- Damping of Blade-shaft Torsional Oscillations of Wind Turbine Generator System
S. M. Muyeen, Mohd Hasan Ali, Rion Takahashi, Toshiaki Murata and Junji Tamura.
Electric Power Components & Systems, Vol. 36, No. 2, Feb. 2008, pp. 195-211.
In this article, the blade and shaft torsional oscillations of wind turbine generator system (WTGS) when a network disturbance occurs in the power system are analyzed. Several reports are available in the literature, where the damping of shaft torsional oscillations of steam turbine generator system is discussed. Though a huge number of wind generators are going to be connected with the existing network, the damping of blade-shaft torsional oscillations of WTGS has so far not been reported. In this work, for the damping of blade-shaft torsional oscillations of WTGS, the voltage source converter (VSC) based three-level STATCOM is proposed. The six-mass drive train model of WTGS is used for the sake of precise analysis. Moreover, the damping of blade-shaft torsional oscillations of WTGS by using pitch controller is analyzed also, since a pitch controller is attached with most of the recent wind turbines. Both symmetrical and unsymmetrical faults are considered as the network disturbances. Simulation results clearly show that the pitch controller can somewhat, and the STATCOM can significantly, decrease the blade and shaft torsional oscillations of WTGS, where the simulations have been done by PSCAD/EMTDC.
- Modelling and validation of a squirrel cage induction generator wind turbine during connection to the local grid
G. Quinonez-Varela and A. Cruden.
IET Generation, Transmission and Distribution, Vol. 2, No. 2, Mar. 2008, pp. 301-309.
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).
- On the nonlinear structural analysis of wind turbine blades using reduced degree-of-freedom models
K. Holm-Jurgensen and S. R. K. Nielsen.
Structural Engineering and Mechanics, Vol. 28, No. 1, Jan.10 2008, pp. 107-127.
Wind turbine blades are increasing in magnitude without a proportional increase of stiffness for which reason geometrical and inertial nonlinearities become increasingly important. Often these effects are analysed using a nonlinear truncated expansion in undamped fixed base mode shapes of a blade, modelling geometrical and inertial nonlinear couplings in the fundamental flap and edge direction. The purpose of this article is to examine the applicability of such a reduced-degree-of-freedom model in predicting the nonlinear response and stability of a blade by comparison to a full model based on a nonlinear co-rotating FE formulation. By use of the reduced-degree-of-freedom model it is shown that under strong resonance excitation of the fundamental flap or edge modes, significant energy is transferred to higher modes due to parametric or nonlinear coupling terms, which influence the response and stability conditions. It is demonstrated that the response predicted by such models in some cases becomes instable or chaotic. However, as a consequence of the energy flow the stability is increased and the tendency of chaotic vibrations is reduced as the number of modes are increased. The FE model representing the case of infinitely many included modes, is shown to predict stable and ordered response for all considered parameters. Further, the analysis shows that the reduced-degree-of-freedom model of relatively low order overestimates the response near resonance peaks, which is a consequence of the small number of included modes. The qualitative erratic response and stability prediction of the reduced order models take place at frequencies slightly above normal operation. However, for normal operation of the wind turbine without resonance excitation 4 modes in the reduced-degree-of-freedom model perform acceptable.
- Optimal wind-battery coordination in a power system using evolutionary iteration particle swarm optimisation
T. -Y Lee.
IET Generation, Transmission and Distribution, Vol. 2, No. 2, Mar. 2008, pp. 291-300.
An evolutionary iteration particle swarm optimisation (EIPSO) approach for optimal wind-battery coordination in a power system is proposed. The up-spinning reserve and down-spinning reserve are introduced into the wind-battery coordination problem to improve system security and the wind utilisation factor. The optimal operating schedule for a battery energy storage system (BESS) and thermal unit was reached while minimising the total operating cost. Taiwan Power Company System is used as a numerical example to test the new algorithm. The feasibility of the new algorithm is demonstrated by the numerical example, and the EIPSO solution quality and computation efficiency are compared with those of other algorithms. The results are used to evaluate the effects of the wind turbine generator and BESS on power system operations.
- Practical ways of evaluating wind speed persistence
Energy, Vol. 33, No. 1, Jan. 2008, pp. 65-70.
Wind speed persistence is a measure of the mean wind speed duration over a given period of time at any location. This definition implies that wind speed persistence means a positive serial correlation in time series. The wind speed persistence provides useful information about the general climatological characteristics of the wind persisting at a given location. Therefore, wind speed persistence should be taken into account in many studies such as weather forecast, site selection for wind turbines and synthetic generation of the wind speed data. On the other hand, if wind direction information is considered together with the wind speed then this type of persistence can be used for additional purposes such as forest fires, dispersion of the air pollutants, building ventilation, etc. In this study, three different methods with some modifications of the previous methods have been applied to the wind speed data obtained from the meteorology stations located at the northwest part of Turkey. These methods are based on autocorrelation function, conditional probability and the wind speed duration curves. It has been shown that the proposed methods clearly reflect the persistence properties of the wind speed in the study area.
- Application of PWM rectifier in VSCF wind power system
Ya-Lin Li, Han-Shan Li and Yong-Feng Ren.
Kezaisheng Nengyuan (Renewable Energy Resources), Vol. 25, No. 6, Dec. 2007, pp. 60-64.
In the variable-speed constant-frequency (VSCF) wind power system, the AC excitation power supply should possess excellent input and output performance and bi -direction flowing ability of energy. The back-to-back PWM converter is the optimum scheme of AC excitation power source in which the PWM rectifier is the key technology. This paper analyzes the mathematical model based on the three-phase static coordinate and the two-phase synchronous rotational coordinate according to the topological structure of the main circuit. The principle of the two closed-loop control and the application of the space vector pulse width modulation in the three-phase VSR are also studied. Simulation of the unity power factor rectification and inversion under the environment of Matlab-Simulink were carried out. The results verify that the three-phase VSR can provide sinusoidal input current with unity power factor.
- Dynamic stability simulation of double-fed wind generator connected into power grid
Guang-Xin Yan, Qin Chao, Xin-Gang Liu and Wei Zhou.
Dianwang Jishu / Power System Technology, Vol. 31, No. 24, Dec. 2007, pp. 63-65, 76.
The basic structure of variable speed constant frequency (VSCF) double-fed wind turbine unit is presented and the dynamic mathematical model of VSCF double-fed wind generator unit in d-q coordinate system is established. By use of Matlab/Simulink the simulation modules for VSCF double-fed wind turbine unit are set up and the dynamic stability of double-fed wind generator connected into power grid is simulated. Simulation results show that the established model is correct. The utilization rate of wind energy can be greatly heightened by applying variable speed technology to wind power generation system and power system stability can also be improved. Variable speed double-fed wind turbine unit have function of low voltage ride through (LVRT).
- A Mighty Wind
Plenty, No. 18, Oct.-Nov. 2007, pp. 30-31.
The wind turbines that engineer Bil Becker installed on top of a Chicago apartment building last year probably don't resemble the structures that pop into your head when you think 'windmill.' Instead of propellers mounted on soaring poles, these turbines are made primarily with curved, galvanized steel shaped like the double helix of DNA. This special design means that they can generate renewable electricity in the densely-built urban environment, unlike their counterparts found twirling in the boonies. Becker's Chicago company, Aerotecture International, is just one of a growing number that is developing rooftop wind turbine technology. Unlike the towering, free-standing commercial variety, these vertical-axis wind turbines extend from buildings, capturing winds blowing from any direction. Some can generate electricity in conditions running the gamut from 8-mile-perhour breezes to 100-mile-per-hour gusts - a range nearly three times that of conventional.
- Optimal hydrogen storage sizing for wind power plants in day ahead electricity market
C. Brunetto and G. Tina.
IET Renewable Power Generation, Vol. 1, No. 4, Dec. 2007, pp. 220-226.
Wind energy generation does not often match energy market prices, which are tightly related to consumer demand. The coupling of wind energy conversion system with a storage medium improves the programmability of such generation plants, allowing suppliers to bid both in the energy and services market, and providing suitable profit margins for investors. Today, the `renewable hydrogen'system, where hydrogen is produced by electrolysis, as an energy storage medium represents a way to fully exploit the economic opportunity of energy markets. Optimal sizing of a wind energy storage plant based on hydrogen technology has been analysed. Algorithms are applied in different simulations, varying some parameters such as efficiency and power rating of the plant's sub-systems, that is, electrolyser, fuel cell and storage tank (H2) with regard to their actual and forecasted cost. As a case study, a big wind farm in Sicily and the day ahead market prices in the Italian power exchange have been considered. The results show the incidence of the different components over the total system cost, fixing the possible values that make such a plant feasible considering the net present value.
- Ride-through control strategy of AC excited wind-power generator for grid short-circuit fault
Jun Yao, Yong Liao and Jian-Ping Tang.
Zhongguo Dianji Gongcheng Xuebao (Proceedings of the Chinese Society of Electrical Engineering), Vol. 27, No. 30, 25 Oct. 2007, pp. 64-71.
A new excitation control strategy is proposed for the rotor side converter in an AC excited wind-power generator to allow the system to ride through the grid short-circuit fault. The transient physical course of the AC excited generator (ACEG) and the reason for the rotor over current during the fault are analyzed. In order to avoid the over current in the rotor during the fault, the rotor current AC components produced by the stator currents at 50Hz have been successfully restrained and the stator resistance is also used to demagnetize the machine. A commercial 2 MW AC excited wind-power generation simulation system is set up. Compared with the traditional 'crowbar protection'strategy, the proposed control strategy is validated by the simulation results under the grid symmetrical and unsymmetrical fault conditions. The rotor excitation converter has been successfully protected during the grid fault and it improves the fault ride-through ability of the AC excited wind-power generation system.