含二级电压控制的风电场电压稳定性研究

为研究自动电压控制（Automatic Voltage Control,AVC）对电网电压质量和运行经济性的作用效果,采用了将双馈风电机组作为无功源的风电场自动电压控制设计方法,分析二级电压控制对风电场电压稳定性的影响.以IEEE14节点为例,采用基于遗传算法的协调二级电压控制模型,并通过基于MATLAB的电力系统软件包PSAT进行动态仿真验证.结果表明,二级电压控制可以大幅度改善风电场的电压-无功水平.     

A robust optimization approach to wind farm diversification

Wind farm diversification can smooth out the fluctuations in wind power generation and reduce the associated system balancing and reliability costs. Recent research has shown that wind farm diversification can be approached using mean–variance method. Traditional mean–variance wind farm diversification method is sensitive to the input data. To overcome the problem of lack of robustness, this paper proposes a novel wind farm diversification method based on robust optimization model. Under box and ellipsoidal uncertainty structures, the proposed robust optimization model can be formulated as a coupled problem composed of a linear programming problem and a conic quadratic programming problem. This model could be efficiently solved. Case studies are provided to demonstrate application of the model.     

Performance improvement in grid-connected fuel cell power plant: An LPV robust control approach

This paper presents a robust control scheme for power electronic interfaces of grid-tied fuel cell power plant. Firstly, a linear matrix inequality (LMI)-based PID controller is designed to control the duty cycle of the boost DC/DC converter, aiming to adjust the output DC voltage to an arbitrary reference value. Afterwards, linear parameter-varying (LPV) technique is utilized for robust control of grid-connected inverter to follow the desired real and reactive power demand of the grid, considering time-varying load and uncertain grid-impedance. Taking uncertainty of the system into account, all admissible variations are considered as a convex polytope. To guarantee a prescribed disturbance attenuation level and improve the transient response of the closed-loop system, H_∞ approach is exploited with pole placement consideration in terms of LMIs. Simulation results of the proposed controller compared to those of conventional PI controller, in presence of grid-voltage disturbance, validate high efficiency of the designed control.     

以并网点电压和机端电压平稳性为目标的风电场无功电压协调控制

现有的风电场无功电压控制方法均没有同时以风电场并网点和各机端电压为控制目标,因而不能完备地解决机端电压因扰动而发生偏移越界的问题。提出一种适用于变速恒频风电机组风电场的多目标无功电压控制方法。该方法通过调节风电机组及风电场内快速无功补偿装置优化风电场并网点及场内机组端电压,降低机组因电压越限而导致的脱网事故。以实际双馈风电机组的大型风电场为例,在RT-Lab实时仿真平台上验证了所提控制方法的有效性。     

风电场并网运行的无功补偿优化问题

风电场的功率输出具有很强的随机性,对风电场运行后的无功优化和系统稳定性问题进行了探讨。采用基于约束规划的无功补偿模型,提出基于随机模拟技术和Beta分布的粒子群优化解算方法。论述了Beta分布的粒子群算法的关键实施技术(Beta分布函数、初始可行解的产生策略、粒子的更新策略)及具体优化解算过程,并采用风电场并网运行的无功补偿优化及风电场并网运行的稳定性校验实例,表明该模型能满足可靠性和经济性条件下风电场所需的补偿容量,所采用的解算方法效果好。     

Analysis of voltage stability uncertainty using stochastic response surface method related to wind farm correlation

Wind speed follows the Weibull probability distribution and wind power can have a significant influence on power system voltage stability. In order to research the influence of wind plant correlation on power system voltage stability, in this paper, the stochastic response surface method (SRSM) is applied to voltage stability analysis to establish the polynomial relationship between the random input and the output response. The Kendall rank correlation coefficient is selected to measure the correlation between wind farms, and the joint probability distribution of wind farms is calculated by Copula function. A dynamic system that includes system node voltages is established. The composite matrix spectral radius of the dynamic system is used as the output of the SRSM, whereas the wind speed is used as the input based on wind farm correlation. The proposed method is compared with the traditional Monte Carlo (MC) method, and the effectiveness and accuracy of the proposed approach is verified using the IEEE 24-bus system and the EPRI 36-bus system. The simulation results also indicate that the consideration of wind farm correlation can more accurately reflect the system stability.     

基于VSC-HVDC的南汇风电场并网应用研究

风能作为一种绿色的可再生能源,将在取代传统一次能源、调整能源结构和环境保护中发挥重要的作用。在介绍柔性直流输电(VSC-HVDC)的原理和技术特点的基础上,将其与其他风电并网技术作了比较,详细说明了柔性直流输电技术在风电并网上的重大创新及巨大优势,并介绍了该技术在上海南汇风电场并网上的示范应用工程,表明了柔性直流输电技术在风电传输领域的广阔应用前景。     

经柔性直流输电并网的大型风电场频率控制策略

在大型风电场经柔性直流输电系统并入交流电网的场合,传统的电网调频方法难以适用。提出一种频率控制策略,分别在逆变侧换流器、整流侧换流器和风电机组上设计响应频率变化的控制环节。所有控制环节均基于本地测量的信号,无需远距离通信。该方法可以使风电场参与交流系统调频,此外,当系统故障引起柔性直流送出容量受限时,该方法可以自动降低风电机组功率,防止直流侧过压保护动作。     

Spatial dispersion of wind speeds and its influence on the forecasting error of wind power in a wind farm

Big wind farms must be integrated to power system.Wind power from big wind farms,with randomness,volatility and intermittent,will bring adverse impacts on the connected power system.High precision wind power forecasting is helpful to reduce above adverse impacts.There are two kinds of wind power forecasting.One is to forecast wind power only based on its time series data.The other is to forecast wind power based on wind speeds from weather forecast.For a big wind farm,due to its spatial scale and dynamics of wind,wind speeds at different wind turbines are obviously different,that is called wind speed spatial dispersion.Spatial dispersion of wind speeds and its influence on the wind power forecasting errors have been studied in this paper.An error evaluation framework has been established to account for the errors caused by wind speed spatial dispersion.A case study of several wind farms has demonstrated that even ifthe forecasting average wind speed is accurate,the error caused by wind speed spatial dispersion cannot be ignored for the wind power forecasting of a wind farm.     

含风电场的电力系统电压控制分区

提出了含风电场的电力系统电压控制分区的一种新的方法。将风电点出力离散为多个场景,并求取其期望场景。根据风机出力的特点修正了系统的无功电压灵敏度矩阵,然后根据电压幅值对于无功功率的灵敏度定义了电力系统各个节点的电气距离,再将其映射到一个多维空间中,依据此空间电气距离并应用免疫-中心点聚类算法将各节点进行归类。把问题转化为数学上的空间聚类问题。在新英格兰10机39节点进行仿真,其结果显示该方法能够合理地解决风机出力的随机性与系统分区要求尽量稳定的矛盾。     

Reactive power control of wind farm made up with doubly fed induction generators in distribution system

In recent years, the number of small size wind farm made up with doubly fed induction generators (DFIG) located within the distribution system is rapidly increasing. DFIG can be utilized as the continuous reactive power source to support system voltage control by taking advantage of their reactive power control capability. In this paper, considering both reactive power control and distribution network reconfiguration can be used to reduce power losses and improve voltage profile, a joint optimization algorithm of combining reactive power control of wind farm and network reconfiguration is proposed to obtain the optimal reactive power output of wind farm and network structure simultaneously. The proposed algorithm has been successfully implemented on the 16 bus distribution network and the results obtained demonstrate the efficiency of the algorithm.     

提升直流并网风电故障穿越能力的新方法

提出提升柔性直流并网的风电场系统故障穿越能力的新方法.分析了柔性直流输电的传统电流限幅器的不足,设计了动态改变限值的电流限幅器,该限幅器在电流扰动期间,能限制过电流,并能最大限度地提升输出功率.提出了新的转速储能方法,即利用风电机组自身的转子来实现提速储能,用以短时储存故障期间的过剩能量,以提高并网系统的故障穿越能力.仿真分析验证了所提方法的有效性.     

On power tracking and alleviation by a new controller for fulfilment of the damping and performance requisites for a variable speed wind system: An optimal approach

This paper addresses a new control strategy for a variable wind energy conversion system. The proposed controller aims to regulate the output power tightly in response to the desired value changes and alleviate power oscillations against the disturbances, including wind speed variation and fluctuation of the voltage magnitude, as voltage sag and swell. For the sake of straightforward analysis, an effective and reduced representation for the wind system is developed. In addition to the proper performance, the controller seeks to adequately fulfilment the damping requirements, as though both damping and performance requisites are taken into account control policy. Consequently, the proposed approach focuses on optimal tuning based upon a performance index incorporated into linear quadratic (LQ) cost function, which is subjected to the performance constraints. To validate the controller role, multiple simulation tests are carried out including set point tracking, disturbance rejection against wind speed, voltage sag and swell. Simulation results verify the proposed method features a satisfactory performance and sufficient damping, meeting both aspirations of the power regulation and disturbance suppression.     

风电场实现低电压穿越技术改造方案

我国风电设备制造业刚刚起步,风电机组普遍不具备低电压穿越(LVRT)能力,对风电机组进行改造所需的成本昂贵,因此考虑对风电场进行技术改造。分析并综述了国内外实现风电场LVRT技术改造的主要方案,现阶段并联动态无功补偿装置和串联动态电压调节器比较可行,未来储能装置由于其具备有功无功调节的多种功能,将会广泛地应用于风电场提高低电压穿越能力。     

Digital control and integration of a 192 MW wind farm with doubly fed induction generator into the Brazilian power system

This paper reports on design of digital control for wind turbines and its relation to the quality of power fed into the Brazilian grid on connecting to it a 192 MW wind farm equipped with doubly fed induction generators. PWM converters are deployed as vector controlled regulated current voltage sources for their rotors, for independent control of both active and reactive power of those generators. Both speed control and active power control strategies are analyzed, in the search for maximum efficiency of conversion of wind kinetic energy into electric power and enhanced quality of delivered power.     

Modeling and control of PMSG-based variable-speed wind turbine

This paper presents a control scheme of a variable-speed wind turbine with a permanent-magnetic synchronous generator (PMSG) and full-scale back-to-back voltage source converter. A comprehensive dynamical model of the PMSG wind turbine and its control scheme is presented. The control scheme comprises both the wind-turbine control itself and the power-converter control. In addition, since the PMSG wind turbine is able to support actively the grid due to its capability to control independently active and reactive power production to the imposed set-values with taking into account its operating state and limits, this paper presents the supervisory reactive power control scheme in order to regulate/contribute the voltage at a remote location. The ability of the control scheme is assessed and discussed by means of simulations, based on a candidate site of the offshore wind farm in Jeju, Korea.     

Output power leveling of wind turbine generators using pitch angle control for all operating regions in wind farm

Effective utilization of renewable energies such as wind energy instead of fossil fuels is desirable. Wind energy is not constant and windmill output is proportional to the cube of the wind speed, which causes the generated power of wind turbine generators (WTGs) to fluctuate. In order to reduce the output power fluctuation of wind farms, this paper presents an output power leveling control strategy for a wind farm based on both the average wind farm output power and the standard deviation of the wind farm output power, a cooperative control strategy for WTGs, and pitch angle control using a generalized predictive controller (GPC) in all WTG operating regions. Simulation results using an actual detailed model for wind farm systems show the effectiveness of the proposed method. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 158(4): 31– 41, 2007; Published online in Wiley InterScience ( www.interscience. wiley.com ). DOI 10.1002/eej.20448     

Reactive power control for improving voltage profiles: A comparison between two decentralized approaches

This paper is concerned with a local regulation of the voltage profiles at buses where wind power distributed generators are connected. In particular, the aim of the work is to compare two voltage control methods: the first based on a sensitivity analysis and the second on the designing of a fuzzy control system. The two methods are tested by means of simulations on a real distribution system and the results indicate that both methods allow the voltage profiles to be regulated at the wind generator connection bus within voltage standard limits, by taking into account the capability curves of the wind generators. Nevertheless, the fuzzy method presents more advantage in comparison with the sensitivity method. In fact, (i) it provides a gentler action control with a lower reactive power consumption during control operations as the reactive power profile follows better the voltage variations; (ii) the design of the fuzzy controller is independent from the knowledge of network parameters and its topology.     

An active power control strategy for a DFIG-based wind farm to depress the subsynchronous resonance of a power system

This study presents a novel auxiliary damping control strategy to depress subsynchronous resonance (SSR) oscillations in nearby turbine generators. In the proposed control strategy, SSR damping is achieved by adding turbine generator speed as a supplementary signal at the active power loop of the rotor-side converter (RSC) of doubly-fed induction generator (DFIG)-based wind farms. To design the SSR auxiliary damping controller, a transfer function between turbine generator speed and the output active power of the wind farms was introduced to derive the analytical expression of the damping coefficient. Then the damping effect of the active power of the DFIG-based wind farms was analyzed, and the phase range to obtain positive damping was determined. Next, the PID phase compensation parameters of the auxiliary damping controller were optimized by genetic algorithm to obtain the optimum damping in the entire subsynchronous frequency band. The last, the validity and effectiveness of the proposed auxiliary damping control were demonstrated on a modified version of the IEEE first benchmark model by time domain simulation analysis with the use of DigSILENT/PowerFactory.     

Direct-current vector control of three-phase grid-connected rectifier-inverter

The three-phase grid-connected converter is widely used in renewable and electric power system applications. Traditionally, control of the three-phase grid-connected converter is based on the standard decoupled d-q vector control mechanism. Nevertheless, the study of this paper shows that there is a limitation in the conventional standard vector control method. Some of the limitations have also been found recently by other researchers. To overcome the shortage of the conventional vector control technique, this paper proposes a new direct-current d-q vector control mechanism in a nested-loop control structure, based on which an optimal control strategy is developed in a nonlinear programming formulation. The behaviors of both the conventional and proposed control methods are compared and evaluated in simulation and laboratory hardware experiment environments, both of which demonstrates that the proposed approach is effective for grid-connected power converter control in a wide system conditions while the conventional standard vector control approach may behave improperly especially when the converter operates beyond its PWM saturation limit.