Wind Energy Conversion Systems

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Dates and Mechanisms for Assessment Submission and Feedback
COURSEWORK ASSESSMENT SPECIFICATION

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Faculty of Engineering and Environment
KD7011: MSc ELECTRICAL POWER ENGINEERING
EN0711: MEng ELECTRICAL & ELECTRONIC ENGINEERING
Module: Wind Energy Conversion Systems
Assignment Brief:
Wind turbine induction generator for stand-alone applications
Value: 40% of Module
Assignment Tutor: Dr Milutin Jovanovic
1. Requirements
• Write a report (a text of maximum 1000 words, excluding diagrams, contents,
references etc.) to include responses to the tasks from Section 3. You can use
technical publications, books or any other usual University Library resources,
but you must not make verbatim extracts from these. Sources of information
should be acknowledged and appropriately referenced in your report.
• Submit the report via the Blackboard module site no later than 18th Dec 2020.
• Academic Integrity Statement: You must adhere to the University Regulations on
academic conduct. Formal inquiry proceedings will be instigated if there is any
suspicion of plagiarism or any other form of misconduct in your work. Refer to
the University’s Assessment Regulations for Northumbria Awards if you are
unclear as to the meaning of these terms. The latest copy is available on the
University website.
• Failure to submit: The University requires all students to submit assessed
coursework by the deadline stated above. Where the coursework is submitted
without prior approval after the published hand-in deadline, penalties will be
applied as defined in the University Policy on the Late Submission of Work
available at: https://www.northumbria.ac.uk/about-us/university-services/academicregistry/quality-and-teaching-excellence/assessment/guidance-for-students/
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2. Case Study
The main objective of the assignment is to simulate dynamic performance of a
typical fixed-speed autonomous wind-diesel energy conversion system (WECS) for
remote geographical areas isolated from a conventional utility grid. A structural block
diagram (Fig. 1) and details of such a system are presented in the Appendix. The 3-
phase WECS considered consists of a classical wound-rotor diesel synchronous
generator, a wind turbine driving a cage induction generator, a Y-connected
customer load, and a variable secondary load. The power system is initially operated
in steady state supplying the main load only, and an additional load is switched on at
0.3 s time instant by closing the circuit breaker. You are expected to analyse the
system transient response to this step load change by computer simulations and
make the relevant conclusions/observations from the results obtained.
The Wind Turbine block uses a 2-D Lookup Table to compute the turbine
torque output (Tm) as a function of wind speed (w_Wind) and turbine speed (w_Turb)
according to the wind turbine characteristic shown in Fig. 2.
The Secondary Load block is represented by eight sets of 3-phase resistors in
series with GTO thyristor switches, which can be assumed ideal for convenience of
analysis. The nominal power of each set follows a binary progression so that the load
can be varied from 0 to 446.25 kW in 1.75 kW steps.
3. Tasks
(1) How are the voltage and frequency control achieved in the WECS of Fig. 1 at
low (say, 5 m/s or 6 m/s) and high (e.g. 11 m/s) wind speeds? Identify the
respective operating modes of the synchronous machine under these two wind
conditions? Explain your answers.
(8%)
(2) Study the classical d-q theory of 3-phase synchronous generators and 3-phase
induction generators, and write the respective dynamic model equations in a
rotor reference frame defining the meanings of ALL the parameters used.
Ignore iron losses and magnetic saturation.
(14%)
(3) Show a structural diagram and explain the main function(s) of the Discrete
Frequency Regulator block in Fig. 1.
(8%)
(4) Implement the block diagram of Fig. 1 in Matlab/Simulink environment and run
the simulations for 10 s (with a sudden load change occurring at 5.3 s) at a wind
speed of 11 m/s using the ode23tb numerical integration routine. Assume a
linear magnetic circuit of the machines i.e. do not simulate saturation effects.
Present and discuss qualitatively the generated waveforms for the following
performance indicators in your report: (a) voltage [pu]; (b) current [pu] and real
power [kW] of the: consumer load, induction generator and secondary load; (c)
reactive power of the synchronous machine [kVAr]; (d) induction machine speed
[pu], and (e) system line frequency [Hz].
(40%)
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(5) Using the above results and the information provided in Fig. 2, estimate the
power factor of the induction generator in steady-state after connecting the
additional 50 kW load. Compare the numerical (i.e. from your computer
simulations) and analytical (i.e. model predictions using an approximate
equivalent circuit and ignoring magnetising reactance) solutions for the
induction generator electrical power under these operating conditions.
(30%)
4. Appendix: WECS configuration and parameters
Fig. 1: A generic model of a stand-alone diesel-wind generation system
4-pole, 480 V, 300 kVA, 60 Hz, Y-connected, salient-pole, synchronous generator:
Stator resistance [pu] = 0.02;
Reactances [pu]: = 3.2; ‘ = 0.2; ” = 0.15; = 2.8; ” = 0.37; = 0.1
X d X d X d X q X q X l
Open-circuit time constants [s]: Tdo’ = 1.7;Tdo” = 0.08;Tqo” = 0.04
Inertia constant [s] and friction coefficient (factor) [pu]: H = 1 and F = 0
4-pole, 480 V, 275 kVA, 60 Hz, Y-connected, cage induction generator:
Stator resistance = Rotor resistance = 0.02 pu
Stator leakage inductance = Rotor leakage inductance = 0.06 pu
Mutual inductance = 3.5 pu
Inertia constant and friction factor: H = 2 s and F = 0
Consumer Load
Read the model properties
for initialization details
10

w_Wind
w_Turb
Tm
Wind Turbine
A B C
a b c
WT
Pm
Vf _
m A B C
Synchronous Generator
480V 300kVA
Double click to display
Turbine characteristics
Control
A B C
Secondary
Load
(0-446.25 kW)
Scope2
Scope1
A B C
a b c
SL
A B C
a b c
SC

Power
Computation
ABC
PF Correction
Capacitor
70 kvar

A B C
Load a b c
Tm
[w_ASM]
[Vabc_SL]
[Vabc_SC]
[Iabc_SL]
[Freq]
Vf m
Excitation
?
Double click here for info
Control Vabc
Discrete
Frequency Regulator
A B C
a b c
0
0 kW
Frequency (Hz)
Vabc (pu)
Iabc Sec. Load (pu/275 kVA)
ASM speed (pu)
<Rotor speed (wm)>
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3-phase circuit breaker (for connecting an additional 50 kW load)
Transition time [s] = 0.3 (this is the breaker closure instant)
Series resistance = 0.001 Ω
Snubbers resistance = 1 MΩ (with an infinitely high capacitance)
Discrete frequency regulator
Sample time = 200 µs
Regulator gains (proportional and differential): 255 and 30.
Fig. 2: Power curves of the turbine at various wind speeds
Milutin Jovanovic
Dr M. Jovanovic October 2020
500 1000 1500 2000 2500 3000
0
0.2
0.4
0.6
0.8
1
1.2

Wind turbine characteristics
Power (pu/275 kW)
Turbine speed referred to generator side (rpm)