基于PSCAD的双馈感应式风力发电系统低压穿越能力仿真研究

在电网故障条件下,风电并网导则要求风电发电机具备低压穿越能力。为了保护发电机及其变流器,DFIG需要采用Crowbar保护电路为转子过电流提供旁路通道,同时抑制直流母线过电压。本文在PSCAD平台下搭建了2MW双馈感应式风力发电系统,并对有无Crowbar电路的DFIG在三相短路条件下进行了仿真。结果表明：具备Crowbar电路的DFIG有较好的暂态特性,并且具各较强的低电压穿越能力。     

A grid-tie PV inverter with the ability to improve power quality under unbalanced and distorted source voltage conditions

ABSTRACT

This paper proposes a grid-tie PV inverter that is able to improve power quality under conditions of both distorted and unbalanced source voltage. The presented strategy is based on the instantaneous power theory and uses a second-order generalized integrator-quadrature signal generator (SOGI-QSG). The presented control strategy is aimed at compensating reactive power, eliminating current harmonics, load balancing, and enabling the PV to inject maximum power to the grid. The advantages of the control system are the use of SOGI-QSG adaptive filter and frequency-locked loop (FLL), and removing the low-pass filter and phase-locked loop (PLL). DC–DC and DC–AC converters are utilized for connecting the PV to the grid. The DC–DC and DC–AC converters are responsible for maximum PV power tracking and achieving the control aims, respectively. Using 4-leg converter structure for grid-tie inverter enables achieving the control objectives in 3-phase 4-wire distribution network without any transformer. The presented control strategy is applied to a 3-phase 4-wire distribution network and is simulated in MATLAB/SIMULINK environment. The results of this simulation are then compared with the conventional instantaneous power method in areas including load balancing, reactive power compensation and the elimination of current harmonics, under unbalanced and distorted source voltage conditions.     

Advanced control for PWM converter and variable-speed induction generator

The paper describes a simple control structure for a vector-controlled stand-alone induction generator (IG) used to operate under variable speeds. Deadbeat current control is developed for a voltage source PWM converter and the three-phase variable speed squirrel-cage IG to regulate DC-link and generator voltages with newly designed phase-locked-loop circuit. The required reactive power for the variable-speed IG is supplied by means of the PWM converter and a capacitor bank to build up the voltage of the IG without the need for a battery and to reduce the rating of the PWM converter with the need for only three sensors. This proposed scheme can be used efficiently for variable speed wind or hydro energy conversion systems. The measurements of the IG system at various speeds and loads are given and show that this proposed system is capable of good AC and DC voltages regulation     

Perspectives of China’s Wind Energy Development

Wind energy is a kind of clean renewable energy, which is also relatively mature in technology, with large-scale development conditions and prospect for the commercialization. Wind energy’s development and utilization is an important measure to increase energy supply, adjust energy structure, ensure energy security, protect the ecological environment, reduce greenhouse gas emission and build a harmonious society. Wind energy is a kind of clean renewable energy, which is also relatively mature in technology, with large-scale development conditions and prospect for the commercialization. The development of wind energy is a systematic project, involving policy, law, technology, economy, society, environment, education and other aspects. The relationship among all the aspects should be well treated and coordinated. This paper has discussed the following relationships which should be well coordinated: relationship between wind resources and wind energy development, relationship between the wind turbine generator system and the components, relationship between wind energy technology and wind energy industry, relationship between off-grid wind power and grid-connected wind power, relationship between wind farm and the power grid, relationship between onshore wind power and offshore wind power, relationship between wind energy and other energies, relationship between technology introduction and self-innovation, relationship among foreign-funded, joint ventured and domestic-funded enterprises and relationship between the government guidance and the market regulation, as well as giving out some suggestions.     

含不同机组风电场低电压穿越能力仿真研究

在PSCAD/EMTDC仿真环境下建立双馈风力发电场及恒速恒频风力发电场交流并网仿真模型,通过交流系统三相短路故障仿真,研究对比2种不同风力发电机组的低电压穿越能力。仿真得出恒速恒频风力发电机组避免飞车的极限切除时间,故障持续时间小于极限切除时间便可维持恒速恒频风力发电机组的稳定不脱网运行。通过在不同点设置短路故障对比得出,故障点距离风电场电气距离越远,风电场低电压穿越能力越强。     

Wind-driven stand-alone DFIG with battery and pumped hydro storage system

A wind-driven doubly fed induction generator (DFIG) along with the battery and pumped hydro storage plant (PHSP) has been devised for supplying isolated loads. PHSP-based storage system is economical and viable for the MW level wind-turbine system. The proposed scheme employs a squirrel-cage induction machine (SCIM) coupled with reversible pump turbine for PHSP. The battery storage is also included in this system to cope up with the intermittent nature of wind and fast-changing load. A simple control strategy has been implemented for maintaining the set values of voltage magnitude and frequency at the stator terminals of DFIG, which serve as a virtual grid for connecting ac loads and SCIM. Based on the availability of power in the wind, PHSP and battery, various operating modes of the proposed system have been clearly identified for supplying the isolated loads. These operating modes are clearly demonstrated through the analysis developed for this purpose and validated through experimental results. The salient features of the proposed system over the existing stand-alone wind-driven generators are (i) structural simplicity, i.e., employing only one power electronic converter, (ii) wide speed operation of wind-driven DFIG, (iii) reduced battery capacity, (iv) high energy storage using PHSP and (v) availability of continuous power to the isolated loads.     

Voltage and frequency control of parallel operated synchronous generator and induction generator with STATCOM in micro hydro scheme

Parallel operation of synchronous and induction generators in micro hydro scheme is presented. The synchronous generator has an exciter, which provides a fixed excitation to produce normal rated terminal voltage at full resistive load. On the other hand, the induction generator has neither exciter nor speed controller. Static compensator (STATCOM) is connected to the common bus for terminal voltage and frequency control. A resistive dump load is connected across the DC link capacitor of STATCOM through a chopper to control active power. Simulink model is developed to perform transient analysis of the proposed scheme. Experimental results are presented to compare with the simulation results. It is found that connection of an induction generator in parallel with the synchronous is much simpler than connecting two synchronous generators in parallel.     

Modelling and validation of a squirrel cage induction generator wind turbine during connection to the local grid

The increasing penetration of wind turbine generators (WTGs) into power systems can affect many network operational aspects such as stability and power quality. The accurate, validated representation of these generators and their components for studying particular operational events, such as cut-in and soft-starting, short-circuit faults and generator switching, remains a challenge. Accurate simulation is particularly important for investigating stability interactions within weak grids or localised networks (e.g. micro-grids or islanded networks). One of the events producing major transient interaction between a WTG and a local grid is the grid connection itself. A simulation model of the use of a soft-starter during the grid connection of a wind turbine equipped with a squirrel cage induction generator and thyristor-based soft-start module is presented. This model has been validated using experimental measurements taken from a wind turbine generator in an operational wind farm site. The analysis focuses on verifying the transients produced during the short-time after the connection to the local grid. Existing literature presents insufficient details about this particular process as well as the practical performance of the soft-starter. It is further demonstrated that ambiguities in this subject may lead to mistaken conclusions in technical assessments carried out by wind farm operators and distribution network operators (DNOs).     

考虑RNA运行作用的近海风电结构动力响应分析

在风、浪的长期耦合作用下,海上风电结构的振动问题不仅会影响发电机组的电能输出,还会加剧结构的累积疲劳损伤,危害结构安全。为更加科学、合理地认识近海风电结构的动力特性,该文通过考虑风轮-机舱组件(rotor-nacelle assembly, RNA)运行作用及风、浪相关性,采用Von Karman风谱模型模拟湍流风场并计算气动荷载,通过莫里森方程求取单桩基础结构的波浪荷载,对NREL 5MW单桩风电塔进行动力响应分析,对比其在不同状态下的动态行为模式;通过批处理程序,开展对近海风电结构在3 m/s~30 m/s风速范围内的响应计算,探究RNA运行作用下近海风电结构位移、加速度响应随风速的变化规律。结果表明:近海风电结构在不同工作状态下的动力响应具有不同的频谱特征,其位移、加速度峰值响应会被RNA运行作用放大。     

潮流分析和鸟群优化在风水协同运行中的应用

风力发电的随机性导致弃风。考虑在实际发电约束以及电网络约束条件下,运用水电的调峰调频特性,最大化平抑风电出力的波动性,使风电出力与水电出力之和按照计划输出,将风电处理成可供电力系统实施调度计划的稳定发电节点。为了提高风水协同发电总输出功率平稳性,提出了基于鸟群算法的风水协同运行控制方法。在控制系统寻优前进行系统潮流计算,在保证系统潮流安全条件下,有效地控制水轮机组出力,快速追踪期望输出功率。算例验证了上述方法的有效性,并且分析了高弃风惩罚和高功率波动惩罚对风电水电协同运行的影响。     

敏感用户高品质交-直流级联供电方案研究

工业过程中大量使用的变频器(variable frequency drive,VFD)在采用传统交流供电时易受到电压暂降影响,传统治理方式存在检测延时、控制复杂等问题。为此,该文从敏感负荷变频器在电网扰动工况下的供电需求量化出发,围绕供电拓扑设计、DC/DC变换器的控制策略及储能单元容量配置等方面,构建一种实用化工业用交-直流级联供电方案。该文利用电压暂降过程中直流供电回路与敏感负荷间的压差自感应控制,实现交-直流供电回路无扰动切换,提高电压暂降治理响应的快速性;采用两相交错并联DC/DC变换器接入集中式储能,减少储能系统纹波系数,并给出两相均流控制方法。最后,通过Matlab/Simulink中的建模仿真与样机的实验测试,验证所提方案能够在交流系统发生不同严重程度电压暂降过程中为各类敏感负荷提供稳定的连续供电,为解决工业敏感用户高品质供电问题提供可实用的新思路。     

A Modular Superconducting Generator for Offshore Wind Turbines

In this study, a new claw-pole type transverse flux superconducting generator topology is presented. The machine has a stationary superconducting field winding, which eliminates electrical brushes and cryocouplers. The machine is specifically designed for low-speed high torque applications such as large offshore wind turbines. The proposed machine is robust and has a modular structure. A 30 kW, 100 rpm prototype is planned to be manufactured to prove the concept. MgB2, YBCO, and BSSCO wires are compared in terms of wire length, operating temperature, and critical temperature. The magnetic flux penetrating into superconducting wire has been simulated using 3D FEA software. Moreover, mechanical loads are estimated and the deflections in the structure are analysed.     

基于RF和ANFIS算法的直驱风电机组故障预警

针对风电机组运行工况复杂和单一状态参数不能较好实现故障早期预警的特点,提出随机森林算法(RF)和自适应模糊神经网络算法(ANFIS)相结合的故障预警方法。该方法充分考虑机组运行数据高维非线性特点,应用随机森林算法,建立有功功率与运行参数的数据驱动模型,计算各运行参数影响有功功率的相关度;构建自适应网络模糊推理系统模型,以训练误差最大值作为故障预警阈值,实时监测发电机运行状态。将该方法应用于某1.5 MW直驱机组发电机故障预警分析,结果表明,该方法能够提前预警发电机健康状态,避免严重事故发生,对风电场开展预防性维护、维修具有重要的指导意义。     

锯齿降噪结构在风力发电机组叶片上的应用

基于IEC61400-11风力发电机组噪声测试标准,应用NI硬件和LabView软件搭建噪声测试系统,对某3.0 MW风力发电机组叶片加装锯齿降噪结构前后的噪声辐射值进行现场测试,通过对比4 m/s～8 m/s风速区间的测点噪声值和1/3倍频程频谱数据,研究锯齿结构在大型风力发电机组叶片上的应用效果。研究结果表明,在叶片上安装锯齿降噪结构可显著降低机组在5 m/s～6 m/s风速区间运行时的噪声,对高风速区间内的低频段噪声也有明显降噪效果。     

上海东海大桥海上风电场规划建设关键技术研究

通过对上海东海大桥海上风电场的选址、风电场升压方式、基础选型设计、桩基试验、基础施工、风机安装等技术问题的研究和实践,提出了海上风电场选址原则、接入电网方式、具有防撞能力的高桩混凝土承台基础形式、风机基础结构分析方法、桩的承载力试验手段、高桩承台施工和风机整体吊装方案等,为海上风电场规划建设提供借鉴。     

Stealth technology for wind turbines

Currently, a large proportion of proposed UK wind farms have either concerns raised at the pre-planning stage or formal objections made by radar operators on the basis of the potential for wind turbines to cause interference to radar systems. The current generation of on and off-shore three-bladed horizontal axis wind turbines have radar signatures consistent with their often very large physical size and hence considerable potential to reduce the ability of ground-based radars to detect targets in the vicinity of the farm. The impact of wind farms, particularly on ground-based aviation radars such as those operated for air defence and military and civil air traffic control purposes is likely to become particularly acute as European Union member governments strive to meet the requirements for energy generation under the Renewables Obligation. In addition, the increasing number of offshore wind farm projects proposed has the potential to cause interference to marine radars such as coastal vessel traffic services and those on-board vessels for navigational purposes. This study considers the options available for the reduction of turbine radar signature and presents solutions for each of the main external turbine components. The radar signature reduction approaches are based on existing technologies developed for aerospace stealth applications. However, the realisation of these for the purposes of reducing wind turbine radar signatures is a novel development, particularly in the solutions proposed. The reduction of wind turbine-induced radar interference is a growing area of research.     

大规模新能源集中外送系统源网协调风险及仿真评估

大规模新能源集中外送系统新能源占比高、耐受直流故障扰动冲击能力低,在源网协调方面存在较为突出的问题。该文分析了我国大规模新能源集中外送系统主要的风险隐患,包括电压波动、频率波动和低频振荡问题。指出大规模新能源集中外送系统源网协调仿真评估的建模重点,包括励磁系统辅助控制环节、发电机涉网保护、含动力系统的发电机调速控制精细化建模等方面。提出了大规模新能源集中外送系统源网协调仿真评估流程及注意事项,可为实际电网源网协调提供参考。     

Space and time harmonics related problems and their mitigation for position and speed sensorless slip-ring induction motor drives applications

There have been renewed interests in slip-ring induction machines due to their increasing use in both grid connected and stand-alone wind power generation schemes. Despite the squirrel cage induction generators’ advantages of being brushless, low-cost, needing less maintenance and having inherent overload protection, the biggest advantage of variable-speed wound rotor induction machines is in its doubled energy capture. Also in high power induction motor drives such as static Kramer drives or static Scherbius drives use of wound rotor induction motors is a must. Thus it becomes necessary to measure the speed of the machine for closed loop control for such high performance drives. Recently, a sensorless position and speed estimation scheme was proposed for wound rotor wind power generator. In this paper, the limitation of the scheme caused by space and time harmonics have been investigated. Simulation results have been presented to explain the mechanism of the space and time harmonics caused distortion of current. Experimental results showing the deterioration of speed detection scheme at light load for a slip-ring induction motor have been presented. Finally, improvements have been applied experimentally to obtain better speed estimation.     

Greedy robust wind farm layout optimization with feasibility guarantee

This article proposes a method with light data requirements for generating robust wind farm layouts. Robustness in this work is quantified as the lowest energy conversion efficiency of the wind farm across all wind directions. A quadratic integer programming formulation for generating robustness-maximizing layouts is presented. Small instances of the proposed formulation can be solved to optimality using branch and bound. A modified greedy algorithm that guarantees solution feasibility with regards to inter-turbine safety distance is proposed to find solutions to larger problem instances. A series of experiments were conducted using real world wind data collected at two sites to demonstrate the trade-offs in power generation between robust layouts and power output maximizing layouts. The results show a loss of around 1.1% in hourly power generation in return for an increase in minimum power output of 1% to 45% across all directions for robust layouts generated in the experiments. The increase in robustness largely depends on the shape and orientation of the wind farm relative to the dominant wind direction, as well as the difference between the average wind speed at the site of the wind farm and rated wind speed of the turbines.     

Design and analysis of dynamic voltage restorer for deep voltage sag and harmonic compensation

A dynamic voltage restorer (DVR) to compensate deep voltage sags and harmonics is proposed. The DVR consists of shunt and series converters connected back-to-back through a DC-to-DC step up converter. The presence of the DC-to-DC step converter permits the DVR to compensate deep voltage sags for long duration. The series converter is connected to the supply side whereas the shunt converter is connected to the load side. With this configuration, there is no need for large DC capacitors. A design procedure for the components of the DVR is presented under a voltage sag condition. The control system of the proposed DVR is based on hysteresis voltage control. Besides voltage sag compensation, the capability of compensating load voltage harmonics has been added to the DVR to increase the power quality benefits to the load with almost negligible effect on the sag compensation capability. The proposed DVR is modelled and simulated using SIMULINK/MATLAB environment. Time domain simulations are used to verify the operation of the DVR with linear and non-linear loads.