An Adaptive Nonlinear Controller for DFIM-Based Wind Energy Conversion Systems

An adaptive nonlinear controller for wind energy doubly fed induction machines is introduced in this paper. The proposed controller is based on the feedback linearization technique and includes a disturbance observer for estimation of parameter uncertainties. Estimated uncertainties values are injected in order to construct the control law, improving in this way the system's performance. The controller behavior, when tracking power references, is tested with realistic Electromagnetic Transients for dc /Power Systems Computer-Aided Design simulations. In addition, the controller performance is checked in the presence of parameter uncertainties and nearby faults.      

An analysis of the potential of Wind Energy Conversion Systems

Wind Energy Conversion Systems (WECS) are solar systems because the sun drives the atmospheric circulation. About 20 TW of wind energy flows poleward annually, over land in temperate latitudes, in the 500 m deep atmospheric boundary layer. An average 500 GW of electricity could be generated by massive exploitation of the U.S. Great Plains wind field.There are, however, large fluctuations in available wind power. There are frequent 20% variations in annual supply; annual periodicity brings most wind power during the spring; there are storm cycles; and there is a diurnal cycle. Gusts and turbulence also require filtering to meet normal power requirements. Several schemes are evolving to tame this erratic wind power supply.Modern technology is refining horizontal-axis turbines of a wide size range. Progress is also being made toward producing an economical vertical-axis turbine. Standards for turbine performance evaluation and installation site selection are now being developed. Yet it will be a few years before proven systems can significantly affect national energy supplies.Eventually, mass-produced WECS may cost $1000 per installed, rated kW, but the wind does not often flow at turbine-rated speed. With some storage or filtering, problems with wind variability may be overcome. Then WECS electricity production may be as economical as other electric generators. No serious hazards or environmental impacts should slow WECS development.     

Sliding Mode Power Control of Variable-Speed Wind Energy Conversion Systems

This paper addresses the problem of controlling power generation in variable-speed wind energy conversion systems (VS-WECS). These systems have two operation regions depending on the wind turbine tip-speed ratio. They are distinguished by minimum phase behavior in one of these regions and a nonminimum phase in the other one. A sliding mode control strategy is then proposed to ensure stability in both operation regions and to impose the ideal feedback control solution despite model uncertainties. The proposed sliding mode control strategy presents attractive features such as robustness to parametric uncertainties of the turbine and the generator as well as to electric grid disturbances. The proposed sliding mode control approach has been simulated on a 1.5-MW three-blade wind turbine to evaluate its consistency and performance. The next step was the validation using the National Renewable Energy Laboratory (NREL) wind turbine simulator called the fatigue, aerodynamics, structures, and turbulence code (FAST). Both simulation and validation results show that the proposed control strategy is effective in terms of power regulation. Moreover, the sliding mode approach is arranged so as to produce no chattering in the generated torque that could lead to increased mechanical stress because of strong torque variations.     

Hybrid Control of a Grid-Interactive Wind Energy Conversion System

Without storage provision, a wind energy conversion system (WECS) does not have fault ride-through capability for most temporary faults on the utility feeder. This paper proposes a hybrid valve switching and control strategy for a voltage-sourced converter (VSC) used for interfacing a WECS to the utility grid. The hybrid control of the VSC ensures continuous operation of the system in the presence of temporary single line to ground faults on the utility feeder without the need for a storage provision. The fast acting hybrid control also limits reactive fault current contribution by the converter, and therefore, avoids problems associated with overcurrent protection of the feeder. The hybrid valve switching and control of the VSC consists of: 1) sinusoidal pulse width modulation (SPWM) based valve switching and current-controlled voltage-source operation of the VSC during normal system operating conditions and 2) hysteresis space vector modulation (HSVM) based switching together with controlled current-source operation of the VSC during temporary fault conditions. The hybrid control of the VSC isolates the WECS from the grid side disturbances to ensure uninterrupted operation of the unit. Simulation studies of the grid-interactive WECS in PSCAD/EMTDC confirm the validity of the proposed hybrid control scheme.      

An Electrical Approach to Mechanical Effort Reduction in Wind Energy Conversion Systems

A strategy for controlling wind farms composed of variable-speed machines is considered in this paper. It is shown that mechanical efforts produced by wind gusts on individual machines can be reduced by means of a supplementary control signal coming from a centralized controller. This is done while the total wind farm power output is kept at the same value as in the absence of the proposed controller.      

Voltage and Frequency Controller for a Three-Phase Four-Wire Autonomous Wind Energy Conversion System

This paper deals with control of voltage and frequency of an autonomous wind energy conversion system (AWECS) based on capacitor-excited asynchronous generator and feeding three-phase four-wire loads. The proposed controller consists of three single-phase insulated gate bipolar junction transistor (IGBT)-based voltage source converters (VSCs) and a battery at dc link. These three single-phase VSCs are connected to each phase of the generator through three single-phase transformers. The proposed controller is having bidirectional flow capability of active and reactive powers by which it controls the system voltage and frequency with variation of consumer loads and the speed of the wind. VSCs along with transformer function as a voltage regulator, a harmonic eliminator, a load balancer, and a neutral current compensator while the battery is used to control the active power flow which, in turn, maintains the constant system frequency. The complete electromechanical system is modeled and simulated in the MATLAB using the Simulink and the power system blockset (PSB) toolboxes. The simulated results are presented to demonstrate the capability of the proposed controller as a voltage and frequency regulator, harmonic eliminator, load balancer, and neutral current compensator for different electrical (varying consumer loads) and mechanical (varying wind speed) dynamic conditions in an autonomous wind energy conversion system.     

风力发电系统的配置

随着科学技术的发展,新能源得到越来越广泛的应用。下面简要介绍一下为解决边远地区用电问题而设计的3种风力发电系统的配置情况。1 系统配置(1)风蓄互补系统风蓄互补系统就是利用风力发电机、蓄电池对系统进行供(蓄)电,从而满足用户的用电要求。其基本原理是：通过风力发电机将自然风能转换成电能,经系统控制,在输出端输出220 V,50 Hz的交流电;若风力发电超出了用电要求(电能过剩),蓄电池则可以将多余的电能储存起来,在风况不好时再对用户供电,从而达到几个无风日连续供电的目的。该系统的特点是投资少,见效快。但在个别风况不…     

Propagation and Elimination of Torque Ripple in a Wind Energy Conversion System

The 2P and 4P harmonics of the torque supplied by a two blade vertical axis wind turbine propagates in the drive train of the wind turbine and deteriorates the quality of the electric power transmitted to the network. This paper shows how the torque ripple propagates and how it can be eliminated by electrical instead of mechanical means. This elimination is obtained by using a converter-fed synchronous generator and by adopting suitable control strategies.     

Biofuel Based Cogenerative Energy Conversion Systems

The goal of this study is to investigate how co-operation between industry and district heating companies can improve profitability of biofueled cogenerative investments in small to medium-sized applications. Currently advanced biomass gasification and gas turbine combined cycle has been found to be a promising cogenerative conversion technology for the recovery of heat present in biomass fuel. Increased biofuel based cogenerative power production in the future is clearly dependent on the improvement of both performance and investment costs of new high performance technology, and on the nature of policy instruments designed to promote the technology. The use of biofuels for cogeneration on a large scale is focused mainly on forest industry sites, where considerable quantities of biomass are available. While cogeneration provides several environmental benefits by making use of waste heat and waste products, air pollution is a concern any time fossil fuels or biomass are burned.     

A Monte-Carlo Simulation Method for the Economic Assessment of the Contribution of Wind Energy to Power Systems

A method for determining the costeffectiveness of wind energy and the economic limitations of penetration into electrical power systems is presented. It is based on a Monte-Carlo approach which simulates the hour-by-hour operation of the power system. The hourly random variations in wind and load are modeled in addition to the operating constraints inherent in conventional generation. The economic assessment is based on a selected one-year simulation period, Two examples of the application of this method are given.     

Evaluation of Loss of Load Probability and Expected Energy Generation in Multi-area Interconnected Systems with Wind Generating Units

Due to randomness of wind generator＇s availability, power system planners have big concern on EEG （expected energy generation） and system reliability of power system with wind generators. This paper presents a methodology to evaluate the EEG as well as overall LOLP （loss of load probability）, which is an index for system reliability of multi-area interconnected systems with wind generators, as well as conventional fossil fuel based generating units. The proposed model is also capable of tracking the energy export incorporating the multi-state probability model for wind generator which output varies with time and season.     

An Assessment of Wind Turbine Characteristics and Wind Energy Characteristics for Electricity Production

This work is an analysis of wind turbine characteristics and wind energy characteristics of four regions around Elazig, Turkey, namely Maden, Agin Elazig and Keban. Wind speed data and wind direction in measured hourly time-series format is statistically analyzed based on 6 years between 1998 and 2003. The probability density distributions are derived from time-series data and distributional parameters are identified. Two probability density functions are fitted to the measured probability distributions. The wind energy characteristic of all the regions is studied based on the Weibull and the Rayleigh distributions. Using the Weibull probability density function, we estimated the wind energy output and the capacity factor for six different wind turbines between 300 and 2300 kW during the six years. It was found that Maden is the best region, among the regions analyzed, for wind energy characteristic and wind turbine characteristic.     

High-Order Sliding Control for a Wind Energy Conversion System Based on a Permanent Magnet Synchronous Generator

This paper presents the output power control of a wind energy conversion system (WECS) based on a permanent magnet synchronous generator (PMSG). It is assumed that the considered wind module integrates a stand-alone hybrid generation system, jointly with a battery bank, a variable ac load, and other generation subsystems. The operation strategy of the hybrid system determines two possible operation modes for the WECS, depending on the power requirements of the load and the wind availability. The paper deals with the design of a combined high-order sliding mode (HOSM) controller for the power control of the WECS on both operational modes. The main features of the obtained controller are its chattering-free behavior, its finite-time reaching phase, its simplicity, and its robustness with respect to external disturbances and unmodeled dynamics. The performance of the closed-loop system is assessed through representative computer simulations.      

A Review of Direct Driven PMSG for Wind Energy Systems

This paper presents a comprehensive overview study of the DDPMSG （direct driven permanent magnet synchronous generator） for wind energy generation system. Wind turbine controls are provided. The PMSG （permanent magnet synchronous generator） is introduced as construction and model. Configurations of different power converters are presented for use with DDPMSG in wind systems at variable speed operation and maximum power capture. Control techniques for the system are discussed for both machine-side and grid-side in details. Grid integration is provided with focus on how to insure power quality of the system and the performance at disturbances.     

Wind Power [a review of Grid Integration of Wind Energy Conversion Systems (S. Heier; 2006); book review]

This book contains engineering information about the operating principles, design, and application of wind turbines. Grid integration is covered in much less depth and is largely focused upon issues within the medium-voltage collector systems of multi-unit wind farms. Topics covered include power-electronic converter systems, harmonics, filter design, and protection. The book is well suited as a text or reference book for engineering students or researchers. It would also be very useful to wind turbine designers, who need detailed equations and graphs to understand the intricate technical issues related to energy conversion or turbine components.     

Modelling of Chillers for Energy Performance Assessment of HVAC Systems

The reliable assessment of the annual energy demand has become necessary in view of building energy performance certification. Accurate models must be used to simulate the behaviour of HVAC （heating, ventilation and air conditioning） components in real operation, usually characterized by a wide variation of building loads. In this context, this paper deals with the development and validation of an algorithm aimed at the assessment of part load performance of various kinds of controls for vapour compresion based heat pumps and chillers, in particular referring to on-off, inverter-driven and multi-stage vapour compression. The reliability of this algorithm in the calculation of seasonal performances is checked against monitoring of heat pumps and chillers operating under real conditions.     

内蒙古地区风资源评估与风场特征风速的推导

对内蒙古二十四个地区的风能资源进行评估,得到风谱图.首先提出了利用WAsP软件对1998年至2008年期间内蒙古二十四地区的风资源资料中的基础进行分析;然后利用风速威布尔分布函数和风力发电机组输出功率的威布尔的概率密度函数,求两个函数的极值,推导出切入风速和额定风速的公式.最后以内蒙古六个地区为例,计算不同风资源条件下的切入风速和额定风速.     

A New Control Strategy for Modeling Wind Energy Systems Using Fuzzy Cognitive Maps

Wind energy is currently a fast-growing interdisciplinary field that encompasses many different branches of engineering and science. Modeling and controlling wind energy systems are difficult and challenging problems. The basic structure of wind turbines and some wind control system methods are briefly reviewed. The need for using advanced theories from fuzzy and intelligent systems in studying wind energy systems is identified and justified. FCMs （fuzzy cognitive maps） are used to model wind energy systems. Simulation studies are performed and obtained results are discussed. A new mathematical approach has been proposed to model dynamical complex systems, the DYFUKN （dynamic fuzzy knowledge networks）. Many open problems in the areas of modeling and controlling wind energy systems are outlined.     

大功率风力发电机机舱能量节能调节系统设计

首先对风力发电机内部元件的发热状态以及特性进行分析,并介绍了目前风力发电机对于机舱内部温度控制的主要措施以及因为温度控制问题出现的事故。提出一种通过两套循环系统对风力发电机内部温度进行调节的系统,并对其原理和工作方式进行了具体论述,通过和传统温度控制措施的比较,得到本系统在保证温度控制的同时,体现其优越的节能特性。系统节能环保,又有较大的发展前景。