a multi‐mass system with a soft shaft linking the turbine with the doubly fed induction generator. A control strategy incorporating a linear quadratic Gaussian (LQG) that relies on state estimation for full‐state feedback is proposed to augment a linear controller for generator torque control. The control objectives are to reduce stresses on the drivetrain and to ensure operation geared toward optimal power conversion. This study focuses on above‐rated wind speeds, and the LQG's main purpose is to add damping to the drivetrain, thereby minimizing cyclic fatigue, while a pitch control mechanism prevents rotor overspeed, thereby maintaining rated power. Simulations show the efficacy of the proposed paradigm in meeting the control objectives. Copyright © 2009 John Wiley & Sons, Ltd.     

An Autonomous System Supplied Only by a Pitch-Controlled Variable-Speed Wind Turbine

This paper presents a control strategy for a variable-speed pitch-controlled wind turbine (WT) generation scheme for the supply of an autonomous system with no energy storage units. The synchronous generator includes two three-phase stator windings displaced by 30deg that are connected to the transformer load through two dc links with voltage source inverters (VSI). Following priority rules, the load is divided into steps. Each load step can be supplied by the WT when the wind speed varies between two predefined speed levels. The first goal of the WT control system is to supply the load with constant real power under constant voltage as the wind speed varies between two levels and the second is to operate smoothly interchanging the load steps when the wind speed breaks through a speed level. There are two controllers: the inverter controller that keeps the load voltage constant and the pitch controller acting on the blade's angle. Using simulation techniques, the operation of the WT system and the efficiency of the proposed control strategy are demonstrated for a wide range of wind speeds.     

Robust multi‐model control of an autonomous wind power system

This article presents a robust multi‐model control structure for a wind power system that uses a variable speed wind turbine (VSWT) driving a permanent magnet synchronous generator (PMSG) connected to a local grid. The control problem consists in maximizing the energy captured from the wind for varying wind speeds. The VSWT‐PMSG linearized model analysis reveals the resonant nature of its dynamic at points on the optimal regimes characteristic (ORC). The natural frequency of the system and the damping factor are strongly dependent on the operating point on the ORC. Under these circumstances a robust multi‐model control structure is designed. The simulation results prove the viability of the proposed control structure. Copyright © 2006 John Wiley & Sons, Ltd.     

Controller design for an induction generator driven by a variable-speed wind turbine

This paper presents the modeling, controller design and a steady-state analysis algorithm for a wind-driven induction generator system. An output feedback linear quadratic controller is designed for the static synchronous compensator (STATCOM) and the variable blade pitch in a wind energy conversion system (WECS) in order to reach the voltage and mechanical power control under both grid-connection and islanding conditions. A two-reference-frame model is proposed to decouple the STATCOM real and reactive power control loops for the output feedback controller. To ensure zero steady-state voltage errors for the output feedback controller, the integrals of load bus voltage deviation and dc-capacitor voltage deviation are employed as the additional state variables. Pole-placement technique is used to determine a proper weighting matrix for the linear quadratic controller such that satisfactory damping characteristics can be achieved for the closed-loop system. Effects of various system disturbances on the dynamic performance have been simulated, and the results reveal that the proposed controller is effective in regulating the load voltage and stabilizing the generator rotating speed for the WECS either connected with or disconnected from the power grid. In addition, proper steady-state operating points for an isolated induction generator can be determined by the proposed steady-state analysis algorithm. Constant output frequency control using the derived steady-state characteristics of the isolated induction generator is then demonstrated in this paper.     

Aggregate load-frequency control of a wind-hydro autonomous microgrid

This paper presents an aggregate load-frequency controller for an autonomous microgrid (MG) with wind and hydro renewable energy sources. A micro-hydro power plant with a synchronous generator (SG) and a wind power plant with an induction generator (IG) supply the MG. Both generators directly feed power into the grid without the use of additional power electronics interfaces, thus the solution becoming robust, reliable and cost-effective. An original electronic load controller (ELC) regulates the MG frequency by a centralized load-frequency control method, which is based on a combination of smart load (SL) and battery energy storage system (BESS). SL and BESS provides the active power balance for various events that such systems encounter in real situations, both in cases of energy excess production and energy shortage. Moreover, the proposed ELC includes an ancillary function to compensate the power unbalance produced by the uneven distribution of the single-phase loads on the MG phases, without the use of extra hardware components. A laboratory-scale prototype is used for experimentally assessment of the proposed solutions. The experimental results emphasize the effectiveness of the ELC while also showing its limitations.     

计及风电场与负荷惯性响应的电力系统惯性时间常数测量

大量风电接入导致电力系统惯量减少、频率稳定性变差.为评估电力系统频率稳定性,将电力系统的惯性划分为同步发电机、风电场和负荷提供的三种不同类别的惯性,通过摇摆方程建立目标函数,应用粒子群算法求解风电场和同步发电机惯性时间常数,为提高粒子群算法计算结果的稳定性引入绝对中位差算法,在Matlab/Simulink中搭建含有风...     

Model‐based control addition to prescribe DFIG wind turbine fast frequency response

This paper investigates the physical capability of double‐fed induction generator (DFIG) wind turbines for inertial support of frequency response. Frequency stability is modeled using the DFIG electromechanical and generator controller dynamics, and a destabilizing effect is demonstrated in low‐inertia systems. To improve response, a synchronous reference frame DFIG controller is proposed that acts by following low‐frequency grid dynamics and adds a fast acting proportional plus integral (PI)‐controlled frequency‐responsive component to existing qd current commands. The proposed controller is derived in a straightforward manner using only the DFIG dynamic equations and is designed using pole/zero placement techniques. Laboratory experiments using a micro‐scale DFIG wind turbine with hub‐emulating flywheel prove better capability for transient frequency regulation even under extreme load change. The result is a DFIG controller that balances the appearance of transients in electrical and mechanical systems. Value is achieved in providing immediate continuous inertial response to support load change. The proposed frequency response can improve the use of existing physical inertia from wind turbines.     

含风电的多域互联电力系统负荷频率控制方法

为确保风机参与调整系统负荷频率,建立了三区域含风力发电的互联电力系统负荷频率控制模型;同时,为抑制整个系统内部参数的变化、风能波动及负荷扰动所造成的负荷频率波动,又设计出一个分散的滑模控制器并用于仿真分析,当整个系统在进入滑动模态后,对外界的参数变化具有时不变性。仿真结果表明,所设计的滑模控制器比传统的控制器响应更快、超调量小,有效抑制了负荷频率波动,且当考虑发电机变化率约束条件时,所设计的滑模控制器仍能有效控制系统稳定。     

Anti‐windup linear parameter‐varying control of pitch actuators in wind turbines

Operation of wind turbines in the full‐load region mandates that the produced power is kept at a rated value to minimize structural loads and thereby reduce fatigue damage. This is usually achieved by pitching the rotor blades in order to limit the aerodynamic torque in high wind speeds. The pitch actuators usually present a hard constraint in terms of the amplitude and rate of saturation. In this paper, we propose a method to address pitch actuator amplitude and rate saturation by designing anti‐windup controllers in the linear parameter‐varying framework. The proposed design method guarantees the closed‐loop system stability and a prescribed level of performance while it decreases the pitch activity for regulating the generated power to the nominal power during sudden wind gusts. The anti‐windup controller designed to minimize the norm of the closed‐loop system is gain‐scheduled on the basis of the operating condition of the turbine, as well as the states of amplitude and rate saturation of the pitch actuator. The effectiveness of the proposed control design method is demonstrated using high‐fidelity aeroelastic dynamic simulation tools. Copyright © 2013 John Wiley & Sons, Ltd.