Output power dispatch control for a wind farm in a small power system

Nowadays, a wind turbine generator (WTG) is required to provide control capabilities as the output power of WTG fluctuates. Under this scenario, this paper proposes an output power control method of a wind farm (WF) connected to a small power system using pitch angle control. In this control approach, the WF output power control is achieved by two control levels: central and local. In the central control, the WF output power command is determined by considering the frequency deviations and wind speeds using a fuzzy function. Then, the local output power commands for each of the WTGs are based on the proposed dispatch control. In the proposed dispatch control, the output commands of each WTG are determined by considering wind conditions for each of the WTGs. The simulation results by using an actual detailed model for the wind power system show the effectiveness of the proposed method. Copyright © 2010 John Wiley & Sons, Ltd.     

An integrated control method for a wind farm to reduce frequency deviations in a small power system

Output power of wind turbine generator (WTG) is not constant and fluctuates due to wind speed changes. To reduce the adverse effects of the power system introducing WTGs, there are several published reports on output power control of WTGs detailing various researches based on pitch angle control, variable speed wind turbines, energy storage systems, and so on. In this context, this paper presents an integrated control method for a WF to reduce frequency deviations in a small power system. In this study, the WF achieves the frequency control with two control schemes: load estimation and short-term ahead wind speed prediction. For load estimation in the small power system, a minimal-order observer is used as disturbance observer. The estimated load is utilized to determine the output power command of the WF. To regulate the output power command of the WF according to wind speed changing, short-term ahead wind speed is predicted by using least-squares method. The predicted wind speed adjusts the output power command of the WF as a multiplying factor with fuzzy reasoning. By means of the proposed method, the WF can operate according to the wind and load conditions. In the WF system, each output power of the WTGs is controlled by regulating each pitch angle. For increasing acquisition power of the WF, a dispatch control method also is proposed. In the pitch angle control system of each WTG, generalized predictive control (GPC) is applied to enhance the control performance. Effectiveness of the proposed method is verified by the numerical simulations.     

Output power control for large wind power penetration in small power system

Nowadays, wind turbine generator (WTG) is increasingly required to provide control capabilities regarding output power. Under this scenario, this paper proposes an output power control of WTG using pitch angle control connected to small power systems. By means of the proposed method, output power control of WTG considering states of power system becomes possible, and in general both conflicting objectives of output power leveling and acquisition power increase are achieved. In this control approach, WTG is given output power command by fuzzy reasoning which has three inputs for average wind speed, variance of wind speed, and absolute average of frequency deviation. Since fuzzy reasoning is used, it is possible to define output power command corresponding to wind speed condition and changing capacity of power system momentarily. Moreover, high performance pitch angle control based on output power command is achieved by generalized predictive control (GPC). The simulation results by using actual detailed model for wind power system show the effectiveness of the proposed method.     

双时间尺度下风电主导的微电网频率控制方法

文章提出了利用风电输出特征对微电网进行频率控制的方法.该方法首先对电网一、二次调频的双时间尺度特征进行了阐述,分析了风机虚拟惯性与桨距角调整两种输出控制方法,并讨论了此两种方式在时间尺度上与电网一、二次调频的对应关系.在此基础上,设计了风机虚拟惯性参与系统一次调频,桨距角调整参与二次调频的混合频率控制方法.最后以风、光...     

Distributed control system for frequency control in a isolated wind system

High wind penetration wind diesel hybrid systems (WDHS) have three modes of operation: diesel only (DO), wind diesel (WD) and wind only (WO). The control requirements for frequency control in WO mode are analysed and a distributed control system (DCS) is proposed for this frequency control, describing the actuation of its sensor and actuator nodes. A power system for WO mode consisting of a wind turbine generator (WTG), a synchronous machine (SM), the consumer load, a battery based energy storage system (ESS) and a discrete dump load (DL) along with the associated DCS have been simulated. By means of a 400 Hz reference power message that establishes the active power necessary for frequency regulation and a prescribed active power sharing between the ESS and DL actuators, graphs for frequency, voltage and active powers for consumer load and wind speed changes are presented. The results of the simulation show maximum settling times and frequency per unit variation of 1.5 s and 0.16% respectively, for the previous input changes. The DCS solution presented could constitute a proposal for the standardization of the control for WO mode in high wind penetration WDHS which rely on a SM to generate the voltage waveform in that mode.     

A flywheel in a wind turbine rotor for inertia control

In this paper, a flywheel energy storage that is an integral part of a wind turbine rotor is proposed. The rotor blades of a wind turbine are equipped with internal weights, which increase the inertia of the rotor. The inertia of this flywheel can be controlled by varying the position of the weights, i.e. by positioning them closer to the center of rotation (closer to the hub) or closer to the tip of the blades. The simulation model used in this study is introduced briefly. The equation system of the flywheel is set up. Finally, simulations of different scenarios show the performance of this controllable flywheel. The conclusion is that the proposed system can mitigate transients in the power output of wind turbines. Hence, it can support the frequency control in a power system by contributing to the power system inertia. © 2014 The Authors. Wind Energy published by John Wiley & Sons, Ltd.     

Output power leveling of wind turbine Generator for all operating regions by pitch angle control

Wind energy is not constant and windmill output is proportional to the cube of wind speed, which causes the generated power of wind turbine generators (WTGs) to fluctuate. In order to reduce fluctuation, different methods are available to control the pitch angle of blades of windmill. In a previous work, we proposed the pitch angle control using minimum variance control, and output power leveling was achieved. However, it is a controlled output power for only rated wind speed region. This paper presents a control strategy based on average wind speed and standard deviation of wind speed and pitch angle control using a generalized predictive control in all operating regions for a WTG. The simulation results by using actual detailed model for wind power system show the effectiveness of the proposed method.     

Frequency deviation control by coordination control of FC and double-layer capacitor in an autonomous hybrid renewable energy power generation system

In this paper, a novel control strategy for frequency control in stand-alone application based on coordination control of fuel cells (FCs) and double-layer capacitor (DLC) bank in an autonomous hybrid renewable energy power generation system is implemented. The proposed renewable energy power generation subsystems include wind turbine generator (WTG), photovoltaic system (PV), FC system and DLC bank as energy storage system. The system performance under different condition has been verified by using real weather data. Simulation results demonstrate the validity of proposed studied hybrid power generation system feeding isolated loads in power frequency balance condition.     

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。     

基于混杂自动机的大型风力发电机组全程控制

风力发电系统是具有不确定性的复杂非线性系统,机组运行工况变化十分频繁。通过对风力发电机组的系统特性分析,发现风力发电系统呈现出混杂系统的典型特征。因此,基于混杂自动机理论建立了1.5 MW双馈型风电机组的混杂动态模型,并根据风力发电机组控制策略设计了能够在机组运行中实现全程自动化的混杂控制系统。仿真结果表明,基于混杂自动机的动态模型可以实现风电机组的全程模拟,所设计的混杂控制系统能够满足风电机组全程控制要求,证明了混杂系统理论应用于风力发电研究领域的有效性。     

Fractional‐order sliding mode control for hybrid drive wind power generation system with disturbances in the grid

The proposal of hybrid drive grid‐connected wind turbine based on speed regulating differential mechanism (SRDM) has been made in this paper to generate constant‐frequency power without fully‐ or partially‐rated frequency converters so as well improve electric power quality. However, disturbances in the power grid including sudden load fluctuation and sub‐synchronous resonance (SSR) can lead to the pulsating torque to act on the shaft section between SG and exciter at the main generator collector, such that the speed regulating accuracy of SRDM is seriously affected. As a result, this paper synthesizes a new‐type fractional‐order sliding mode controller (FOSMC) with a load torque observer (LTO) for the high‐accuracy speed control of permanent magnet synchronous motor (PMSM) in SRDM. Taking advantage of ridge regression algorithm, related parameters including rotational inertia and viscous friction coefficient of speed regulating system are calculated accurately. Finally, comparative experiments are carried out under four cases of mean of 5, 10, 13, and 21 m/s wind speeds to verify the satisfactory performances of designed FOSMC with LTO. Comparative experimental results show that FOSMC with LTO can effectively eliminate undesirable chattering effect. Additionally, under operating conditions of changing wind speeds, SSR, and sudden load fluctuation in power grid, the output speed of SRDM that corresponds directly to the frequency output of SG can be steadily and accurately regulated by using proposed control scheme. SRDM equipped with designed controller enables the power frequency to meet the National Standard of PR China perfectly.     

基于转矩极限的改进风电机组虚拟惯量控制策略

为解决大规模风电并网带来的系统频率稳定性降低问题,风电机组通过虚拟惯量控制可为系统提供短期频率支撑,然而惯性响应期间风电机组转速收敛缓慢,导致一部分转子动能被无故浪费;转速恢复阶段的有功突变易造成频率二次跌落。为此,提出基于转矩极限的改进风电机组虚拟惯量控制策略,实现在释放较少动能的前提下提供与传统策略相同的频率响应服务;并在频率步入准稳态时,借助时变功率函数开始转速恢复,实现转速快速恢复的同时缓解二次频率跌落。基于EMTP-RV仿真软件搭建包含风电场的电力系统模型,验证了所提策略的有效性。     

Dynamic contribution of variable-speed wind energy conversion system in system frequency regulation

Frequency regulation in a generation mix having large wind power penetration is a critical issue, as wind units isolate from the grid during disturbances with advanced power electronics controllers and reduce equivalent system inertia. Thus, it is important that wind turbines also contribute to system frequency control. This paper examines the dynamic contribution of doubly fed induction generator (DFIG)-based wind turbine in system frequency regulation. The modified inertial support scheme is proposed which helps the DFIG to provide the short term transient active power support to the grid during transients and arrests the fall in frequency. The frequency deviation is considered by the controller to provide the inertial control. An additional reference power output is used which helps the DFIG to release kinetic energy stored in rotating masses of the turbine. The optimal speed control parameters have been used for the DFIG to increases its participation in frequency control. The simulations carried out in a two-area interconnected power system demonstrate the contribution of the DFIG in load frequency control.     

Analysis of a fuel cell micro-grid with a small-scale wind turbine generator

If electric power is supplied using an independent micro-grid connected to renewable energy, it can flexibly match the energy demand characteristics of a local area. And an independent micro-grid is expected to be effective in cutting greenhouse gas discharge and energy costs, as well as in eliminating the need for an emergency power supply system. Since the output of renewable energy is unstable, other energy equipment needs to cover the stability of output. Thus, the operating conditions of an independent micro-grid that supplies power with natural power sources and fuel cells are investigated. The operation conditions of a fuel-cell independent micro-grid with wind power generation were investigated by numerical analysis. Step loads and an apartment house power load model were analyzed using the dynamic characteristics of a fuel cell obtained from experiments. The output of wind power generation and fuel cells is controlled by proportional-integral control of an independent micro-grid for rapid power demand change.     

Dynamics and stability of a hybrid wind-diesel power system

Dynamic system analysis is carried out on an isolated electric power system consisting of a wind turbine generator (WTG) and a diesel engine generator (DG). The 150 kW wind turbine generator is operated in parallel with the diesel generator to serve an average load of 350 kW. A comprehensive digital computer model of a hybrid wind-diesel power generation system, including the diesel and wind power dynamics for stability evaluation, is developed. The dynamic performance of the power system and its control logic are studied, using the time domain solution approach. A systematic method of choosing the gain parameter of the wind turbine generator pitch control by the second method of Lyapunov that guarantees stability is presented. The response of the power system with the optimal gain setting to the random load changes has been studied. Analysis of stability has further been explored using the eigenvalue sensitivity technique.     

Model‐based receding horizon control of wind farms for secondary frequency regulation

In this study, we propose the use of model‐based receding horizon control to enable a wind farm to provide secondary frequency regulation for a power grid. The controller is built by first proposing a time‐varying one‐dimensional wake model, which is validated against large eddy simulations of a wind farm at startup. This wake model is then used as a plant model for a closed‐loop receding horizon controller that uses wind speed measurements at each turbine as feedback. The control method is tested in large eddy simulations with actuator disk wind turbine models representing an 84‐turbine wind farm that aims to track sample frequency regulation reference signals spanning 40 min time intervals. This type of control generally requires wind turbines to reduce their power set points or curtail wind power output (derate the power output) by the same amount as the maximum upward variation in power level required by the reference signal. However, our control approach provides good tracking performance in the test system considered with only a 4% derate for a regulation signal with an 8% maximum upward variation. This performance improvement has the potential to reduce the opportunity cost associated with lost revenue in the bulk power market that is typically associated with providing frequency regulation services. Copyright © 2017 John Wiley & Sons, Ltd.     

Providing power reserve for secondary grid frequency regulation of offshore wind farms through yaw control

The ability to significantly contribute to the frequency regulation and provide valuable ancillary services to the transmission system operator (TSO) is one of the present wind farm (WF) challenges, due to the limitations of wind speed forecasting and insufficient power reserve in certain operating conditions notably. In this work, the feasibility of WFs to participate in frequency restoration reserve (FRR) through yaw control is assessed. To this end, a distributed yaw optimization method is developed to evaluate the power gain achieved by yaw redirection based on wind turbine cooperation and compared with a greedy approach. The method relies on a static wake model whose parameters are estimated in a systematic way from simulation data generated with FAST.Farm. Through a case study based on a scaled version of the Belgian Mermaid offshore WF, it is demonstrated that the requirements of the TSO are fulfilled both in terms of response time and level of power reserve for most wind directions. The assessment is limited to wind speeds below the rated speed of the considered wind turbines.     

稳定风电输出功率的控制策略研究

为稳定风电系统输出功率,提出一种在变流器的直流侧加入超级电容器(EDLC)储能的新拓扑结构,通过分析全功率双脉宽调制交-直-交变流器的控制策略,基于永磁直驱风电机组与电网连接的拓扑结构,提出超级电容器储能系统稳定风电系统输出功率的控制策略和输出功率的解耦控制方法,分析了风电系统输出功率初始值和超级电容器容量对输出功率稳定性的影响,并针对典型风速变化给出了输出功率初始值与超级电容器容量的整定范围。     

基于指数平滑与CEEMDAN的混合储能控制策略研究

随着风电并入电网渗透率的提高,其出力波动性会危及电力系统的安全稳定运行,混合储能装置的使用能很好地平抑风电并网的波动,改善电网的运行能力。为符合国家并网的标准,文章提出了混合储能控制策略。首先,运用指数平滑法滤除风电出力的高频分量得到并网功率;其次,采用自适应噪声的完整集合经验模态分解,将风电波动功率按频率高低依次划分为不同的固有模态分量,计算相邻固有模态分量的互信息来分离高频和低频分量,并分别由电池和超级电容承担低频、高频分量;为了消除荷电状态越限的问题,采用自适应调整分界点实现储能内部协调优化运行。算例结果表明,文章所提出的控制策略具有一定的适用性,能确保储能装置运行在安全荷电状态,延长其运行寿命。     

Nacelle anemometer measurement‐based extremum‐seeking wind turbine region‐2 control for improved convergence in fluctuating wind

For region‐2 operation of wind turbines in practice, the optimal torque gain can deviate from the nominal value because of the variations in turbine and wind conditions. The extremum‐seeking control (ESC) has shown its potential as a model‐free region‐2 control solution in some recent work; however, the ESC with rotor power feedback suffers from undesirable convergence under fluctuating wind. In this paper, we propose to use an estimated power coefficient as the objective function for the torque‐gain ESC, where the hub‐height free‐stream wind speed (FSWS) is estimated with the nacelle anemometer measurement on the basis of the so‐called nacelle transfer function (NTF) between the nacelle anemometer and met‐tower measurement. A sensitivity analysis is performed to quantify the impact of the wind speed estimation error on the estimation of power coefficient. An ESC integrated interregion switching scheme is proposed to avoid the load increase. Simulation results show that, compared with the power feedback‐based ESC, the proposed method can greatly improve the convergence rate of ESC under fluctuating wind, even under relatively large wind speed estimation error. Evaluation for the fatigue loads of wind turbine shows that the proposed control strategy induces mild increase of the wind turbine load.