Simulation takes 137 seconds. Input wind data is interpolated by the system with 0.05 second sample time. Totally, simulation includes 20 x 137 = 2740 steps.
Small sample time enables system to be stable and captured power to be kept around the rated value. Note from Figure 5.10 that, output power fluctuations can be kept in 200 kW tolerances.
All graphical results of the simulation are shown below.
Figure 5.8 Wind speed values filtered by yaw control block
Figure 5.9 Aerodynamic power in the wind
Figure 5.10 Captured wind power by the turbine (Input power to generator)
Figure 5.11 Angular speed variation of the turbine in respect of each wind speed change (Change of input torque)
Figure 5.12 Angular shaft speed of the turbine
Figure 5.13 Rotational speed of turbine shaft before gearbox
Figure 5.14 Rotational speed of turbine shaft after gearbox (Rotational speed of generator rotor)
Figure 5.15 Tip speed ratio
Figure 5.16 Blade pitch angle (a)
Figure 5.17 Power coefficient (Cp)
Figure 5.18 Tip speed ratio vs. power coefficient
Figure 5.19 Turbine wind speed – power characteristics
Figure 5.20 Turbine efficiency vs. wind speed
In Table 5.1, variations of all parameters of the wind turbine can be observed corresponding to each available wind speed value. Note that, until wind speed (V) reaches the rated value, pitch angle (a) kept at zero by the system, and after the rated wind speed occurred, pitch angle is started to increase in order to allow keeping the output power (Pcap) around rated value At the same time, the available aerodynamic wind power (Pw) is still increasing.
Table 5.1 Modelled Wind Turbine Simulation Results V
(m/s)
Pw
(kW)
? a
(degrees)
Cp Pcap
(kW)
5 330 15.7 0 0.21 51
6 570 13.4 0 0.36 165
7 904 11.9 0 0.42 323
8 1,345 10.8 0 0.44 514
9 1,922 10 0 0.44 753
10 2,632 9.4 0 0.43 1,031
11 3,505 9 0 0.42 1,360
12 4,551 8.6 0 0.41 1,732
13 5,788 8.3 2 0.35 1,925
14 7,225 7.1 2.5 0.30 2,020
15 8,890 6.7 4.5 0.24 1,999
16 10,790 6.35 6 0.21 2,052
17 12,938 5.9 7 0.16 1,869
18 18,466 5.6 8.5 0.14 1,847
CHAPTER SIX
CONCLUSIONS
Wind power is a deceptively simple technology. Behind the tall, slender towers and gently turning blades lie a complex interplay of lightweight materials, aerodynamic design and computerized electronic control.
Although a number of variations continue to be explored, the most common configuration has become the horizontal three bladed turbine with its rotor positioned upwind on the windy side of the tower. With this broad envelope, continuing improvements are being made in the ability of the machines to capture as much energy as possible from the wind. These include more powerful rotors, larger blades, improved power electronics, better use of composite materials and taller towers.
The most dramatic improvement has been in the increasing size and performance of wind turbines. From machines of just 25 kW twenty years ago, the typical size being sold today is up to 2500 kW.
Today’s wind turbines include properties of modern technology. They are modular and very quick to install and commission.
Advantages of using wind energy conversion systems instead of other energy production systems are;
• Environmental protection (No CO2 emission)
• Low-cost. Wind can be competitive with nuclear, coal and gas
• Diversity and security of supply
• Rapid deployment. Modular and quick to install
• Fuel is abundant, free and inexhaustible
• Costs are predictable and not influenced by fuel price fluctuations
• Land- friendly. Agricultural / industrial activity can continue around it
Power control of the studied horizontal axis, variable speed wind turbine is made by pitch angle adjustment. This seems as the most efficient method to supply 3-phase utility grids. As the number of wind speed samples increases, the pitch control mechanism works more efficiently, in other words; the oscillations around rated power line can be minimized above rated wind speeds.
Moment of inertia, rotor diameter and gear ratio are three critical parameters for a variable speed wind turbine and must be selected carefully by manufacturers while designation.
Moment of inertia is the rotational mass of the turbine rotating parts. The constructing material of blades and other rotating masses should be selected optimum to verify the minimum cut- in wind speed. This means minimum starting torque and maximum usage of the wind power.
Rotor diameter is directly specifies the swept area and so captured power from the wind. It should be selected carefully to ensure reaching rated power output level and allowing minimum cut- in wind speed. For this purpose, long time wind speed measurements should be made and then it will be possible to investigate the optimum wind speed interval to allow maximum overall energy capturing.
Gear ratio is the adjustment location of induction machine generator region. For example, in the studied system, 20-28.5 rpm operating interval of low-speed shaft is modified into 760-1083 rpm region for a 750 rpm synchronous speed asynchronous machine with the gear ratio of 38.
Although tip speed ratio values seem acceptable in both raising and falling regions of ?–Cp curve, allowing tip speed ratio to exceed 10 causes the over-speed of generator rotor, resulting in the physical damage of machinery parts.
Figure 6.1 ?–Cp curve indicating operating regions of the generator
6.1 FUTURE PROSPECTS
In the future, even larger turbines than today’s 2500 kW will be produced to service the new offshore market. Machines in a range from 3000 kW up to 5000 kW are currently under development. In 2002, the German company Enercon is scheduled to erect the first prototype of its 4500 kW turbine with a rotor diameter of 112 meters. (EWEA, European Wind Energy Association, 2002, p.13)
European Wind Energy Association (EWEA) which is the international voice of the wind industry located in the center of Europe has launched an industrial blueprint including the targets to be reached by 2020.
The main objectives of this study are;
• Supplying 12 % of global electricity demand, assuming that global demand doubles by then
• Creation of 1475 million recruitments
• Cumulative CO2 savings of 11,768 million tones
• 1,261,000 MW wind energy capacity installed generating 3093 TWh, equivalent to the current electricity use of all Europe
This study demonstrates that there are no technical, economic or resource limitations to achieve this goal, but the political and policy changes are required in order for the wind industry to reach its full potential.
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APPENDICES
Get wind data (V)
- FLOWCHART OF THE SIMULATED SYSTEM -