风电氢联产系统功率平滑控制仿真研究

风能的随机性会引起风力发电出力不平稳,与此同时,电网电压跌落会给风电机组带来脱网运行的风险。针对该问题,文章将电解槽-储氢罐-质子交换膜燃料电池循环系统作为储能装置,接入风力发电系统背靠背变换器直流侧,构成了风电氢联产系统。在风电过剩时,系统通过电解水制氢储存多余电能;在风能不足时,消耗氢气产生电能,补偿不足的有功功率。文章在分析系统构成及运行方式的基础上,设计了各组成单元协调控制策略。MATLAB仿真结果表明:在文章提出的控制策略作用下,系统可以有效地抑制风速随机变化引起的输出功率的波动;配电网电压跌落时,系统具有较强的抵御风机脱网的能力。     

基于转子储能的全功率变速水电机组低电压穿越控制策略研究

全功率变速水力发电机组是水力发电机组变速运行主要方式之一,能更快速度响应电网功率变化需求,对间歇性与随机性强的新能源消纳具有重要意义,其机组的低电压穿越能力是保障机组稳定并网运行的关键。提出了一种基于机组转子储能的低电压穿越控制策略,充分利用水力发电机组转子储能能力强和机组输入功率可以调节的特点,采用转子储能和调速器调节吸收控制电网电压跌落期间的机组不平衡能量,并根据电网电压跌落幅值通过网侧变流器向电网提供无功电流支撑。建立了系统各部件的数学模型,通过仿真比对了提出的控制策略与传统的策略,仿真结果表明提出的控制策略能有效抑制直流母线过电压,并向电网提供无功电流支撑,提高了全功率变速水力发电机组的低电压穿越能力。     

大型光伏电站变结构低电压穿越控制策略研究

通过分析大型光伏电站在电网故障下的特征,研究了大型光伏电站低电压穿越的变结构控制策略。在电网发生故障时,通过变结构控制策略,限制逆变器交流侧电流幅值,同时切换网侧电压外环控制,通过比例调节器,将电压跌落深度转换为无功电流缺额,向电网发送无功功率,提高电网电压的恢复能力,并将此控制策略应用于多台并网逆变器联合运行。仿真结果表明,所提出的变结构控制策略能够有效限制交流侧电流幅值,使逆变器不脱网运行,提高了故障点电压的恢复能力,实现光伏电站低电压穿越的要求     

直驱式风电系统网侧变换器控制策略研究

研究了一种适合于直驱式风电系统网侧变换器的控制策略,该变换器选用三相电压源型PWM六桥臂拓扑结构。建立了网侧PWM变换器的数学模型,基于电网电压矢量定向,提出采用d,q轴电流线性化解耦控制策略及空间电压矢量SVPWM调制方式。在Matlab环境下的仿真结果表明,该系统运行稳定,动态响应快,输出直流电压稳定,且脉动很小,各项性能优良。     

双馈风电系统高电压穿越的节能控制策略

在研究双馈风力发电系统高电压穿越的节能控制问题的过程中,考虑到外部风力环境变化较大,需保持变换器的稳定性节能控制。传统节能控制方法不仅动态及稳态性能差,而且节能控制策略相对复杂。为了提高节能控制效果,提出采用串联网侧变换器的双馈风电系统高电压穿越的节能控制策略,向串联网侧变换器的控制向电机定子侧和电网间添加合理的控制电压,按照电网电压定向的同步旋转,给出d-q轴系下SGSC的电压控制方程,保持DFIG定子端电压不变,过滤DFIG定子磁链中的暂态直流分量。当双馈风电系统电压及电流均不超限时,对转子侧变换器和并联网侧变换器的输出电压矢量进行节能控制,使双馈风电系统为电网提供最大程度的无功支持,快速恢复电网电压。仿真实验结果表明,所提策略具有很高的节能控制性能。     

基于DSVPWM的PMSG并联型GS-NSC研究

为提高九开关变换器直流侧电压利用率,减少开关损耗,采用一种不连续空间矢量脉宽调制（DSVPWM）,同时将九开关变换器用于直驱式永磁同步风力发电机（PMSG）网侧构成并联型网侧九开关变换器（GS-NSC）。在对并联型GS-NSC控制策略、故障穿越方案进行理论分析的基础上,建立PMSG并联型GS-NSC仿真模型,设计多种电网电压故障工况对其进行仿真研究。结果表明,在电网电压正常工况下,并联型GS-NSC可维持电网电流的正弦波特性。在电网电压跌落工况下,并联型GS-NSC可向电网注入无功电流辅助电网电压的恢复,并通过提升并网电流幅值减少卸荷电路的功率损耗,降低PMSG散热负担。在电网电压骤升工况下,并联型GS-NSC可动态分配直流母线电压,避免因直流侧过压而导致PMSG退出运行。     

电网故障下直驱永磁风力发电机组机侧变流器改进控制策略

文章对电网电压跌落时的直驱永磁同步风力发电机组的低电压穿越过程进行深入研究,在电网电压跌落时,通过分析发电机机侧变流器最大风能跟踪控制策略,提出一种补偿q轴电流参考值抑制直流母线电压的新方法,并加入弱磁控制,使发电机输出功率迅速有效降低,进而维持机侧与网侧变流器的功率平衡及母线电压稳定。电网持续故障且超出规定时间时,为风电机组增加了卸荷电路,保证机组安全退出运行。分析结果验证了所提方案的正确性和有效性。     

基于改进网侧控制策略的半直驱风电系统FFRT研究

[目的]为改进半直驱风电系统的故障电压穿越（Flexible Fault Ride Through, FFRT）能力,提出采用电网故障时无功优先的改进网侧控制策略。[方法]在分析传统网侧控制策略的基础上,根据最新的故障电压穿越能力测试规程在传统网侧控制加入无功优先控制,在电网暂态故障期间优先向电网注入无功电流支撑电网电压恢复。根据改进网侧控制策略,对电网深度跌落和升高时采用卸荷电路结合改进网侧控制策略实现了风电机组的FFRT仿真运行,结合某项目6 MW半直驱风电机组,采用移动故障电压穿越测试设备进行故障电压现场测试。[结果]测试和仿真结果表明,改进网侧控制策略可提升半直驱风电系统的FFRT运行,无功电流稳定控制。[结论]改进网侧控制策略可在多种对称低电压/高电压故障工况和不对称高电压故障工况下优先向电网注入对应的稳定无功电流,有利于辅助电网电压恢复和提升半直驱风电系统的FFRT能力。     

一种新的双馈风力发电机的低电压穿越方案研究

结合励磁控制策略和硬件装置,提出一种新的双馈风力发电机低电压穿越运行方案。首先,通过分析双馈风力发电机系统模型的无源性,引入并改进无源性控制策略,提高转子电流的控制性能以应对电网电压小值跌落故障;然后在双馈风力发电机定子侧串入多抽头变压器,根据电网电压跌落程度检测,设计多路选择开关,保证发电机机侧电压始终维持在小值跌落范围内,从而提高双馈风力发电机的低电压穿越的能力。仿真结果表明:该方案既能改善电网电压小值跌落时对转子过电流控制性能,也能应对电网电压出现较严重的跌落情况。     

基于双环控制的双馈风力发电机组控制策略

在分析了双馈风力发电机组运行特性的基础上,提出一种基于双环控制的变换器控制策略。在转子侧,变换器采用定子磁链定向矢量控制技术,推导出了用转子有功电流和无功电流独立解耦控制有功功率和无功功率的策略,并实现了风能的最大跟踪;在电网侧,变换器采用电网电压定向矢量控制技术,构建了电流内环、电压外环的双闭环PI控制系统。利用PSCAD/EMTDC软件,构建了双馈风力发电机组仿真模型。仿真结果验证了所提控制策略的有效性和合理性     

Doubly-fed induction generator drive based WECS using fuzzy logic controller

The purpose of this paper is to improve the control performance of the variable speed, constant frequency doubly-fed induction generator in the wind turbine generation system by using fuzzy logic controllers. The control of the rotor-side converter is realized by stator flux oriented control, whereas the control of the grid-side converter is performed by a control strategy based on grid voltage orientation to maintain the DC-link voltage stability. An intelligent fuzzy inference system is proposed as an alternative of the conventional proportional and integral (PI) controller to overcome any disturbance, such as fast wind speed variation, short grid voltage fault, parameter variations and so on. Five fuzzy logic controllers are used in the rotor side converter (RSC) for maximum power point tracking (MPPT) algorithm, active and reactive power control loops, and another two fuzzy logic controllers for direct and quadratic rotor currents components control loops. The performances have been tested on 1.5 MW doubly-fed induction generator (DFIG) in a Matlab/Simulink software environment.     

Crowbar优化控制策略下的双馈风机无功调节能力研究

在分析双馈风机(DFIG)无功调节原理的基础上,根据最新的低电压穿越要求,建立优化的Crowbar控制策略,进而提出在电网严重故障期间内,Crowbar投入时由网侧变流器充当STATCOM为电网提供无功,Crowbar退出时无功输出继续由转子侧变流器励磁调节控制,推导出DFIG网侧及定子输出无功功率极限的表达式,结合优化的Crowbar控制策略研究DFIG的无功调节能力,最后利用RTDS平台进行仿真验证。结果表明,DFIG的无功调节能力与理论分析一致,在电网故障期间,应用此控制策略的DFIG可连续提供最大无功支持,且能帮助恢复电网电压。     

双馈感应式风力发电系统低电压运行特性研究

双馈感应发电机（DFIG）具有有功、无功功率独立调节能力及励磁变频器所需容量小等优点,在风力发电系统中得到越来越广泛的应用。但正是励磁变频器的过流能力限制使得其对电网故障非常敏感,电网故障下DFIG风电机组的控制能力受到限制。当前国外大多数风电并网标准都要求风力发电机在电网电压跌落的情况下不能从电网中解列,以便在故障后电网恢复过程中提供功率支持,避免发生后续更为严重的电网故障,这即是对风电机组低电压穿越能力的要求。为了保护变流器和对电网提供支撑,需要研制一种能够在电网故障发生时为故障电流进行旁路的设备——Crowbar电路。针对Crowbar的电流旁路装置进行了研究,说明Crowbar电路具有抑制转子浪涌电流和保护直流母线的作用,并在小功率平台上进行了试验,证明了这种设备对于提高DFIG系统的LVRT能力具有重要的作用。     

Comprehensive control strategy for a variable speed cage machine wind generation unit

A comprehensive control strategy, that addresses all three control objectives in a wind generation system, i.e. control of the local bus voltage to avoid voltage rise, capture of the maximum power in the wind and minimization of the power loss in the induction generator is proposed. The control signals are the desired current wave shapes (instantaneous three-phase currents) of the rectifier and the inverter in a double-sided PWM converter system connected between the wind generating unit and the grid. Studies performed on a complete model for a variable speed cage machine wind generation unit, including wind profile, wind turbine, induction generator, PWM converter, local load and transmission line, show that even as the wind speed changes randomly, the proposed control strategy leads the system to the optimum operating conditions.     

Application of energy capacitor system to wind power generation

In this paper, it is reported that energy capacitor system (ECS), which combines power electronic devices and electric double‐layer capacitor, can significantly decrease voltage and power fluctuations of grid‐connected fixed‐speed wind generator. The proper selection of wind farm output power reference is still a problem for smoothing the wind farm output power. This paper proposes exponential moving average to generate the reference output power of a grid‐connected wind farm. The objective of the control system is to follow the line power reference by absorbing or providing real power to or from the ECS. Moreover, the necessary reactive power can also be supplied to keep the wind farm terminal voltage at the desired reference level. Real wind speed data were used in the simulation analyses, which validate the effectiveness of the proposed control strategy. Simulation results clearly show that our proposed ECS can be suitable for wind power application. Copyright © 2007 John Wiley & Sons, Ltd.     

Analysis of reactive power strategies in HVDC‐connected wind power plant clusters

Offshore wind power plants (WPPs) built near each other but far from shore usually connect to the main grid by a common high‐voltage DC (HVDC) transmission system. In the resulting decoupled offshore grid, the wind turbine converters and the high‐voltage DC voltage‐source converter share the ability to inject or absorb reactive power. The overall reactive power control dispatch influences the power flows in the grid and hence the associated power losses. This paper evaluates the respective power losses in HVDC‐connected WPP clusters when applying 5 different reactive power control strategies. The case study is made for a 1.2‐GW–rated cluster comprising 3 WPP and is implemented in a combined load flow and converter loss model. A large set of feasible operating points for the system is analyzed for each strategy. The results show that a selection of simulations with equal wind speeds is sufficient for the annual energy production comparison. It is found that the continuous operation of the WPPs with unity power factor has a superior performance with low communication requirements compared with the other conventional strategies. The optimization‐based strategy, which is developed in this article, allows a further reduction of losses mainly because of the higher offshore grid voltage level imposed by the high‐voltage DC voltage‐source converter. Reactive power control in HVDC‐connected WPP clusters change significantly the overall power losses of the system, which depend rather on the total sum of the injected active power than on the variance of wind speeds inside the cluster.     

Compensation of network voltage unbalance using doubly fed induction generator-based wind farms

A control strategy for compensating AC network voltage unbalance using doubly fed induction generator (DFIG)-based wind farms is presented. A complete DFIG dynamic model containing both the rotor and grid side converters is used to accurately describe the average and ripple components of active/reactive power, electromagnetic torque and DC bus voltage, under unbalanced conditions. The principle of using DFIG systems to compensate grid voltage unbalance by injecting negative sequence current into the AC system is described. The injected negative sequence current can be provided by either the grid side or the rotor side converters. Various methods for coordinating these two converters are discussed and their respective impacts on power and torque oscillations are described. The validity of the proposed control strategy is demonstrated by simulations on a 30 MW DFIG-based wind farm using Matlab/Simulink during 2 and 4% voltage unbalances. The proposed compensation strategy can not only ensure reliable operation of the wind generators by restricting torque, DC link voltage and power oscillations, but also enable DFIG-based wind farms to contribute to rebalancing the connected network.     

DFIG sliding mode control fed by back-to-back PWM converter with DC-link voltage control for variable speed wind turbine

This paper proposes an indirect power control of doubly fed induction generator (DFIG) with the rotor connected to the electric grid through a back-to-back pulse width modulation (PWM) converter for variable speed wind power generation. Appropriate state space model of the DFIG is deduced. An original control strategy based on a variable structure control theory, also called sliding mode control, is applied to achieve the control of the active and reactive power exchanged between the stator of the DFIG and the grid. A proportional-integral-(PI) controller is used to keep the DC-link voltage constant for a back-to-back PWM converter. Simulations are conducted for validation of the digital controller operation using Matlab/Simulink software.     

New management structure of active and reactive power of a large wind farm based on multilevel converter

This paper proposes a system of supervision and operation of a new structure wherein a large wind farm is connected to an electrical grid. The farm is managed in such a manner that it can produce the power needed by the grid system. The supervision algorithm is used to distribute the active and reactive power references to the wind turbines proportionally. Based on the aerodynamic power and wind speed of each turbine, the active and reactive power references are produced individually. By using the vector field oriented control, each doubly fed induction generator is controlled through the rotor, which is connected to the two-level pulse width modulation converter. The close loop control is used to provide a constant DC voltage using a five-level neutral point clamped converter. The five-level neutral point clamped converter allows also the adaptation of the voltage level to the electrical grid with better resolution waveform. The analysis of the simulation results shows the effectiveness of the proposed system.