ELEC5206 SUSTAINABLE ENERGY SYSTEMS
Semester 2, 2011
Lab 4 – Integration Wind Power to Electric Grid
Aims
In the lab3 you have built a wind farm connected with an infinite bus, and investigated the
fluctuation of wind power in the steady state. In this experiment, based on the system model built
before, you are to investigate the stability of the system with different disturbances, such as
temporary loss of source voltage, changes of the load, and short circuit faults, and furthermore to
appreciated the control flexibilities of DFIG technologies.
Overview
Wind power has different impacts on power system stability compared with the conventional
power on the aspects below.
 Power flows are considerably different in the presence of high amount of wind power due
to the locations and distributions of wind source.
 Wind generators are usually based on different generator technologies than conventional
synchronous generators.
 Wind generators are usually connected to lower voltage levels, such as distribution
system (20kv, 10kv).
 Wind power is fluctuating due to the weather conditions and local effects.
The impacts are becoming more significant as the wind power penetration to a grid is increasing.
Therefore the following requirements should be met when wind turbines are integrated to the grid.
 Frequency and active power control: Peak output from large wind farms, including
offshore wind farms, may perturb the power system.
 Short circuit power level and voltage variation: according to the short circuit ratings of a
system, the wind turbine connected to the system should not bring the voltage outside the
required limit.
 Reactive power control: Most of large wind generators are induction machines and
consume reactive power, which causes voltage drop and power loss. DFIG with
converters can generate or consume reactive power to control the voltage and power
factor.
 Voltage Flicker: Voltage variation caused by fluctuating wind power generation may
affect voltage quality. DFIG technology can control the output voltage within a limit at
different wind speeds to avoid a flicker.
 System Stability: When faults occur in the system, the voltage drops to low or zero level
for a short period before it restores. In the situation small wind turbines are normally
directly disconnected from the grid. However for large wind farms, wind turbines are
required to have the ability of “ride-through” such disturbances. Various control methods
may be designed to cope with such transients to maintain the system stability.
Overall large wind generators are equipped with various control schemes to be able to meet the
requirements when integrated to the grid. Currently large wind generators using DFIG
technologies can control active and reactive power to maintain the frequency (or speed) and
voltage. They also have low voltage ride-through ability so that wind power can be remained in
the grid when experiencing voltage disturbances. In this lab, you are to focus on investigating the
system stability when having different voltage disturbances.
School of Electrical and Information Engineering, University of Sydney
Rui Hong Chu
1
ELEC5206 SUSTAINABLE ENERGY SYSTEMS
Semester 2, 2011
Pre-lab Work
The model of DFIG in Simulink use voltage source converters, which are controlled by the voltage
signals generated by the control system, shown in Figure 1. The control system includes two parts,
one is for rotor-side converter and the other is for grid-side converter, and is controlled by the
voltage and currents measured from the grid and rotor, reference voltage and current, and wind
speed.
Open the DFIG model (right-hand click the DFIG model, and choose Look Under Mask) and
study the subsystem. Extract and sketch the control scheme in a block diagram for grid/rotor-side
converter in DFIG. Refer to [1].
Figure 1. Schematic diagram of DFIG and its control system
Simulation Tasks
The single-line diagram of the system and the parameter settings are same as the one in the lab3
except for the changes indicated in one of the three conditions below. Wind speed is set up as a
t  5s
8
. For the following cases, simulate the voltages and currents,
step function of f (t )  
14 t 5s
real and reactive power at the bus of 575V and 25kV, wind turbine speed, voltage of the DC link,
wind speed, and the pitch angle.
1) Earth fault at the coupling bus: a single phase fault (phase A-ground, shown in Figure 2)
occurs at the bus of 25kV and the fault lasts 10 cycles of 50Hz.
2) Load variation: an inductive load (P=10kW, Q=20MVar) is switched into the network (at the
25kV bus, as shown in Figure 2).
School of Electrical and Information Engineering, University of Sydney
Rui Hong Chu
2
ELEC5206 SUSTAINABLE ENERGY SYSTEMS
Semester 2, 2011
3) Grid voltage sag: a. the voltage of the grid is dropped suddenly by 0.2pu at t=10s and the sag
lasts 0.5s. b. the voltage of the grid is dropped suddenly by 0.3pu at t=10s and the sag lasts
0.5s.
Analyse the simulation results and explain how the disturbances in the above three circumstances
affect the system stability and the performance of the wind generator. In which case in the
circumstance of 3) the wind turbine is tripped off, and how? Change the Voltage regulation to Var
regulation for the Control parameters in DFIG model, what happens to the simulation results?
25kV Single-phase
earth fault
Grid
575 V
10km Line
Equivalent
System
1500 MVA
X0/X1=3
Wind Farm
3*1.5MVA
6*2MVA
20MVar
Load
200kW
Load
Figure 2. Single-line diagram of the system
Report and Assessment
This lab will be assessed based on a group report and accounts for 2.5% of the UoS. The hard
copy of a report should be handed in the Room522A.
You are required to write a Group report for this experiment, which should cover:

pre-lab work;

Electronic copy of Simulink file (sent to ruihong@ee.usyd.edu.au);

Complete simulation diagrams, copied from the simulation window;

Simulation results and data process;

Analysis and interpretation on your simulation results based on the corresponding theories.
Reference
[1] Help file of the DFIG Model (Phasor Type) in Simulink SimPowerSystem.
School of Electrical and Information Engineering, University of Sydney
Rui Hong Chu
3