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Homework answers / question archive / EEET 3050 - Renewable Energy Systems Practical 2 – DFIG Feeding Power to a Grid through a Transformer and a Line Aim: The aim of this practical is to evaluate the characteristics of a DFIG based wind power plant connected to the grid through a transformer and a distribution line using standard MATLAB/SIMULINK blocks given in Simscape

EEET 3050 - Renewable Energy Systems

Practical 2 – DFIG Feeding Power to a Grid through a Transformer and a Line

Aim: The aim of this practical is to evaluate the characteristics of a DFIG based wind power plant connected to the grid through a transformer and a distribution line using standard MATLAB/SIMULINK blocks given in Simscape.

Objectives: Familiarise with modification/extension of MATLAB Simulink models

Develop the model of a realistic wind power plant feeding power to a grid

Investigate the system responses to change in wind speed

Background: Background and theory related to this practical have been covered in Practical - 1. In this practical, you will be modifying the Simulink model developed in Practical - 1 to represent a more realistic model of a wind generating system.

Description:

Fig.1 illustrates the single line diagram of the wind power plant and the utility grid considered for this practical. Fig. 2 illustrates the corresponding Simulink model block diagram. The procedure for developing the block diagram (or modifying the diagram of practical 1) is given in the following.

Fig.1 Single line diagram of the wind power plant and the grid

Fig.2 Model block diagram in Simulink

1. Open MATLAB from ‘Start’ menu.

2. Select ‘Open’ → Open the Simulink model saved from Practical 01.

3. Select ‘File’ → Save as → Save the Simulink file with a different name.

4. Click ‘Simulink Library’ icon in the tool bar to get the window of the Simulink library.

5. Search for the following blocks and drag & drop them into your Simulink file.

• Three-phase PI section line, Three-phase transformer (two winding), Three-phase V-I measurement, scope, Abs, Step, Sum

6. Delete only the lines connecting the ‘Three-Phase Source’ and the ‘Three-Phase Series RLC load’. Insert the new elements and connect all as in Fig.2. Right click on Three-phase V-I measurement block and select ‘flip’ to get required configuration.

7. Choose the solver: Click on the ‘Variable step auto’ (bottom right corner) → Settings → Solver → ode 45 (Dormand-Prince).

8. Double click on the ‘Three-phase Source’ and enter the following parameters:

• Phase-to-phase rms voltage -11 kV, Frequency - 60Hz, Phase angle - 0, 3-phase short circuit level - 100 MVA, X/R ratio – 7, Base voltage – 11 kV.

9. Double click on the ‘Three-phase PI section line’ and enter the following parameters:

• Line length - 10 km

Resistance( Ohm/km)

Inductance (mH/km)

Capacitance (nF/km)

Positive seq.

0.01273

0.9337

12.74

Zero seq.

0.3864

4.1264

7.751

10. Double click on the ‘ Transformer’ and enter the following parameters:

• In the ‘Configuration’ tab → winding 1 ‘Yg’ and winding 2 ‘Delta (D1) ‘

• In the ‘Parameters’ tab → Nominal power - 2.0 MVA, frequency - 60 Hz, Winding 1 parameters - [11e3, 0.002, 0.08], Winding 2 parameters - [575, 0.002, 0.08], Magnetizing resistance - 500, Magnetizing inductance - 500

11. 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 - 100 kW, Inductive and capacitive reactive power - 0

• In the ‘Load flow’ tab → load type ‘Constant Z’

12. 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.

13. Remove the ‘Step’ block connected to the ‘Wind’ input of the DFIG model. Connect the ‘Sum’ block and other ‘Step’ blocks as in Fig. 2.

14. Double click on the ‘Sum’ block and in the ‘List of signs’ enter |++++

15. In order to obtain the step variation of wind speed connect four different step blocks to the summation block as illustrated in Fig. 2 and enter the following parameters:

Block

Step time

Initial value

Final value

Step 1

100

8

10

Step 2

200

0

2

Step 3

300

0

2

Step 4

400

0

2

16. Right click the ‘Bus creator’ → Block parameter → Set no. of inputs to ‘7’.

17. Right click on the ‘Bus selector’ → Block parameter → Select P (pu), Q (pu), pitch angle, Tm, wr→ Click ‘OK’. Connect the signals from the ‘ Bus selector’ to the ‘Bus creator’

18. Double click on the scope and click the ‘Parameter’ icon on the tool bar of the scope → Select the ‘Logging’ tab → untick the box for ‘Limit data points to last’ →Click ‘OK’. Do this change on all the scopes.

19. Set the ‘Simulation Stop Time’ in the tool bar to ‘500‘ as follows:

20. Run the simulation by clicking on the ‘Run’ icon in the tool bar.

21. 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.

22. To open the Workspace browser if it is not currently visible, do either of the following:

• Type workspace at the Command Window prompt.

• The variables you selected from the DFIG in the previous section (P (pu), Q (pu), pitch angle, Tm, wr) are saved in the ‘simout’ matrix.

23. Type the following command in the command window and press ‘Enter’:

• plot(out.simout( :,1),out.simout(:, 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.

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. Alternatively, double click on ‘arrow’ of figure toolbar and edit the axis by double clicking on any of the axis. Save the plot or use ‘Copy Figure’ option from Edit menu and paste the figure in the word document.

24. 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

Report:

1. Include all plots of step 24 with critical analysis and discussions.

2. How does the speed of the generator change with wind speed?

3. Plot the voltage and current of the DFIG (at 575-V bus) and describe their variation with the change in wind speed.

4. What is the reason of using the 11kV/575V transformer in the system?

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