ENGR7762 Renewable Energy Systems Practical 1
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ENGR7762
Renewable Energy Systems
Practical 1: Grid-Connected Wind Turbine
Aim:
The aim of this practical is to evaluate basic operating characteristics of a Doubly-fed- induction-generator using the standard MATLAB/Simulink blocks given in SymPowerSystems.
Objectives:
Familiarise with the block diagrams of MATLAB/Simulink.
Develop a simple model of a wind power plant directly connected to a load and grid. Run simulations and familiarise with MATLAB Workspace and graph plotting .
Background:
In contrast to a conventional power generation, wind power is intermittent type, thus the output power of a wind generator cannot be controlled on demand. In other words, wind power is not dispatchable. The fluctuating output power of a wind generator affects the voltage profile, losses, reliability and stability of the system. The output power of a wind turbine depends on wind speed which is stochastic in nature. For a given wind speed, the turbine efficiency or performance coefficient (Cp) depends on the turbine speed and hence tip-speed ratio (入), and blade pitch angle (F). The turbine power (Pm) can be expressed as:
Pm = pAvw(3)Cp (入,F)
Where, p is the air density, A is the blade sweep area and vw is the wind speed.
In this exercise, a doubly-fed-induction-generator (DFIG) will be studied. To extract the maximum power at different wind speeds, the speed of the wind turbine and hence the generator is required to vary according to the wind speeds. This is done by employing partial size back-to-back power electronic converters (ac-dc-ac). The converters are connected to a common dc capacitor. The rotor side and grid side converters synthesize an ac voltage from a dc voltage source (represented by the dc capacitor). The speed control range of the DFIG depends on the size of the converters used. Usually it is about 30% of the rated power of the generator. Blade pitch angle of the wind turbine is also adjusted to limit the output power (at the rated value) during high wind speeds for protection.
Description:
Fig. 1 illustrates the single-line diagram of the wind power plant and the local load considered for this practical.
Fig. 1 Single-line diagram of the wind power plant and the local load.
Fig.2 Block diagram model of the wind power plant and local load in Simulink.
Instructions: Fig. 2 illustrates the corresponding Simulink model block diagram and the procedure for
developing the block diagram is given as follows:
1. Open MATLAB from “Start” menu.
2. Type “slLibraryBrowser” in the Command Window to get the window of the Simulink library.
3. Click “” icon in the tool bar and select “Blank Model” to get a new model.
4. The DFIG block is located in Simscape → Electrical→ Specialized Power Systems→ Electrical Machines→ Wind Turbine Doubly-Fed Induction Generator (Phasor type).
• Drag & drop the model on to the new file or you can right click on the DFIG block and select the “Add block to model” .
• Save the file.
1. Type “Powergui” in the Simulink library search space. Drag & drop the “Powergui” block in to your model.
2. Search for the following blocks and drag & drop them into your Simulink file.
• Three-phase source, constant, step, scope, clock, Three-Phase series RLC load, Bus creator, Bus selector, To workspace block (yout).
3. Connect all the elements as in Fig.2.
4. Right click the “Bus creator” → Block parameter → Set no. of inputs to “7” .
5. Right click on the “Bus selector” → Block parameter → Select P(pu), Q(pu), pitch angle, Tm, wr → Click “OK” .
6. Double click on the “Powergui” block → Select “Solver” → Select the simulation type as “Phasor” and Frequency as “60Hz” → Click “OK” .
7. Double click on the “Three-phase Source” and enter the following parameters:
• Phase-to-phase rms voltage = 575 V, Frequency= 60Hz, Phase angle = 0
• Tick the “Specify short-circuit level parameters” , 3-phase short circuit level = 100e6 VA, Base voltage (Vrms ph-ph) = 575, X/R ratio = 7
8. Double click on the “Three-phase load” block and enter the following parameters :
• In the “Parameters” tab → Nominal phase-to-phase voltage = 575 V, configuration = Y (grounded), frequency = 60 Hz, active power = 100e3 W, Inductive and capacitive reactive power = 0
• In the “Load flow” tab → load type “Constant Z”
9. Double click on the “Constant” block connected to the “Trip” in the wind turbine model → set the constant to “0”
10. Double click on the “Step” block connected to the “Wind” in the wind turbine model and set the following parameters:
• Step time - 5, Initial value - 8, Final value - 10
11. Double click on the scope and click the “View” on the tool bar of the scope and then click the “Configuration Properties” → Select the “Logging” tab → untick the box for “Limit data points to last” → Click “OK” . Do this change on all the scopes.
12. Double click on the “To Workspace” and click the “Save format” and then select the
“Array” .
13. Double click on the ‘Wind Turbine’ model and enter the following parameters:
• Select the “Generator” option → Nominal power, line-to-line voltage, frequency = [1.5e6/0.9 575 60], Stator = [0.00706 0. 171], rotor = [ 0.005 0. 156], Magnetizing inductance = 2.9, Inertia constant, friction factor, and pairs of poles = [5.04 0.01 3], Initial conditions = [0.2 0 0 0 0 0]
• Select the “Turbine” option → Nominal wind turbine mechanical output power = 1.5e6, Tracking characteristic speeds = [0.7 0.71 1.2 1.21], Power at point C - 0.73, Wind speed at point C = 12, Pitch angle controller gain = 500, Maximum pitch angle = 45, Maximum rate of change of pitch angle = 2
• Click on the “Display wind turbine characteristics” and obtain the wind turbine characteristics.
• Save the figure.
14. Set the “Simulation Stop Time” in the tool bar to “60” as follows:
15. Run the simulation by clicking on the “Run” icon in the tool bar.
16. Double click on all the scopes and observe the parameter variations. Click the “Auto scale” icon on the scope toolbar to view the full simulation.
Workspace The MATLAB workspace consists of the variables you create and store in memory during
a MATLAB session. You add variables to the workspace by using functions, running MATLAB code, and loading saved workspaces.
The Workspace browser displays the variables in your workspace. From the Workspace browser, you can select variables to view, modify, or plot.
To open the Workspace browser if it is not currently visible, do either of the following:
• Type workspace at the Command Window prompt.
• On the “Home” tab → click “Layout” . Then, under “Show” , select “Workspace” .
The variables you selected from the DFIG in the previous section (P(pu), Q(pu), pitch angle, Tm, wr) are saved in the “yout” matrix.
Fig. 3 Results of the MATLAB Workspace after running the simulation
Plotting Data MATLAB has an excellent set of graphic tools. Plotting a given data set or the results of
computation is possible with very few commands. Since, all your data related to the simulation is saved in the matrix “yout” in the Workspace, simply follow the following steps to plot different graphs.
17. Type the following command in the command window and press “Enter”
• plot(yout( :,1),yout(:, 2))
The x-axis of the graph denotes the time variable while the y-axis represents the second output coming from the wind generator model.
18. In order to add labels to the x-axis and y-axis and a title, select “Insert” in the graph and select the appropriate labels and title. Then type the label names and the title as illustrated in Fig. 4.
19. Similarly, plot the following outputs from the wind generator in separate figures and save all the figure files. Submit the graphs in a report.
• Time vs Active power, Time vs Reactive power, Time vs Wind speed, Time vs Pitch angle, Time vs Rotor speed, Time vs Mechanical Torque
Fig. 4 Adding axes labels and titles to a graph
In your Report: 1. Include all plots of step 22 with critical analysis and discussions.
2. Describe the power characteristic of a DFIG based wind generating system (i.e. turbine power versus turbine speed for various values of wind speed).
3. What are the main differences between Type-3 and Type-4 wind generating systems?
For the analysis of power systems or electrical machine system, different values are required, thus, per unit system provides the value for voltage, current, power, impendence and admittance. The Per-Unit System also makes the calculation easier as all the values are taken in the same unit. Calculations are simplified because quantities expressed as per-unit do not change when they are referred from one side of a transformer to the other. This can be a pronounced advantage in power system analysis where large numbers of transformers may be encountered. The per-unit system is mainly used in the circuit where variation in voltage occurs.
2022-09-14
Grid-Connected Wind Turbine