不同类型风电场对电网暂态稳定性的影响

研究了采用笼式和双馈式感应发电机的大规模风电场接入对电力系统暂态稳定性的影响。从理论上分析了笼式和双馈式感应电机的稳定机理;基于不同风电场和相关电网的数学模型,计算了电网发生故障后以故障临界切除时间表征的系统暂态稳定性;通过仿真计算,揭示了不同类型风电场对电网稳定性的影响,验证了理论分析结果。最后得出结论:笼式机组风电场的接入由于吸收无功而削弱了系统的稳定性;双馈式机组风电场接入对系统稳定性的影响,主要取决于接入点、电网结构、运行方式、故障类型等多种因素,其稳定性必须经具体的仿真计算才能确定。     

电网故障下风力发电系统的暂态电压控制策略

研究了由双馈感应式发电机和笼型异步发电机组成的风力发电系统的暂态电压控制策略。当电网发生故障时,单位功率因数运行方式下的双馈感应式发电机组和笼型异步发电机组都不能够提供无功功率以帮助系统恢复稳定运行。本文提出了一种基于PI控制器的暂态电压控制策略并对其进行仿真分析。仿真结果表明,故障清除后能够提高双馈感应式发电机和笼型异步发电机的暂态电压稳定性,同时改善了系统稳定运行的能力。     

电网电压骤降故障下双馈风力发电机建模与控制

双馈感应发电机（DFIG）在变速恒频风力发电中得到广泛应用,对DFIG采用矢量控制可使风电系统实现最大风能追踪和有功、无功解耦调节,从而获得优良的发电运行性能。但在传统的矢量控制方式中,通常认为是无穷大理想电网,忽略了定子励磁电流变化的动态过程,从而得到简化的DFIG数学模型,并以此作为电流内环控制器的设计依据。这种控制器在电网正常的情况下可使系统获得优良的动静态特性,但当电网出现故障时,其控制性能将恶化。为了提高电网电压故障情况下DFIG不间断运行能力,文中以DFIG的精确数学模型为依据,针对传统的2种矢量控制方式的不足,提出了改进的控制方案,并对改进前后电网电压骤降情况下DFIG的动态过程进行了仿真对比,结果表明改进方案可以有效控制转子电流,保护转子励磁变频器,提高DFIG变速恒频风电系统在电网故障下的不间断运行能力,是并网DFIG风力发电机的一种有效、实用的控制策略。     

电网故障下并网异步风电机组的暂态特性分析

研究了由笼型和双馈型异步风电机组组成的风电场并网后风电机组的暂态行为,并对比分析了在同一接入点接入不同比例容量的笼型异步发电机和双馈异步发电机时,外部三相短路故障对风力发电机组电压和转速的影响。提出了在双馈型风电机组中采用一种PI控制器,以提高风电场的稳定运行能力的方案。仿真结果表明,故障清除后,能有效地提高风电机组的稳定运行能力。该试验结果可为风电场的建设提供参考。     

永磁直驱风电机组故障穿越优化控制策略研究

永磁同步发电机构成的直驱型变速恒频风力发电系统通过全功率变流器与电网连接,当电网发生严重故障时,不仅对HVDC设备造成损害,甚至可能影响风力发电系统的整体安全稳定运行。对系统故障期间直流电压失稳的机理进行了分析,基于永磁同步发电机转子的惯性储能特性以及网侧换流器的无功补偿能力,提出一种适用于提高永磁直驱风电机组故障穿越能力的优化控制策略。在网侧故障期间通过分段式转速控制调整风机侧输入的有功并对网侧无功进行补偿,减小了中间直流系统注入的不平衡功率,抑制了故障期间直流电压的骤升。应用PSCAD/EMTDC电磁暂态仿真软件建立单机系统模型,仿真结果验证了所提出的控制策略的有效性。     

风电多端柔性直流并网系统交流送出线故障短路电流解析

随着海上风电的发展和区域风电装机容量的增大,规模化新能源电源通过多端柔性直流(MMC-MTDC)并网成为风电并网的一种趋势.然而,考虑MMC-MTDC和永磁风机构成的多换流器系统协调故障穿越及其故障特征解析尚未得到有效解决,亟待针对性研究.文中首先对传统风电MMC-MTDC并网系统故障穿越策略进行优化,给出了可行的穿越...     

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.     

制动电阻对变速双馈风电机组故障穿越能力的影响研究

为保持系统稳定,必须要求风电机组具有故障穿越能力.双馈风电机组故障穿越能力已成为研究热点.介绍了故障穿越标准,分析了双馈风电机组暂态特性与制动电阻的工作原理,详细分析电网电压跌落情况下,制动电阻接在风电场升压变压器低压侧与接在风电机组机端对双馈风机故障穿越能力影响.试验结果表明:故障期间投入制动电阻,能有效提升双馈风电场故障穿越能力.     

基于磁链追踪的双馈风力发电系统低电压穿越控制

根据当今世界对风能转换系统提出的必须具有低电压穿越能力的要求,研究了电网跌落对双馈风力发电机的影响。在电网跌落时双馈风力发电机运行特点的基础上,分析并提出了一种基于磁链追踪的双馈风力发电系统低电压穿越控制策略,有效地抑制了双馈风力发电机定、转子过电流,保证了变流器的安全运行,实现了双馈风力发电机在电网跌落时的低电压穿越。依据理论分析,建立了双馈风力发电机磁链追踪控制模型,并通过MATLAB/SIMULINK平台进行仿真研究,仿真结果证实了所提控制策略的可行性和有效性。     

Smoothing of Wind Power Fluctuations for Permanent Magnet Synchronous Generator-Based Wind Energy Conversion System and Fault Ride-through Consideration

Due to the increment of penetration level of wind power generation, output power fluctuation is one of the most important issue's that can destabilize the power system operation. This article mainly deals with the smoothing of the output power fluctuations of a wind energy conversion system based permanent magnet synchronous generator and fault ride-through enhancement during a grid fault. The concerned wind energy conversion system based permanent magnet synchronous generator adopts an AC-DC-AC converter system. The proposed control method limits the wind energy conversion system output power by adjusting the pitch angle of the wind turbine blades when wind speed is above the rated wind speed. In the grid-side converter, a fuzzy logic controller is used to determine the torque reference for which the kinetic energy stored by the inertia of wind turbine can smooth the output power fluctuations of the permanent magnet synchronous generator. Also, the DC-link voltage, controlled by the grid-side inverter, is adjusted in accordance with the output power fluctuations of the permanent magnet synchronous generator using a voltage smoothing index. Moreover, in this aticle, the proposed method ensures that the wind turbine stays operational during grid faults and provides fast restoration once the fault is cleared. To show the effectiveness of the proposed method, simulations under different conditions have been performed by using MATLAB/Simulink® (The Math Works, Natick, MA, USA).     

Pitch control based on voltage dip detection for improving the LVRT of wind farm

For the stability of power systems including large‐scale generation of wind power, wind farms are expected to fulfill the requirement with the capability to remain connected to the systems during a momentary voltage dip occurring in power networks. This has prompted many utilities to adopt the low‐voltage ride‐through (LVRT) of wind turbine generators (WTGs) as one of the requirements in interconnection of large wind farms. This paper presents a new method of pitch angle control for fixed‐speed wind turbine (FSWT) to achieve LVRT capability improvement. The FSWT is equipped with directly grid‐coupled squirrel‐cage induction generator and the LVRT behavior of such wind turbine is closely related to the overspeeding of wind turbine rotor during voltage dip. If the turbine rotor speed can be reduced quickly during voltage dip so as not to rise over the maximum speed, then the sudden disconnection of WTG can be avoided. The proposed pitch control system can modify the pitch angle in the short response time by the coordination of protective relay. Then the pitch angle is adjusted by a feedback proportional integral controller based on the measurement of induction generator terminal voltage. Simulation study shows that the application of the proposed pitch control system can improve the LVRT performance of a wind farm equipped with FSWTs. © 2011 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

几种变速恒频风力发电系统控制方案的对比分析

阐明了为最大限度利用风能,风力发电系统应采用变速恒频控制策略,并分析了变速恒频风力发电系统中功率转换子系统的主要组成环节。对4种分别采用笼型异步发电机、交流励磁双馈发电机、无刷双馈发电机和永磁发电机的变速恒频风力发电系统进行了性能对比分析。     

IGBT型Crowbar保护电路仿真研究

采用Crowbar保护电路可以极大地提高双馈式风电系统的低电压穿越能力(LVRT)。建立了双馈风力发电机(DFIG)的数学模型,对IGBT型Crowbar保护电路关键参数—卸能电阻最优值范围进行研究。并通过MATLAB/Simulink搭建了变速恒频DFIG风力发电系统模型,仿真表明当电网电压大幅度跌落时采取Crowbar保护电路的必要性。     

Modeling of Five-Phase,Self-Excited Induction Generator for Wind Mill Application

Wind turbines with higher power ratings are desired to reduce construction cost and maintenance time and increase energy yields. Three-phase induction generators are widely used in renewable power generation. Self-excited, squirrel cage induction generators are ideally suited for remote, standalone applications of low and medium power generation. The emerging multiphase induction generator (MPIG) with phases more than three is receiving significant attention for high power applications. This paper aspires at the performance investigation of five-phase induction generator (FPIG) in self-excited mode for standalone wind applications. The dynamic model of FPIG is developed using Matlab/Simulink. The performance of wind-driven FPIG under different operating conditions has been analyzed. The process of voltage build-up, current and torque under no load and loaded conditions are presented. The results are compared with three-phase self-excited induction generator (SEIG) to show the effectiveness of FPIG for high-power wind generation.     

A novel method to improve low‐voltage ride‐through capability of wind turbine generators

With increasing penetration of wind farms, power grids have responded by developing specific grid codes to maintain their stability. One of the main grid codes is the low‐voltage ride‐through (LVRT) capability, which requires the wind generator to remain connected when the grid voltage sags for a certain time period. A wind farm with squirrel cage induction generators suffers this LVRT problem the most because of their direct connection to the grid and reactive power consumption. In this paper, a new method is proposed to solve this problem by shunt‐connecting a motor‐driven mechanical load to the cage wind generator. For driving mechanical loads, the induction motor is most widely used in industries. This paper studies the terminal voltage holding effect of an induction machine during grid voltage sag due to the magnetic flux holding effect and the saturation characteristic. Taking advantage of this effect, the induction motor that is used for driving mechanical load is then proposed to improve the LVRT capability of wind turbine generators. Furthermore, the change of the rotating speed or slip of the induction machine is found to have a great impact on improving the LVRT. By adding some inertia to the motor‐driven mechanical load, an enhanced voltage holding effect, and therefore LVRT improvement, is expected for the wind farm. Both simulation and experimental results prove the effectiveness of the proposed method. © 2013 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

基于双单片机的变速风力发电系统的研究

描述了一个追踪能量输出最大化的变速恒频风力发电系统，该系统由一鼠笼感应发电机和一交直交变磐系垫相连而组成，在此系统中使用了两个80C196MC电机专用单片机分别去实现输出能量最大化和单位功率因数电能同步上网。     

Low and high voltage ride-through of DFIG wind turbines using hybrid current controlled converters

Doubly fed induction generators have been recognized as the dominant technology used in wind generation systems. However, this type of wind generator is very sensitive to the drop/rise in the supply voltage and without efficient “ride-through” strategy, continuous operation of DFIG may fail due to destructive overcurrents in the rotor winding or large overvoltages in the dc-link capacitor. This paper introduces a hybrid current control scheme, implemented in the rotor-side and grid-side converters of DFIG, to enhance low and high voltage ride-through capacities of DFIG-based wind turbines. The proposed control scheme is constituted of two switching strategies integrated with a supervisory control unit: standard PI current controllers for normal operating conditions and vector-based hysteresis current controllers for DFIG protection during severe voltage sag/swell conditions. Time-domain simulation studies are carried out to examine the effectiveness of the proposed ride-through strategy under various types of grid disturbances. It is shown that the proposed controller constrains the rotor current and dc-link voltage within the safety limits of DFIG and as a result, the wind generator can comply with the strict low/high voltage ride-through requirements stipulated by modern grid codes.     

基于储能和无功优化的直驱机组海上风电场低电压穿越策略

针对直驱永磁机组海上风电场中的低电压穿越问题,提出了一种基于储能和无功优化控制的低电压穿越控制方案。采用锂电池作为分散式储能设备,吸收故障时刻直流母线上多余功率;同时以网侧变流器输出有功功率、直流母线电压、机端电压作为评价指标,对风电场中各台风电机组低电压穿越能力进行评估,优化控制各台机组的无功出力,从而有效抑制电网故障时机组直流侧电压上升,同时支撑并网点电压恢复。以某海上风电场为例进行仿真分析,仿真结果表明了该方案能显著提高风电场低电压穿越能力。     

永磁风电系统低电压穿越控制策略研究

针对Boost升压型永磁直驱型风电系统,分析了其发电机侧和网侧变流器的控制策略.为增强其低电压穿越能力,提出了一种基于转子储能和网侧无功优先输出的控制策略.通过减小发电机的有功输出来降低直流侧过电压,通过控制网侧无功输出来提升电网电压.基于Matlab/Simulink 7.10搭建了仿真模型.仿真结果证明了该控制策略的有效性.     

Power Control of Directly Driven Wind Generation System Based on Superconducting Magnetic Energy Storage

The increasing wind power penetration poses significant technical problems to the development of electric power systems. In this article, an integrated control strategy is proposed based on the characteristics of the directly driven permanent magnet synchronous generator wind turbine. The directly driven permanent magnet synchronous generator wind turbine is incorporated with superconducting magnetic energy storage, which can smooth the wind power fluctuations, enhance the low-voltage ride-through capability of the wind generation system, and achieve an uninterruptible power supply to local loads under isolated grid operation. According to the MATLAB/SIMULINK-based (The MathWorks, Natick, Massachusetts, USA) digital computer simulation model, the proposed control strategy is confirmed to be effective in power control of grid operation.