Low voltage ride through capability enhancement of wind turbine generator system during network disturbance

The energy capacitor system (ECS), composed of power electronic devices and electric double layer capacitor to enhance the low voltage ride through (LVRT) capability of fixed speed wind turbine generator system (WTGS) during network disturbance, is discussed. Control scheme of ECS is based on a sinusoidal pulse width modulation voltage source converter and DC?DC buck/boost converter composed of insulated gate bipolar transistors. Two-mass drive train model of WTGS is adopted because the drive train system modelling has great influence on the characteristics of wind generator system during network fault. Extensive analysis of symmetrical fault is performed with different voltage dip magnitudes and different time durations. Permanent fault because of unsuccessful reclosing is also analysed, which is one of the salient features of this study. A real grid code defined in the power system is considered and LVRT characteristic of WTGS is analysed. Finally, it is concluded that ECS (20 MW) can significantly enhance the LVRT capability of grid connected WTGS (50 MW) during network disturbance, where simulations have been carried out by using PSCAD/EMTDC.     

Improved particle swarm optimization for photovoltaic system connected to the grid with low voltage ride through capability

Grid connected photovoltaic (PV) system encounters different types of abnormalities during grid faults; the grid side inverter is subjected to three serious problems which are excessive DC link voltage, high AC currents and loss of grid-voltage synchronization. This high DC link voltage may damage the inverter. Also, the voltage sags will force the PV system to be disconnected from the grid according to grid code. This paper presents a novel control strategy of the two-stage three-phase PV system to improve the Low-Voltage Ride-Through (LVRT) capability according to the grid connection requirement. The non-linear control technique using Improved Particle Swarm Optimization (IPSO) of a PV system connected to the grid through an isolated high frequency DC–DC full bridge converter and a three-phase three level neutral point clamped DC-AC converter (3LNPC²) with output power control under severe faults of grid voltage. The paper, also discusses the transient behavior and the performance limit for LVRT by using a DC-Chopper circuit. The model has been implemented in MATLAB/SIMULINK. The proposed control succeeded to track MPP, achieved LVRT requirements and improving the quality of DC link voltage. The paper shows superiority of IPSO than Incremental Conductance (IC) method during MPPT mode of PV system.     

Low voltage ride through of doubly-fed induction generator connected to the grid using sliding mode control strategy

Wind Energy Conversion System (WECS) based on Doubly Fed Induction Generator (DFIG) connected to the grid is subjected to high transient currents at rotor side and rise in DC-link voltage during voltage sag at stator/grid side. To secure power system operation wind turbines have to meet grid requirements through the Low voltage ride through (LVRT) capability and contribute to grid voltage control during severe situations. This paper presents the modeling and control designs for WECS based on a real model of DFIG taking into account the effect of stator resistance. The non-linear control technique using sliding mode control (SMC) strategy is used to alter the dynamics of 1.5 MW wind turbine system connected to the grid under severe faults of grid voltage. The paper, also discusses the transient behavior and points out the performance limit for LVRT by using two protection circuits of an AC-crowbar and a DC-Chopper which follow a developed flowchart of system protection modes under fault which achieved LVRT requirements through results. The model has been implemented in MATLAB/SIMULINK for both rotor and grid side converters.     

Reliability analysis of grid connected small wind turbine power electronics

Grid connection of small permanent magnet generator (PMG) based wind turbines requires a power conditioning system comprising a bridge rectifier, a dc–dc converter and a grid-tie inverter. This work presents a reliability analysis and an identification of the least reliable component of the power conditioning system of such grid connection arrangements. Reliability of the configuration is analyzed for the worst case scenario of maximum conversion losses at a particular wind speed. The analysis reveals that the reliability of the power conditioning system of such PMG based wind turbines is fairly low and it reduces to 84% of initial value within one year. The investigation is further enhanced by identifying the least reliable component within the power conditioning system and found that the inverter has the dominant effect on the system reliability, while the dc–dc converter has the least significant effect. The reliability analysis demonstrates that a permanent magnet generator based wind energy conversion system is not the best option from the point of view of power conditioning system reliability. The analysis also reveals that new research is required to determine a robust power electronics configuration for small wind turbine conversion systems.     

基于电池储能和Crowbar的风力发电机低电压穿越控制的研究

文章提出一种基于电池储能和Crowbar协调控制提高DFIG的LVRT能力的策略。在系统电压小幅跌落时,电池储能系统,通过PQ解耦PI控制,适当调节交流侧输出电压幅值和相位,以提供满足系统电压稳定的无功功率;当系统电压大幅跌落时,电池储能协同Crowbar电路的投切控制,及时卸荷多余能量并保护变流器,保证DFIG在故障期间不脱网运行。在PSCAD/EMTDC平台对本文提出的控制策略进行仿真,结果表明本文的控制策略能在系统电压在大幅深度跌落情况下,使DFIG具备LVRT能力。     

风电场低电压穿越测试方法对比研究

随着风电接入电网的比例增大,对电网安全稳定性的影响不容忽视,应避免因风电脱网造成大面积停电事故。根据国家电网公司对风力发电机组低电压穿越专项检查的开展,各省公司结合自身情况,开展低电压穿越抽检测试工作。本文结合辽宁省电力有限公司电力科学研究院低电压穿越测试成果,介绍设备测试及人工短路试验测试两种方法,并进行对比研究,为更好、更快地进行低电压穿越测试工作提供宝贵的经验,同时确保电网安全稳定运行。     

Analysis of the turbine standstill for a grid connected wind farm (case study)

In the present paper, several types of collected data were employed to analyse the causes of turbines shutdown in a grid-connected wind farm. Although the average availability of the considered wind farm exceeds 96%, the individual availability of some turbines does not exceed 92%. In this context, the present paper introduces a novel approach of understanding the turbine standstill and availability calculation. This approach is based on a variation of monthly energy production to weight the shutdown time including the maintenance and fault hours. The calm hours in summer are 60% less than the average calm time for the considered wind farm. The distribution of inoperative hours reveals a 300% difference between the original and weighed times of downtime. On the other hand, weighed times are used to assess the impact of various faults causing turbines shutdown. The frequency distribution of the faults has shown that 42% of turbine shutdowns are caused by network disturbances, 70% of them are attributed to grid disconnections. Finally, the time distribution of the network faults is investigated to illustrate their impact on the turbine standstill.     

风电机组低电压穿越能力影响因素分析与实例

我国风电大规模汇集地区多处于电网末端,电压波动性强,随着对风电并网安全的关注和风电机组并网性能要求的提高,低电压穿越能力已成为衡量风电机组并网性能的重要指标。文章调研了同一区域内多个风电场实际运行中的低电压穿越故障情况,分析了整机制造厂家、高校及相关研究机构对风电机组低电压穿越技术的研究现状。通过分类统计测试过程中遇到的风电机组低电压脱网故障和总结56台风电机组的低电压穿越测试结果,分析了造成风电机组低电压穿越能力不足的原因,并对引起风电机组低电压穿越能力不足的影响因素进行了阐述。目前,软件版本控制、保护定值的设置与管理、硬件的维护水平已经成为并网风电机组低电压穿越能力的主要影响因素。     

A review of fault ride through of PV and wind renewable energies in grid codes

This paper presents a comprehensive review of fault ride through (FRT) in the grid code of 38 selected countries with an emphasis on renewable energy (REN) sources–related rules. Grid codes are the rules legislated usually by the transmission system operators (TSOs) to determine the grid integration requirements of electrical power generators. Each country establishes its grid code for satisfying the minimum required technical criteria and revises it frequently to cope with new modifications of the utility. Growing the penetration of REN sources have influenced many operational aspects of the power system such as protection, power quality, reliability, and stability. Thereupon, regulations must ensure the power system's secure and controllable operation of REN sources. FRT is one of the main parts of the grid code, and its characteristics affect the performance and rating of power system apparatus. FRT defines the performance of electric power generators during and in postfault conditions. FRT of solar photovoltaic (PV) and wind turbines (WTs) as the main REN sources of energy has great importance in the grid codes. In this paper, a comparison of FRTs in the grid code of 38 countries, including low‐voltage ride through (LVRT), zero‐voltage ride through (ZVRT), and high‐voltage ride through (HVRT) are provided and surveyed.     

Fault ride through of fully rated converter wind turbines with AC and DC transmission

Fault ride through of fully rated converter wind turbines in an offshore wind farm connected to onshore network via either high voltage AC (HVAC) or high voltage DC (HVDC) transmission is described. Control of the generators and the grid side converters is shown using vector control techniques. A de-loading scheme was used to protect the wind turbine DC link capacitors from over voltage. How de-loading of each generator aids the fault ride through of the wind farm connected through HVAC transmission is demonstrated. The voltage recovery of the AC network during the fault was enhanced by increasing the reactive power current of the wind turbine grid side converter. A practical fault ride through protection scheme for a wind farm connected through an HVDC link is to employ a chopper circuit on the HVDC link. Two alternatives to this approach are also discussed. The first involves de-loading the wind farm on detection of the fault, which requires communication of the fault condition to each wind turbine of the wind farm. The second scheme avoids this complex communication requirement by transferring the fault condition via control of the HVDC link to the offshore converter. The fault performances of the three schemes are simulated and the results were used to assess their respective capabilities.     

考虑变直流母线电压参考值的直驱风电机组高电压穿越控制策略

针对风电机组高电压脱网问题,提出了一种考虑变直流母线电压参考值与网侧无功优先控制相结合的HVRT控制策略。该策略在电压轻度骤升时,通过优化无功电流给定值,快速向故障电网注入感性无功电流;电压深度骤升时,改变直流母线电压参考值,抑制直流侧电压波动。最后,在Simulink中搭建了1.5 MW直驱永磁风电机组仿真模型,在不同电压骤升幅度下对文章所提控制策略进行验证,结果表明,该控制策略能在不同电压骤升幅度下实现机组的HVRT,且避免Chopper电路的频繁动作,提高了机组稳定运行的能力。     

运用STATCOM解决风电场LVRT问题的控制措施研究

随着风力机组装机容量的增加,电网出现故障导致电压跌落后,机组如果解列将会导致系统暂态不稳定、低电压穿越(LVRT)的问题逐渐引起人们的广泛关注。文章分析了云南雷应山风电场部分风机脱网事件产生原因,在此基础上提出了建立电网电压跌落时双馈异步机组(DFIG)的数学模型以及静止同步补偿器(STATCOM)应用于风电场的控制模型,并在Matlab/Simulink中对基于DFIG的风电场和STATCOM进行建模。研究结果表明,STATCOM在电网发生单相接地故障时能够帮助风电场快速的重建电压,确保风电机组连续运行。     

基于反馈线性化技术的直驱永磁同步风电机组低电压穿越研究

通过对直驱永磁同步风电系统的研究,提出了一种基于反馈线性化的低电压穿越控制策略。直流母线电压由发电机侧整流器来维持调节,考虑到直流母线电压和发电机转子转速的非线性关系,直流母线电压的控制采用了反馈线性化技术。网侧逆变器根据最大风能跟踪原则来控制网侧有功功率,并加入了转子速度参考值的判定环节。运用PSCAD仿真平台建立了一个2 MW的直驱永磁同步风电系统,验证了其正确性和有效性。     

A modular series connected converter structure suitable for a high‐voltage direct current transformerless offshore wind turbine

A modular generator/converter system suitable for a 100 kV transformerless HVDC offshore wind turbine is analyzed in this paper. The large diameter generator combined with mechanical tolerances may result in substantial parameter deviations. Therefore, the impact of such parameter variations is analyzed. A steady‐state model relating these variations to the imbalances between module DC voltages has been developed. Additionally, the impact of different control strategies was assessed through simulations in EMTDC/PSCAD. Finally, experimental verification of the system performed on a 45 kW laboratory prototype is presented. The theory is developed with the transformerless wind turbine concept in mind but is also applicable to other similar series connected converter topologies.Copyright © 2013 John Wiley & Sons, Ltd.     

基于自适应模型预测的风电场低压穿越控制机制研究

风电场并网需满足并网导则的电压要求,双馈型风电场的无功功率输出主要来源于风力发电机网侧换流器、风力发电机定子和静态同步补偿器,因此在风电并网过程中,特别是低压穿越过程中,须要调节三者的无功功率输出,来保证风力发电机并网的可靠性。文章在建立无功功率调节方式数学模型的基础上,实现低压穿越过程中3种无功补偿方法的协同参与,并利用自适应模型控制风力发电机的定子。此外,根据电压的跌落情况,确定风力发电机网侧换流器和静态同步补偿器的无功功率输出,进而确定风力发电机定子控制过程中的最优化跟踪目标函数,以实现多种无功功率调节方式的协同参与。最后,利用风电场单机等值模型仿真结果对自适应模型预测方法进行验证。分析结果表明,相比于传统模型预测控制方法,采用自适应模型预测控制方法后,风电场静态同步补偿器的输出功率减小了14%。     

Intelligent hybrid power generation system using new hybrid fuzzy-neural for photovoltaic system and RBFNSM for wind turbine in the grid connected mode

Photovoltaic (PV) generation is growing increasingly fast as a renewable energy source. Nevertheless, the drawback of the PV system is intermittent because of depending on weather conditions. Therefore, the wind power can be considered to assist for a stable and reliable output from the PV generation system for loads and improve the dynamic performance of the whole generation system in the grid connected mode. In this paper, a novel topology of an intelligent hybrid generation system with PV and wind turbine is presented. In order to capture the maximum power, a hybrid fuzzy-neural maximum power point tracking (MPPT) method is applied in the PV system. The average tracking efficiency of the hybrid fuzzy-neural is incremented by approximately two percentage points in comparison with the conventional methods. The pitch angle of the wind turbine is controlled by radial basis function network-sliding mode (RBFNSM). Different conditions are represented in simulation results that compare the real power values with those of the presented methods. The obtained results verify the effectiveness and superiority of the proposed method which has the advantages of robustness, fast response and good performance. Detailed mathematical model and a control approach of a three-phase grid-connected intelligent hybrid system have been proposed using Matlab/Simulink.     

In fault ride through reactive current rise time requirements of various European grid codes—analysis based on a full‐converter wind turbine

The European transmission system operators specify grid codes to ensure a safe and reliable operation of the electrical power system, even during grid faults. Wind power plants have to comply with such specific requirements prior to installation and operation. Some of the requirements, however, are open to interpretation, especially because of lack of specification, and therefore, they pose technical challenges to full‐converter wind turbines. In fact, different interpretations leave it open to debate on whether a requirement can be fulfilled or not. The rise time requirement across some European grid codes is discussed in this paper. First the uncertainties in some transmission system operators' definitions of rise time, step response time and settling time are presented, and then a comparative analysis is performed among calculation methods, such as instantaneous reactive current in alpha‐beta reference frame, direct and quadrature reference frame and root mean square of the positive sequence component. The comparison results of both ideal cases and randomly selected measurements from actual full‐converter wind turbine field tests show that the rise time of the reactive current is significantly affected by the calculation methods. This effect in some cases can make the difference between fulfilling the requirement or not. As a result of that, it is highlighted in this paper the need for a common understanding of the rise time requirements between industry and system operators, based on clear technical fundamentals. Copyright © 2015 John Wiley & Sons, Ltd.     

基于DSP实现风力发电机组并网运行

提出了一种风力发电机组并网运行系统;研究了基于数字信号处理器-DSP(TMS320F240)控制的发电机转速驱动控制系统;详细介绍了该系统的DSP控制器的硬件电路设计,实现了对发电机转轴的速度检测和滑差离合器励磁线圈的电流检测;最后给出了该系统的软件设计方案及控制策略,完成对整个系统的控制,使发电机转速稳定,且输出稳定的频率和电压.     

某风电场风力发电机组故障诊断

为了准确判断风电机组的运行状态及故障,提出了基于常规分析—振动幅值分析—波形频谱分析的故障诊断流程,阐述了针对风电机组的幅值分析方法和波形频谱分析方法,并通过对某机组异响的根源探究实例,准确地诊断出机组异响来源于齿轮箱太阳轮,可为风电机组故障诊断技术提供依据。