Wind Engineering

In the 1970s, the Netherlands and Denmark both initiated policies to stimulate the development of wind energy. However, the results of these policies are very different. In Denmark, a flourishing wind industry exists nowadays, whereas in the Netherlands only one wind turbine producer remains. Furthermore, the total wind turbine capacity installed in Denmark by 2001 (2,340 MW) was five times greater than in the Netherlands. This paper investigates the differences between the wind energy policies in the Netherlands and Denmark, in particular the learning processes: Do the different learning processes explain the difference in success between the wind energy policies?

The main conclusions are that, in the Netherlands ‘learning-by-searching’ (or R&D) was stimulated far more than in Denmark, whereas in Denmark ‘learning-by-using’ and ‘learning-by-interacting’ were far more important than in the Netherlands. The strong emphasis on learning-by-searching in the Netherlands resulted in a large amount of scientific research and a good international position of the Dutch wind energy researchers. However, the results of this research were little used by the Dutch wind turbine producers.

In Denmark, the domestic market was larger and better organised than in the Netherlands, because at an early stage in Denmark, subsidies for wind turbine purchasers were available. Many contacts existed between the turbine owners, the turbine producers and the wind energy research institute Risø. Due to these contacts, much information was exchanged, which enabled the wind turbine producers to improve their products. Furthermore, because of these good contacts, the reputation of wind energy within Danish society was better than in the Netherlands, which resulted in less difficulty regarding turbine siting. These differences are important reasons for the difference in success between the Dutch and the Danish wind energy policies.

A new process of combining existing wind modelling software has been presented, which is competitive with existing processes of wind modelling in terms of accuracy and efficiency. When compared to real wind speed data, the final rms error in the prediction of average wind speed was around 8%. Further, a model for developing a cost-of-energy atlas is also presented, based on customized GIS tools. Both of these methods can be used with additional land data to quickly identify key sites for wind power development and to ensure rational placement of wind monitoring towers. Indeed, the cost of assessing the wind potential of a large area of land may be less than the cost of one misplaced wind monitoring tower.

This paper illustrates the benefits of using remote sensing methodology as an intermediate step to assess offshore and coastal wind resources. Results are based on an ongoing research to understand wind patterns in the St-Lawrence Gulf. This area combines two advantages for wind power development in Canada: a) very good wind, b) high potential of the large scale integration of wind power with the hydro-wind concept. Advantages and drawbacks of satellite techniques in such a complex environment are reviewed. Our approach of satellite data selection for dominant wind conditions reduces the weakness of Synthetic Aperture Radar (SAR) satellite temporal resolution. Wind fields are extracted from sixteen scenes provided by RADARSAT-1. Results are compared with two main sources: in situ measurements and QuickSCAT scatterometer computations. Among interesting findings, it appears that a relative small sample of scenes can already indicates the best wind sites to be investigated for further analysis. The proposed approach to obtain a global wind map of the gulf and the advantages of such high-resolution wind maps to wind resource assessment are discussed.

This paper reports the results of technical and economic feasibility studies of floating offshore wind farms under typical environmental conditions in Japanese Waters. Outline designs are considered, with economic assessments. Both horizontal and vertical axis wind turbines are considered, although it is realised that horizontal axis machines now dominate.

Until recently it has been accepted that induction generator based wind turbines are disconnected from the power system in the event of a network disturbance. However, the increasing trend of connecting high penetrations of wind farms to transmission networks has resulted in the transmission system operators revising their grid codes for the connection of large MW capacity wind farms. These documents now require wind turbines to remain connected for a specified voltage disturbance on the network. Much of the wind generation plant being developed will use either fixed speed induction generator (FSIG) or doubly fed induction generator (DFIG) based wind turbines. The ability of induction generator based wind turbines to remain connected through power system disturbances is discussed. A control loop for a ‘fast pitching’ blade angle control strategy to provide a power system fault ride-through capability for induction generator based wind turbines is also described. A case study of a FSIG wind turbine with the ‘fast pitching’ initiating logic and control scheme is investigated.

The paper presents an overall control method for variable speed pitch controlled wind turbines with doubly-fed induction generators (DFIG). Emphasis is on control strategies and algorithms applied at each hierarchical control level of the wind turbine. The objectives of the control system are: 1) to control the power drawn from the wind turbine in order to track the wind turbine maximum power operation point, 2) to limit the power in case of large wind speeds, and 3) to control the reactive power interchanged between the wind turbine generator and the grid. The present control method is designed for normal continuous operations. The strongest feature of the implemented control method is that it allows the turbine to operate with the optimum power efficiency over a wider range of wind speeds. The model of the variable speed, variable pitch wind turbine with doubly-fed induction generator is implemented in the dynamic power system simulation tool DIgSILENT PowerFactory which allows investigation of the dynamic performance of grid-connected wind turbines within realistic electrical grid models. Simulation results are presented and analysed in different normal operating conditions.

This paper presents a new wind turbine simulator for steady state conditions. In order to provide a test platform for wind turbine drive trains, the authors have developed an experimental system to simulate the static characteristics of real wind turbines. This system consists of a 10 hp induction motor (IM), which drives a synchronous generator and is driven by a 10 kW variable-speed drive inverter, and real time control software. A microcontroller, a PC interfaced to a LAB Windows I/O board, and an IGBT inverter-controlled induction motor are used instead of a real wind turbine to supply shaft torque. A control program written in the C language is developed that obtains wind profiles and, by using turbine characteristics and the rotational speed of the IM, calculates the theoretical shaft torque of a real wind turbine. Based on the comparison of the measured torque with this demand torque, the shaft torque of the IM is regulated accordingly by controlling stator current demand and frequency demand of an inverter. In this way, the relationships between shaft rotating speed, shaft torque of the IM and wind speed are made to conform to the characteristics of a real wind turbine. The drive is controlled using the measured shaft torque directly, instead of estimating it as conventional drives do.

This paper deals with the control of a stand alone power system comprised of a pitch controlled wind turbine and two diesel units. First, a single-input single-output (SISO) self-tuning regulator (STR) is designed for blade-pitch control, with a conventional diesel governor control. Then, a two-input two-output (TITO) STR is used for coordinated pitch and diesel governor controls. Finally a case study is made with a superconducting magnetic energy storage unit (SMES), introduced as a damping device. In this case, a three-input three-output STR controls the wind-diesel-SMES system in a co-ordinated manner. The design of the various control schemes ensures that the system performs well under both wind and load disturbances.

Since energy requirements for desalination processes are large, the energy supply in remote areas is a problem, especially if electricity is required. The status and perspectives of development of wind-powered desalination are reviewed in this paper. Desalination processes suitable for coupling to wind turbines are reverse osmosis (RO), mechanical vapour compression (MVC) and electrodialysis (ED). Wind-powered RO is the most mature technology whereas there are very few pilot plants of wind-driving MVC and ED.

Due to the expected installed capacity of wind power in Germany in combination with the fade out of conventional electricity generation within the next years, the overall German power plant capability can be changed to be cost effective and to meet CO₂-emission targets. A new energy-economical model called WEsER has been developed to investigate the new situation. This optimizes the conventional power plant generation during one year at hourly resolution, so including wind energy characteristics. The main objective year is 2020. Proposed structures and operation timetables for power plants are calculated. Consequently, WEsER results suggest a new structure of electricity generation mix with large amounts of wind energy. The energy generation share of today's “base load” power stations will decrease, while gas and hard coal complete the generation mix with wind. Economic analysis shows that the additional costs of wind energy are a minimum when emission reduction targets are met.

One of the main concerns of grid-integration of large wind farms with variable-speed wind turbines equipped with doubly-fed induction generators controlled by back-to-back converters is a possible risk of mutual interaction between the control systems of the converters. This topic is discussed and illustrated by simulations on a large wind farm model consisting of eighty wind turbines, when subjected to a short-circuit fault. At no mutual interaction, the wind turbines show coherent response at the grid fault. In such a case, large wind farms can be represented by one-machine equivalent, e.g. one wind turbine model with re-scaled power capacity. This simplification can be applied for voltage stability investigations carried out on detailed models of large power systems.