Load analysis of hydraulic‐pneumatic flywheel configurations integrated in a wind turbine rotor

In this paper, the impact on the mechanical loads of a wind turbine due to a previously proposed hydraulic‐pneumatic flywheel system is analysed. Load simulations are performed for the National Renewable Energy Laboratory (NREL) 5‐MW wind turbine using fatigue, aerodynamics, structures, and turbulence (FAST). It is discussed why FAST is applied although it cannot simulate variable rotor inertia. Several flywheel configurations, which increase the rotor inertia of the 5‐MW wind turbine by 15%, are implemented in the 61.5‐m rotor blade. Load simulations are performed twice for each configuration: Firstly, the flywheel system is discharged, and secondly, the flywheel is charged. The change in ultimate and fatigue loads on the tower, the low speed shaft, and the rotor blades is juxtaposed for all flywheel configurations. As the blades are mainly affected by the flywheel system, the increase in ultimate and fatigue loads of the blade is evaluated. Simulation results show that the initial design of the flywheel system causes the lowest impact on the mechanical loads of the rotor blades although this configuration is the heaviest.     

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.     

Virtual inertia for variable speed wind turbines

Inertia provision for frequency control is among the ancillary services that different national grid codes will likely require to be provided by future wind turbines. The aim of this paper is analysing how the inertia response support from a variable speed wind turbine (VSWT) to the primary frequency control of a power system can be enhanced. Unlike fixed speed wind turbines, VSWTs do not inherently contribute to system inertia, as they are decoupled from the power system through electronic converters. Emphasis in this paper is on how to emulate VSWTs inertia using control of the power electronic converter and on its impact on the primary frequency response of a power system. An additional control for the power electronics is implemented to give VSWTs a virtual inertia, referring to the kinetic energy stored in the rotating masses, which can be released initially to support the system's inertia. A simple Matlab/Simulink model and control of a VSWT and of a generic power system are developed to analyse the primary frequency response following different generation losses in a system comprising VSWTs provided with virtual inertia. The possibility of substituting a 50% share of conventional power with wind is also assessed and investigated. The intrinsic problems related to the implementation of virtual inertia are illustrated, addressing their origin in the action of pitch and power control. A solution is proposed, which aims at obtaining the same response as for the system with only conventional generation. The range of wind speeds near the power limitation zone seems to be the most critical from a primary response point of view. The theoretical reasons behind this are elucidated in the paper. Copyright © 2012 John Wiley & Sons, Ltd.     

考虑直流侧电容存储能量的风电机组虚拟惯性控制策略

文章在传统转子动能虚拟惯性控制策略基础上,提出了一种考虑直流侧电容存储能量的风电机组虚拟惯性控制策略。该策略在建立转子动能和系统频率偏差关系的基础上,建立了风电变流器直流侧电容电压和系统频率偏差的函数关系,在频率事件下能够充分利用电容所存储的能量来增强电网的惯性,提高电网的频率调节能力。最后,通过PSCAD/EMTDC仿真验证了所提控制策略的有效性。     

Power smoothing control for wind farms using flywheel based energy storage

在风电场增设飞轮储能装置可以有效地平抑风电场的功率波动,提高电网的风电接纳能力。本文采用在风电场出口母线处接入飞轮储能装置,通过分析风电系统和飞轮储能装置的特性,提出了一种基于瞬时功率理论的有功功率平滑控制策略。在传统低通滤波器的基础上,增加高通滤波器,对网侧有功功率的快速扰动成分进行处理,最终通过低通、高通滤波器来获得飞轮装置的补偿功率,达到对网侧有功功率波动进行抑制的目的。最后利用Matlab/Simulink进行仿真验证,仿真结果表明,文中的控制策略可以较好地实现电网侧有功功率的平滑控制,减小有功功率波动。     

Adjustment of wind farm power output through flexible turbine operation using wind farm control

When the installed capacity of wind power becomes high, the power generated by wind farms can no longer simply be that dictated by the wind speed. With sufficiently high penetration, it will be necessary for wind farms to provide assistance with supply‐demand matching. The work presented here introduces a wind farm controller that regulates the power generated by the wind farm to match the grid requirements by causing the power generated by each turbine to be adjusted. Further, benefits include fast response to reach the wind farm power demanded, flexibility, little fluctuation in the wind farm power output and provision of synthetic inertia. Copyright © 2015 John Wiley & Sons, Ltd.     

A new control methodology of wind turbine generators for frequency control of power system in isolated island

A wind turbine generator (WTG) system's output is not constant and fluctuates depending on wind conditions. Fluctuating power causes frequency deviations and adverse effects to an isolated power system when large output power from WTG systems is penetrated in the power system. This paper presents an output power control methodology of a WTG for frequency control using a load power estimator. The load power is estimated by a disturbance observer, and the output power command of the WTG is determined according to the estimated load. Besides, the WTG can also be controlled during wind turbulence since the output power command is determined by considering wind conditions. The reduction of the power system frequency deviation by using the WTG can be achieved by the proposed method. The effectiveness of the proposed method is validated by numerical simulations. Copyright © 2010 John Wiley & Sons, Ltd.     

风力发电机用飞轮储能智能控制系统研究

针对在风力发电机上具有广泛应用前景的飞轮储能技术,设计了储能系统的矢量控制器硬件电路及实验平台、电机控制系统的主电路和驱动电路、DSP主控板、电压及电流信号的采集系统等。基于矢量控制原理,进行了电机控制系统仿真研究。仿真结果表明,该系统能够精确地实现对电机速度的跟踪。在飞轮储能与风力发电模拟系统的试验中,为了验证控制系统的响应速度及稳态精度,利用交流电网对飞轮充电,有效地实现了飞轮与电机的耦合及飞轮能量的快速存储和释放。     

Dynamic wind turbine output power reduction under varying wind speed conditions due to inertia

The inertia of wind turbines causes a reduction in their output power due to their inability to operate at the turbine maximum co‐efficient of performance point under dynamic wind conditions. In this paper, this dynamic power reduction is studied analytically and using simulations, assuming that a steady‐state optimal torque control strategy is used. The concepts of the natural and actual turbine time‐constant are introduced, and typical values for these parameters are examined. It is shown that for the typical turbine co‐efficient of performance curve used, the average turbine speed can be assumed to be determined by the average wind speed. With this assumption, analytical expressions for the power reduction with infinite and then finite turbine inertia are determined for sine‐wave wind speed variations. The results are then generalized for arbitrary wind speed profiles. A numerical wind turbine system simulation model is used to validate the analytical results for step and sine‐wave wind speed variations. Finally, it is used with real wind speed data to compare with the analytical predictions. Copyright © 2012 John Wiley & Sons, Ltd.     

Z40风机控制系统国产化改造设计

系统介绍了风机控制系统国产化致造的基本思路、总体结构、系统功能以及设备选型等。     

Analysis of light detection and ranging wind speed measurements for wind turbine control

Light detection and ranging (LIDAR) systems are able to measure the speed of incoming wind before it reaches a wind turbine rotor. These preview wind measurements can be used in feedforward control systems designed to reduce turbine structural loads. However, the degree to which such preview‐based control techniques can reduce loads by reacting to turbulence depends on how accurately the incoming wind field can be measured. This study examines the accuracy of different measurement scenarios that rely on coherent continuous‐wave or pulsed Doppler LIDAR systems, in terms of root‐mean‐square measurement error, to determine their applicability to feedforward control. In particular, the impacts of measurement range, angular offset of the LIDAR beam from the wind direction, and measurement noise are studied for various wind conditions. A realistic simulation case involving a scanning LIDAR unit mounted in the spinner of a MW‐scale wind turbine is studied in depth, with emphasis on preview distances that provide minimum measurement error for a specific scan radius. Measurement error is analyzed for LIDAR‐based estimates of point wind speeds at the rotor as well as spanwise averaged blade effective wind speeds. The impact of turbulence structures with high coherent turbulent kinetic energy on measurement error is discussed as well. Copyright © 2013 John Wiley & Sons, Ltd.     

Design of a wind turbine rotor for maximum aerodynamic efficiency

The design of a three‐bladed wind turbine rotor is described, where the main focus has been highest possible mechanical power coefficient, CP, at a single operational condition. Structural, as well as off‐design, issues are not considered, leading to a purely theoretical design for investigating maximum aerodynamic efficiency. The rotor is designed assuming constant induction for most of the blade span, but near the tip region, a constant load is assumed instead. The rotor design is obtained using an actuator disc model, and is subsequently verified using both a free‐wake lifting line method and a full three‐dimensional Navier–Stokes solver. Excellent agreement is obtained using the three models. Global CP reaches a value of slightly above 0.51, while global thrust coefficient CT is 0.87. The local power coefficient C_p increases to slightly above the Betz limit on the inner part of the rotor; the local thrust coefficient C_t increases to a value above 1.1. This agrees well with the theory of de Vries, which states that including the effect of the low pressure behind the centre of the rotor stemming from the increased rotation, both C_p and C_t will increase towards the root. Towards the tip, both C_p and C_t decrease due to tip corrections as well as drag. Copyright © 2008 John Wiley & Sons, Ltd.     

小型风力机风轮主动侧偏机构试验研究

根据输出的功率信号,对尾翼侧偏角度进行调节,可以在保证主动侧偏型小型风力发电机稳定安全运行的基础上,实现风能最大利用.通过实验得出不同侧偏角下风轮功率的输出,然后根据模拟输出功率信号,测试在不同工况下,主动侧偏机构动作的正确性和可行性,为整机试验做好前期准备工作.     

A spinner‐integrated wind lidar for enhanced wind turbine control

A field test with a continuous wave wind lidar (ZephIR) installed in the rotating spinner of a wind turbine for unimpeded preview measurements of the upwind approaching wind conditions is described. The experimental setup with the wind lidar on the tip of the rotating spinner of a large 80 m rotor diameter, 59 m hub height 2.3 MW wind turbine (Vestas NM80), located at Tjæreborg Enge in western Denmark is presented. Preview wind data at two selected upwind measurement distances, acquired during two measurement periods of different wind speed and atmospheric stability conditions, are analyzed. The lidar‐measured speed, shear and direction of the wind field previewed in front of the turbine are compared with reference measurements from an adjacent met mast and also with the speed and direction measurements on top of the nacelle behind the rotor plane used by the wind turbine itself. Yaw alignment of the wind turbine based on the spinner lidar measurements is compared with wind direction measurements from both the nearby reference met mast and the turbine's own yaw alignment wind vane. Furthermore, the ability to detect vertical wind shear and vertical direction veer in the inflow, through the analysis of the spinner lidar data, is investigated. Finally, the potential for enhancing turbine control and performance based on wind lidar preview measurements in combination with feed‐forward enabled turbine controllers is discussed. Copyright © 2012 John Wiley & Sons, Ltd.     

Review of flywheel energy storage systems for wind power applications

风力发电可以解决能源短缺和环境污染等问题,但由于风速随机性和间歇性的特点导致风电输出电压、功率和频率存在较大波动,因此风电的大规模并网会对现有电网的稳定运行造成不利影响。飞轮储能是一种高效无污染的储能技术,而且通过合理的控制策略和控制设备可实现电网调频及短时间调峰以解决大规模风电并网带来的问题。本文主要介绍了飞轮储能在风力发电领域的应用背景、飞轮储能的结构原理和目前国内外在飞轮储能控制策略方向的研究进展。     

新型飞轮储能电池在独立运行式风力发电系统中的应用研究

本文提出了一种采用飞轮储能电池来充当能量储存器和电能质量调节器的独立运行式风力发电 系统,它由新型飞轮储能电池、风力发电机系统两大部分组成。文中分析了飞轮储能电池的储能和调节 电能质量的作用,详细分析了直流侧电压的调节方法,利用能量平衡原理推导出了前馈参数(iL-iG)与 定子电流iq的关系,并给出了控制方法。仿真结果证明了该系统具有优越的储能和改善电能质量的效 果。     

MPC framework for constrained wind turbine individual pitch control

The reduction of structural loads is becoming an important objective for the wind turbine control system due to the ever‐increasing specifications/demands on wind turbine rated power and related growth of turbine dimensions. Among various control algorithms that have been researched in recent years, the individual pitch control has demonstrated its effectiveness in wind turbine load reduction. Since the individual pitch control, like other load reduction algorithms, requires higher levels of actuator activity, one must take actuator constraints into account when designing the controller. This paper presents a method for the inclusion of such constraints into a predictive wind turbine controller. It is shown that the direct inclusion of constraints would result in a control problem that is nonconvex and difficult to solve. Therefore, a modification of the constraints is proposed that ensures the convexity of the control problem. Simulation results show that the developed predictive control algorithm achieves individual pitch control objectives while satisfying all imposed constraints.     

Dynamic characteristics and enhanced performance of a novel wind turbine rotor analyzed via experiments and numerical simulation

The enormous demand for large wind turbine rotors has led to a need to develop high‐performance and reliable wind turbine rotors. The flexibility of the huge blade was a challenge in creating a balanced design with regard to dynamic behavior, mass, and power output. To enhance the wind turbine rotor, a newly designed wind turbine system with a supporting rod and damper was proposed and investigated. A scaled blade was experimentally tested, with the results indicating an increase in both frequency and damping of the system. Through the use of a self‐coded numerical model, the correlations between the design constraints and the dynamic behavior, tip displacement, and additional mass of the rotor were demonstrated. This showed that the novel rotor has some preferable characteristics in both static and dynamic aspects. In particular, this blade is stiffer and has a smaller tip displacement compared with a traditional cantilevered blade. These characteristics enabled the effective application of the novel rotor to a 5‐MW wind turbine to achieve a 15.16% power output increase based on the blade element momentum theory with Prandtl correction, as well as 5.1% mass savings. Copyright © 2016 John Wiley & Sons, Ltd.     

Maximum wind power generation in a power system imposed by system inertia and primary reserve requirements

Although the technology to simulate inertia or to provide primary control in wind power generators is mature, most of them are a source of power with neither inertia nor primary reserve provision mainly because it means wind spilling. Therefore, an increasing wind power penetration means a reduction in the inertia of the system and of the primary reserve due to the substitution of conventional generation. In this paper, the maximum wind power penetration focusing on system inertia and primary reserve value is assessed. The Spanish power system is used as an example for the calculation of these values. For this purpose, real Spanish scenario data are used. Results will show that high penetrations of wind power can be achieved without risking adequate values of primary reserve or inertia of the power system even if wind power does not contribute to these items. Copyright © 2014 John Wiley & Sons, Ltd.     

Power curve control in micro wind turbine design

In this work, a micro wind turbine will be designed and built for a series of wind tunnel tests (rotor dynamics and Wind Turbine (WT) start-up velocity). Its design stems from an original numerical code, developed by the authors, based on the Blade Element Momentum (BEM) Theory.