Lab 3 – Simulation on Wind Power Generation - PDF - PDF by murplelake83

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									ELEC5206 SUSTAINABLE ENERGY SYSTEMS                                                                                                                       Semester 2, 2009



                                                                         Lab 3 – Simulation on Wind Power Generation

Aims
Simulation is an important tool and widely applied on power system analysis. There is a number of
commercial software used by utilities, such as PSS/E (Power Technologies, INC. Canada),
PSCAD (Manitoba HVDC Research Centre Inc.Canada), EMTP-RV (TransÉnergie Technologies
Hydro-Québec group), DigSilent PowerFactory (DigSILENT GmbH Germany), and MATLAB
SIMULINK(MathWorks). To cope with increasing penetration of renewable energy in electric
grid, models to simulate wind or solar power generation have been developed in some software,
for example, DigSilent PowerFactory, PSCAD, and MATLAB SIMULINK.

The objective of this laboratory exercise is to study characteristics of wind power by simulating a
wind farm composed of a doubly-fed induction generator (DFIG) and wind turbine using
MATLAB SIMULINK. By the end of the lab, you will be able to use Simulink to build and
analyze a simple power system with wind power generation.

Overview
A significant feature of wind power in contrast to conventional power is fluctuation of output
power due to wind speeds and turbine locations. This fluctuation affects the voltage profile and
system stability. Figure1 shows that output power of a wind turbine as function as turbine speed at
different wind speeds [1]. The curve in red shows the optimum power at different wind speeds. In
Simulink, the DFIG model uses the red curve for the turbine, which means maximum wind power
tracking is imbedded in the DFIG model.

                                                                                       Turbine Power Characteristics (Pitch angle beta = 0 deg)
                                                                         1.6                                                                 16.2 m/s
                 Turbine output power (pu of nominal mechanical power)




                                                                         1.4


                                                                         1.2


                                                                          1                                                                  D


                                                                         0.8
                                                                                                                                  12 m/s
                                                                                                                                             C
                                                                         0.6


                                                                         0.4

                                                                         0.2
                                                                                       B
                                                                               5 m/s
                                                                          0             A

                                                                           0.6         0.7        0.8       0.9         1        1.1      1.2       1.3
                                                                                          Turbine speed (pu of generator synchronous speed)
Figure 1.



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ELEC5206 SUSTAINABLE ENERGY SYSTEMS                                                           Semester 2, 2009


To extract maximum power at different wind speeds, the speed of wind generator is required to be
varied accordingly to the wind speed. The technology of power electronics (rectifiers, IGBT-based
converters) are employed to change the rotor speed and to convert the frequency to that required
by wind speeds or grid requirements. Pitch angle of blades of a wind turbine can be adjusted to
limit the output power during the gust of wind for protection.

To smooth the output variation and provide more control from the side of power system and wind
turbine itself, DFIG technology is applied on large-scale wind generators. A DFIG consists of a
wound rotor induction generator and an AC/DC/AC IGBT-based PWM converter. The block
diagram is shown in Figure 2. The stator winding is connected directly to the 50Hz grid while the
rotor, which is connected to the rotor-side converter by slip rings and brushes, is fed at variable
frequency through the AC/DC/AC converter. The rotor-side and grid-side converters synthesize an
AC voltage from a DC voltage source which is acted by a capacitor. A transformer is to step up
the voltage to a distribution system as the voltage of wind generators are normally between 500 ~
1000 V due to the high cost. The DFIG technology realizes a variable speed wind generator to
allow extracting maximum energy from the wind for low wind speeds by optimizing the turbine
speed, while minimizing mechanical stresses on the turbine during gusts of wind. Therefore DFIG
is widely used in large scale wind farms. Recently the "5M" turbine (power rating), designed and
built by Germany's Repower has just been connected to the German electrical grid [2].

                                                                                            AC 50Hz
                                                                                              Grid


                                                               Stator Power
      Gear Box




                   DFIG
                                                                                           Transformer
                           Slip Ring
                                                                 DC-link

                                                                                          Rotor Power



                                                Rotor-side                    Grid-side
                                                Converter                     Converter


                           Figure 2. Scheme of a DFIG equipped with wind turbine

In this lab, you will focus on DFIG wind generator and investigate the effects of wind speed and
pitch angle on voltage, real power and reactive power of a DFIG wind generator.

Single-line Diagram of Wind Farm
Wind Farm: 3×1.5MVA, PF of 0.9, 575 V, 50Hz, capacitance of DC link 10000μF, VDC=1200V,
Inertia constant of 5.04, number of pairs of poles=3;
Local Load: Yg connected, 575V, P=200kW, 50Hz;
Step-up Transformer: 3×2MVA, 575V/25kV, Δ-Yg connected, 50Hz;




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ELEC5206 SUSTAINABLE ENERGY SYSTEMS                                                          Semester 2, 2009


Transmission Line: 50Hz, 10km, the positive and zero sequence impedance are:
R1=0.1153Ω/km, R0=0.413Ω/km, L1=1.05×10-3H/km, L0=3.32×10-3H/km, C1=11.33×10-9F/km,
C0=5.01×10-9F/km;
Grid: 25kV, 50Hz, 1500MVA, X0/X1=3.

                                     25kV                                 Tx       575 V

                                                       10km Line

                        Equivalent                                                        Wind Farm
                         System                                                           3*1.5MVA
                Grid    1500 MVA                                         6*2MVA
                         X0/X1=3
                                                                                  200kW
                                                                                   Load



                                 Figure 3. Single-line diagram of the wind farm

Software
MATLAB SIMULINK, the toolbox of SimPowerSystems, The MathWorks. Licensed by
University of Sydney and available on PCs in the lab522.

Pre-lab Work − Build Wind Farm
Use Matlab Simulink and the toolbox of SimPowerSystems to build a wind generation system
shown in Figure 3 before you start this lab. Following steps help you to start with the software. For
more details please refer to the “Help” in Simulink.
   1) Open Matlab, and type “simulink” in the Command Window to get a window of Simulink
       Library Browser. In the menu of File, click New to create a new model in Simulink.
   2) Under SimPowerSystems\Application Libraries\Distributed Resource Library\Wind
       Generation\, drag the model of DFIG (Phasor Type) into the new file.
   3) Under SimPowerSystems\Elements\, drag the model of Three-Phase Transformer (two
       windings), Three-Phase PI Section Line, Three-Phase Mutual Inductance Z1-Z0, and
       Three-Phase Series RLC load into the new file.
   4) Under SimPowerSystems\Electrical Sources\ ,drag the model of Three-Phase
       Programmable Voltage Source into the new file.
   5) Use the model of Three-Phase V-I Measurement located in
       \SimPowerSystems\Measurements\ to measure the voltage and current at the bus of 575V
       and 25kV.
   6) Use the model of Bus Selector located in \Simulink\Signal Routing\ to output parameters
       from the Wind Turbine.
   7) Use the model of Wind Turbine Protection provided in [3] and connected with Trip of
       DFIG. Check and set the proper threshold values for each protection factor.
   8) Since the voltage and currents measured at the buses are complex numbers, relevant math
       functions are used to calculate the amplitudes of the voltage and current, real and reactive
       power before output to the scope which is located in \Simulink\Sinks\. Use the Data
       Acquisition Model in [3] to collect and display the outputs.
   9) Connect the entire system based on the connection of the single-line diagram in Figure 3.
   10) Use the model of Goto or From in \Simulink\Signal Routing\ to output or input a variable
       into a block/subsystem i to tidy up the system connection.


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ELEC5206 SUSTAINABLE ENERGY SYSTEMS                                                 Semester 2, 2009


    11) Double click each model and assign the parameters based on the ratings.

Analysis and Simulation Work
                                                                                                 t ≤ 10s
    1) Set 3*1.5MW for the wind turbine, and wind speed as a step function of f (t ) = ⎧
                                                                                           8
                                                                                       ⎨
                                                                                          ⎩16     t 〉10s
         (step function is located in \Simulink\Sources\). Choose the Phasor Simulation in Powergui
         and set the simulation time as 40s. Simulate the voltage, current, real and reactive power at
         the bus of 575V, wind speed, turbine speed, and pitch angle. Analyse the waveform of each
         variable and comment on the changes when the wind speed changes. You should at least
         cover the questions below and go beyond of them.
                  How do the changes of real power relate to the wind speed?
                  At what wind speeds the pitch angle starts to change, and how is it related to the
                  wind speed and real power?
                  How does the speed of generator change with respect to wind speeds and how are
                  the changes related to the real and reactive power respectively?
                  Is the output voltage a constant or changing with the wind speed? Why?

    2) Set the wind speed as a random function (\Simulink\Sources\) with the range of (6~16 m/s)
       between (0~5minutes), investigate all the variables for the bus of 575V and analyze the
       simulation results. Note the fluctuations of the wind power.


Assessment and Report
The lab takes 3% of the UoS and is assessed by a group report. You report for this experiment
should cover:
      pre-lab work;
      Electronic copy of Simulink file (sent to ruihong@ee.usyd.edu.au);
      Complete simulation diagram, copied from Simulink;
      Simulation results;
      Analysis and comments on simulation results based on the corresponding theories.

Please hand in your report to Ruihong at Room 522A/J03. The report is due on 2 Oct (Fri) at 5pm
latest.

Contact for Help
Assistances are provided on 14 Sep. (Monday) between 11-1pm during the experiment. You also
can get the help by emailing Rui at ruihong@ee.usyd.edu.au or Tom at tom.ki@ee.usyd.edu.au.

Reference
[1] Matlab Simulink toolbox of the \SimPowerSystems\Distributed Resources Library\Wind
Generation\, the Help file of the model of DFIG (phasor type).
[2]http://www.wind-energy-
market.com/index.php?id=18&sb_manageorders%5Buid%5D=208&sb_manageorders%5Baction
%5D=showSingle&sb_manageorders%5Bclass%5D=bigplant&cHash=d965f932a0
[3]Web site of http://www.ee.usyd.edu.au/~ruihong/ (Click ELEC5206-Lab3-Simulink Models).




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