含STATCOM的双馈电机风电场无功电压协调控制策略

为增强风电场并网点电压稳定性,提出了变速恒频双馈风电场与动态无功补偿装置STATCOM间的无功电压协调控制策略。电网故障导致风电并网点不同深度的电压跌落时,根据双馈风机Crowbar保护投切状态,对DFIG风电机组转子侧及网侧变流器与STATCOM进行无功功率分配,协调控制促进风电场LVRT期间风电并网点电压的快速恢复。最后,在DIg SILENT/Power Factory仿真软件中建立了风电场和STATCOM控制模型,通过仿真验证该控制策略的有效性。     

基于Crowbar的双馈风电系统低电压故障下无功控制

在电网电压发生跌落故障期间,基于Crowbar电路的双馈风力发电系统需要吸收大量无功功率。通过分析故障下DFIG系统的运行特点,建立了变桨距角控制模型及网侧变流器的STATCOM控制模型,Crowbar电路动作后,利用变桨距系统调节桨距角来抑制系统转差率,减小系统从电网中吸收无功功率,同时将网侧变换器切换成STATCOM工作模式,为系统提供无功功率补偿,在PSCAD/EMTDC平台进行暂态仿真研究。结果表明,在故障期间Crowbar电路启动后,通过该控制策略能避免系统从电网中吸收过量无功功率,有助于主电网电压的重建和恢复,验证了所提方法的有效性和正确性。     

电网故障时双馈风电机组定子电压特性及影响分析

随着以双馈风力发电机为主的风力发电的大规模并网,电网故障期间并网双馈风电机组对电网的影响不断显现,使电网安全稳定运行面临着严峻挑战。为了有效评估双馈风电机组的暂态过程及其对电网的影响,需要掌握电网故障期间双馈发电机机端电压的大小及变化规律。基于双馈发电机的暂态过程,推导了稳态运行以及外部电网三相短路下双馈发电机定子电压的表达式。在此基础上,对双馈发电机定子电压的暂态特性进行了研究,明确了定子电压的影响因素,分析了电网故障时双馈风电机组对电网暂态电压分布的影响。最后通过仿真进一步分析了定子电压的变化规律并验证了推导的正确性。     

储能型双馈风电场联合STATCOM的无功协调控制

针对传统双馈风电机组(DFIG)低电压穿越(LVRT)能力不足问题,提出了储能型双馈风电场联合STATCOM的无功协调控制。该控制是在网侧变流器（GSC）原有的模型上将超级电容经隔离型DC/DC变换器并联到风机直流侧,以此吸收故障期间直流侧产生的不平衡功率;在发生低电压故障时,根据超级电容投入情况,对两侧变流器和并联在风机出口母线上的STATCOM进行无功协调控制来支撑电网电压;同时超级电容储能装置采用电压电流双闭环控制,满足了系统稳定性和经济性的要求。仿真结果表明：该方法应用在风电并网系统中可以使DFIG的LVRT能力得到极大的提升。     

基于超级电容器储能的STATCOM对直驱风力机并网性能改善的研究

本文主要研究了采用基于超级电容器的静态同步补偿器(STATCOM)的永磁(PMSG)直驱变速风力机控制策略。基于Matlab/Simpower实现对风力发电机侧整流器最大功率提取、电网侧逆变器和STATCOM的控制策略,采用不同容量超级电容器储能的STATCOM系统在电网出现故障或者受到干扰时提升风力发电系统稳定状态和动态性能。大量仿真结果表明:与传统的STATCOM相比,采用基于超级电容器的STATCOM能有效改善并网过程中出现的电压闪变及波动,减小频率的波动,并能对故障期间的电流进行有效控制,从而较为显著地改善了直驱风力发电系统的有功、无功功率,提升了风电并网系统故障穿越能力和动态性能。     

弱电网情况下双馈风电机组改进虚拟感抗控制方法

当前弱电网条件下双馈风电机组的运行稳定性问题受到广泛关注。在同步旋转坐标系下建立了综合考虑锁相环、转子侧电流环和功率环控制器影响的双馈风电机组等效输入导纳模型。在此基础上,结合广义奈奎斯特稳定判据分析了增大转子侧电感对系统稳定性的提升作用,由此提出在控制器中引入虚拟感抗提高系统稳定性的方法。相对于传统的直接在转子侧电流环中引入虚拟感抗,在设计基于虚拟感抗的控制器时,充分考虑锁相环耦合弱电网扰动对双馈风电机组运行稳定性带来的不利影响,提出了改进的控制方法。通过广义奈奎斯特判据证明了该方法能有效提高弱电网条件下双馈风电机组的运行稳定性。在MATLAB/Simulink中搭建了1.5 MW的双馈风电机组详细模型,通过仿真验证了所提改进控制器对提高系统稳定性的有效性。     

电网对称故障时双馈感应发电机不脱网运行的系统仿真研究

利用经实验验证的时域仿真模型对一典型的2MW双馈感应风力发电系统在电网对称故障时的控制和响应进行仿真研究。与在电网故障时将转子端部直接短接的保护方案相比较,采用所提出的电网故障励磁控制与正常运行时的风能跟踪控制相结合,可以保证发电机迅速恢复有功输出,从而提高整个电力系统在故障切除后的运行稳定性。针对电网对称故障时发电机不脱网运行的可控范围进行仿真计算的结果表明:典型双馈感应风力发电机可在电网故障引起发电机变压器系统侧电压最低下降到30％额定电压时仍可保持不脱网运行。对影响电网故障励磁控制性能的各种因素,包括发电机故障前初始运行点及电机参数进行了研究,发现适当增加发电机漏感或定予侧电阻有助于进一步提高电网故障时励磁控制的效果。     

双馈风电机组低电压穿越特性的试验研究

低电压穿越能力正逐渐成为大型并网风电机组的必备功能之一,要求风电机组在电网电压跌落发生时保持并网,故障消除后快速恢复正常运行。在分析双馈机组电压跌落特性的基础上,采用了转子主动式Crowbar电路和直流侧卸荷电路相结合的方法来实现双馈风电机组的低电压穿越功能,讨论了具体的低电压穿越控制策略,通过仿真验证了电路结构和控制策略的正确性。在实验室10 kW双馈机组实验平台上,采用电压跌落发生器模拟电网电压跌落故障,进行了电网电压跌落至额定电压20%时不同持续时间的测试,证实了所采用的低电压穿越控制策略的有效性。     

VSCF-DFIG在电压瞬间跌落情况下的应对策略

变速恒频（VSCF）双馈感应发电机（DFIG）在电网电压跌落的情况下,通过连接在转子绕组上的电阻来为电压跌落期间在转子侧产生的浪涌电流提供一条通路,从而达到限制转子回路最大电流的目的。在电网需要时,快速向电网提供无功功率,调节电网电压和稳定弱电网。通过保持系统稳定性,减少电压崩溃的危险,降低电网解列的影响。所有结果通过了仿真验证。     

静止同步补偿器增强风电场的低电压穿越能力的应用分析

提出利用静止同步补偿器(static synchronous compensator,STATCOM)快速补偿无功功率以增强双馈式风电机组和直驱式风电机组的低电压穿越能力.首先阐述了风电机组的动态模型,然后给出了STATCOM控制模型,最后将STATCOM装置应用到合风电场的电力系统中,比较加装STATCOM前后母线56和母线12的电压以及风电机组输出功率的变化情况.仿真结果表明,STATCOM能有效地帮助风电机组在电网发生故障后恢复机端电压和故障点电压,并防止风电机组输出功率振荡,使风电场在故障发生后能保持连续运行,增强了风电机组的低电压穿越能力.     

A novel controllable crowbar based onfault type protection technique for DFIGwind energy conversion system usingadaptive neuro-fuzzy inference system

This paper proposes a novel controllable crowbar based on fault type (CBFT) protection technique for doubly fed induction generator (DFIG) wind energy conversion system connected to grid. The studied system consists of six DFIG wind turbines with a capacity of 1.5 MW for each of them. The operation mechanism of proposed technique is used to connect a set of crowbar resistors in different connection ways via activation of controllable circuit breakers (CBs) depending on the detected fault type. For each phase of DFIG, a crowbar resistor is connected in parallel with a controllable CB and all of them are connected in series to grid terminals. The adaptive neuro-fuzzy inference system (ANFIS) networks are designed to detect the fault occurrence, classify the fault type, activate the CBs for crowbar resistors associated with faulted phases during fault period, and deactivate them after fault clearance. The effectiveness of proposed CBFT protection technique is investigated for different fault types such as symmetrical and unsymmetrical faults taking into account the single-phase to ground fault is the most frequently fault type that occurs in power systems. Also, a comparison between the behaviours of studied system in cases of using traditional parallel rotor crowbar, classical outer crowbar, and proposed CBFT protection techniques is studied. The fluctuations of DC-link voltage, active power, and reactive power for studied system equipped with different protection techniques are investigated. Moreover, the impacts of different crowbar resistance values on the accuracy of proposed technique are studied. The simulation results show that, the proposed technique enhances the stability of studied wind turbine generators and contributes in protection of their components during faults.     

Low voltage ride-through enhancement of DFIG-based wind turbine using DC link switchable resistive type fault current limiter

Doubly-fed induction generator (DFIG)-based wind turbines utilise small-scale voltage sourced converters with a limited overcurrent withstand capability, which makes the DFIG-based wind turbines very vulnerable to grid faults. Often, modern DFIG systems employ a crowbar protection at the rotor circuit to protect the rotor side converter (RSC) during grid faults. This method converts the DFIG to a squirrel cage induction generator, which does not comply with the new grid codes. The recent grid codes need wind turbines to stay connected to the utility grid during and after power system faults, especially in high penetration level of wind power. Furthermore, the crowbar switch is expensive. This paper proposes a novel DC-link switchable resistive-type fault current limiter (SRFCL) to improve the LVRT capability of the DFIG. The proposed SRFCL is employed in the DC side of the RSC. The SRFCL solves crowbar protection activation problems and eliminates subsequent complications in the DFIG system. The proposed SRFCL does not have any significant impact on the overall performance of the DFIG during normal operation. Whenever the fault, whether symmetrical or asymmetrical, occurs, the SRFCL not only limits rotor over-currents but also prevents rotor speed acceleration and restricts high torque oscillations even during zero grid voltage, as recommended by some grid codes. To prove the effective operation of the SRFCL on the RSC fault current limitation, analytical analysis is performed in each switching interval. The proposed approach is compared with the crowbar-based protection method. Simulation studies are carried out in PSCAD/EMTDC software. In addition, a prototype is provided to demonstrate the main concept of the proposed approach.     

双馈变速风电机组低电压穿越控制

当系统中风电装机容量比例较大时,系统故障导致电压跌落后,风电场切除会严重影响系统运行的稳定性,这就要求风电机组具有低电压穿越（Low Voltage Ride Through,LVRT)能力,保证系统发生故障后风电机组不间断并网运行。分析了双馈风电机组LVRT原理和基于转子撬棒保护(crow-bar protection)的LVRT控制策略,在电力系统仿真分析软件DIgSILENT/Power Factory中建立了双馈风电机组模型及其LVRT控制模型,以某地区风电系统为例进行仿真计算,分析转子撬棒投入与     

考虑抑制DFIG机群脱网的风电场无功补偿配置新方法

随着大规模风电并网,电网故障情况下风电机群连锁脱网事故严重威胁电网安全稳定运行。为此,从抑制DFIG机群脱网的角度,提出了一种考虑抑制双馈异步风力发电机（doubly-fed induction generator,DFIG）机群脱网的风电场无功补偿配置新方法。该方法首先以风电场为中心进行无功平衡初步分析,通过无功需求和有功传输之间的定量关系,确定风电场所需要配置的低压电抗器组和低压电容器组容量。然后通过不同负荷方式下风电出力波动和线路N-1运行时的风电场母线电压无功分析,校核初步配置方案对系统静态安全的适应能力。最后,在分析电网故障情况下DFIG机群无功需求特征基础上,通过加入一定容量的静止同步补偿器（static synchronous compensator,STATCOM）来抑制机群脱网,从而使无功补偿方案能满足系统安全运行的要求。该方法已应用到了某省网大容量风电接入220 kV的无功配置专题研究中,在经济和技术上是可行的和有效的。     

Review of DFIG wind turbine impact on power system dynamic performances

Recently, the variable‐speed wind turbine with doubly fed induction generator (DFIG ) has drawn significant attention because of its many advantages such as small power converter rating, the ability to control the output power, etc. Nevertheless, the large penetration of DFIG wind turbines may affect the power system dynamics. This paper provides a general review of the DFIG wind turbine's impact on power system dynamic performances such as frequency stability, transient stability, small‐signal stability, and voltage stability. Besides, ancillary services from the DFIG wind turbine for the power grid, such as frequency support, reactive power, and voltage support, are explained. Especially, the survey emphasizes power oscillation damping methods by the DFIG wind turbine. © 2017 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

变速恒频双馈异步风力发电系统低电压穿越技术综述

随着以变速恒频(VSCF)双馈异步发电机(DFIG)为主体的大型风力发电机组在电网中所占比例的快速提高,电力系统对并网风力发电机在外部电网故障、特别是电网电压骤降故障下的不问断运行能力提出了更高的要求.本文首先分析了电网电压骤降对DFIG运行的影响,提出了DFIG风力发电系统低电压穿越运行的控制目标,继而总结、评价了各种适合于DFIG风力发电系统的低电压穿越技术,最后指出了DFIG风电系统低电压穿越技术的优化方向,以期展示该技术的最新进展及发展趋势.     

双馈感应风力发电系统低电压穿越控制策略研究及其分析

基于双馈感应发电机(DFIG)风力发电系统模型,通过分析电网电压跌落情况下的各种运行状况,提出在电网严重故障期间,采用Active Crowbar电路和直流侧卸荷电路保护变流器和避免直流侧电压过压。在电网故障恢复期间,Crowbar电路的再次投入使得系统无功需求增大。并在网侧变流器的功率容量范围内,提出一种网侧变流器无功功率的控制策略来实现对电网无功支持,以助于电网故障恢复以及加快机端电压恢复。基于PSCAD/EMTDC平台建立了仿真系统模型并验证了该控制策略的有效性。该控制策略满足了风电机组并网的低电压穿越,有效提高了DFIG风电机组运行的可靠性。     

Operation and control of a grid-connected DFIG-based wind turbine with series grid-side converter during network unbalance

This paper proposes a control scheme of a grid-connected doubly-fed induction generator (DFIG) wind turbine with series grid-side converter (SGSC) to improve the control and operation performance of DFIG system during network unbalance. The behaviors of DFIG system with SGSC under unbalanced grid voltage conditions are described. The SGSC is controlled to inject voltage in series to balance the stator voltage. Therefore, the adverse effects of voltage unbalance upon the DFIG such as large stator and rotor current unbalances, electromagnetic torque and power pulsations are removed and the conventional vector control strategy for the rotor-side converter (RSC) remains in full force under unbalanced conditions. Meanwhile, three selective control targets for the parallel grid-side converter (PGSC), such as eliminating the oscillations in total active or reactive power, or no negative-sequence current injected to the grid are identified and compared. Besides, the proportional resonant controllers in the stationary reference frame are designed for both the SGSC and PGSC to further improve the dynamic performance of the whole system. Finally, the ratings and losses of the SGSC and the injected transformer are discussed and the effectiveness of the proposed control scheme is verified by the simulation results of a 2 MW DFIG-based wind turbine with SGSC under steady state and small transient grid voltage unbalance.     

STATCOM在风力发电场中的应用

在同步旋转坐标系下采用STATCOM(static synchronous compensator)和异步发电机风力发电系统的暂态数学模型,采用基于非线性反馈线性化的逆系统方法,构造出STATCOM的伪线性系统,然后采用滑模变结构控制理论设计出STATCOM的滑模变结构控制器。然后,以随机风和电网大扰动为例,采用STATCOM对并网风电场的电能质量和稳定性问题进行仿真。结果表明:采用该控制策略的STATCOM可很好地改善风电场的电能质量和稳定性。     

ANN-Based STATCOM Tuning for Performance Enhancement of Combined Wind Farms

Although the wind farms based on squirrel cage induction generators (SCIG) is cheaper than the wind farms based on doubly fed induction generators (DFIG), it is always in desperate need for reactive power compensation. Nevertheless, the wind farms based on DFIG are expensive compared with the SCIG wind farm, it features by its ability to control the active power independent of reactive power. However, combined wind farm (CWF) has been developed to collect the benefits of SCIG and DFIG wind turbines in the same wind farm. In this article, artificial neural network (ANN) is used to evaluate gain parameters of static synchronous compensator (STATCOM) in order to improve the stability performance of CWF. The impact of tuned STATCOM on the performance of CWF during gust wind speed and during three-phase fault is comprehensively investigated. The performance of CWF with STATCOM tuned by ANN is compared with its performance when the STATCOM tuned by the multiobjective genetic algorithm (MOGA) and whale optimization algorithm (WOA). The results show that the performance of CWF can be enhanced using STATCOM tuned by ANN more than MOGA and WOA.