A Hybrid Wind/Solar Energy Converter
SIM UNIVERSITY
SIM UNIVERSITY
SCHOOL OF SCIENCE AND TECHNOLOGY
A HYBRID WIND/SOLAR ENERGY CONVERTER
FINAL REPORT
STUDENT
: QI SHUAI (PI NO. Q0805944)
SUPERVISOR
: PROF. ALI I MASWOOD
PROJECT CODE
: JAN2010/ENG/0016
A project report submitted to SIM University
in partial fulfilment of the requirements for the degree of
Bachelor of Engineering
November 2010
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TABLE OF CONTENTS
i. Abstracts ................................................................................................................................... i
ii. Acknowledgement .................................................................................................................. ii
iii. List of Figure.......................................................................................................................... iii
iv. List of Table ........................................................................................................................... vi
Chapter 1 Investigation of Project Background
1.1 Renewable Energy ............................................................................................................1
1.2 Solar/Wind Energy Converter System ..............................................................................3
1.2.1 Solar Energy Converter System .................................................................................3
1.2.1.1 Solar (PV) Panel ..................................................................................................3
1.2.1.2 Charge Converter ...............................................................................................3
1.2.1.3 Batteries .............................................................................................................3
1.2.1.4 Inverter ..............................................................................................................4
1.2.2 Wind Energy Converter System.................................................................................5
1.2.2.1 Wind Turbine .....................................................................................................5
1.2.2.2 Tower .................................................................................................................6
1.2.3 Performance of Solar/Wind Energy System ..............................................................7
1.3 Hybrid Solar/Wind Energy Converter System ..................................................................8
Chapter 2 Review of Theory and Previous Work
2.1 Wind Turbine Generation .................................................................................................9
2.2 AC-DC Diode Rectifier .......................................................................................................9
2.3 Solar Cell Equivalent Circuit ............................................................................................11
2.4 Maximum Power Point Tracker (MPPT) .........................................................................12
2.5 DC-DC Converter.............................................................................................................13
2.5.1 Non-Isolated Converter Topology ...........................................................................13
2.5.1.1 Boost Converter ...............................................................................................13
2.5.1.2 Buck Converter ................................................................................................15
2.5.1.3 Non Inverting Buck-Boost Converter ...............................................................16
2.6 DC – AC Inverter .............................................................................................................17
Chapter 3 Project Management
3.1 Project Objective ............................................................................................................19
3.2 Overall Objective ............................................................................................................19
3.3 Project Outline................................................................................................................20
3.4 Project Circuit Design Flow Chart ...................................................................................21
3.5 Gantt Chart .....................................................................................................................22
Chapter 4 Design and Simulation
4.1 Design of Solar Controller ...............................................................................................23
4.1.1 Modeling of Photovoltaic Panel ..............................................................................23
4.1.2 Design the Boost MPPT – Open Loop......................................................................25
4.1.3 Design of Boost MPPT – Close Loop ........................................................................27
4.1.4 Closed Loop MPPT Waveform Simulation...............................................................31
4.2 Design of Wind Controller ..............................................................................................35
4.2.1 Design of Buck – Boost Mode Selector Circuit ........................................................35
4.2.2 Design of Buck Converter ........................................................................................36
4.2.3 Design of Boost Converter ......................................................................................38
4.2.4 Wind Converter Simulation with DC Type WTG ......................................................40
4.2.5 Wind Converter Simulation with AC Type WTG ......................................................42
4.3 Design of Charge Controller ...........................................................................................46
4.4 Design of Inverter ...........................................................................................................47
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Chapter 5 Summary. Conclusions and Future Work
5.1 Conclusion ......................................................................................................................52
5.2 Critical Review & Reflections ..........................................................................................52
5.3 Future Recommendation................................................................................................53
Reference ................................................................................................................................. vii
Appendix A Schematics ........................................................................................................... viii
A.1 Solar Controller MPPT Schematics ................................................................................ viii
A.2 Wind Controller Non-Inverter Back-Boost Schematics ................................................. viii
A.3 Charge Controller Schematics ......................................................................................... ix
A.4 Inverter Schematics .......................................................................................................... x
Appendix B Simulation Plot ....................................................................................................... xi
B.1 PV Array ........................................................................................................................... xi
B.2 Closed Loop MPPT at Different Irradiance Level ........................................................... xiv
B.3 Wind Controller with different Voltage Level DC WTG ................................................ xxv
Appendix C Product Specification ....................................................................................... xxxvii
C.1 Solar Panel Specification ........................................................................................... xxxvii
C.2 Wind Turbine Specification ........................................................................................xxviii
C.3 6V Lead Acid battery Specification ...............................................................................xxix
Appendix D PSIM Simulation Software .................................................................................. xxx
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SIM UNIVERSITY
Abstracts
This report proposes an integrated hybrid solar / wind energy converter
constructed using electronics power circuits design in a simulation
environment (PSIM Simulation Software). The energy converters covered four
parts which are solar controller, wind controller, change controller and inverter.
A piecewise linear model is used to model the V-I characteristic of a
photovoltaic array (PV), while a discrete maximum power point tracker (MPPT)
– boost converter is then used to optimizes the match between the PV array
and the load.
Wind controller circuitry comprises a non-inverting buck and boost converter
circuit, where it is tested to receive both DC and AC types wind turbine input.
A simple direct charge controller is implemented to detect battery bank
voltage for charging purposes and disconnect the battery when it is fully
charge.
Lastly, an H-bridge voltage source inverter (VSI) is developed to convert DC
bus voltage of 42Vdc to 230Vrms / 60Hz AC waveform suitable for use with
common electrical appliances.
Overall results obtained are deemed acceptable. However, it is simulated as
individual circuitry with fixed load and not as a fully integrated energy
converter connected to a lead acid battery model.
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Acknowledgement
It has been a quite busy year for me to balance between work, subject study
and capstone project. I would like to thank all of those who have assisted and
supported me in many ways.
Firstly, I would like to thank my capstone project supervisor, Prof. A.I
Maswood for his generous guidance and comments given during my project
of work. Without his fully support that I cannot be completed my project.
I am also grateful to my friend – Mr. Petra Wong for helping me obtaining the
PSIM software, so that I am able to proceed with my simulation without
worrying on the limitations associate with demo version. And he also help me
a lot for circuit design and using of the PSIM.
Also without the Mr. Zeng, I cannot access to the reference books from
National University of Singapore.
Most importantly, I would like to thank my family and friends for their caring
support throughout this year.
Thank you very much.
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List of Figure
Figure 1.1, U.S. Nameplate Capacity and Generation (2008)
Figure 1.2, Top Countries with Installed Renewable Electricity by Technology
Figure 1.3, Stand-Alone PV Energy System
Figure 1.4, Relationship between 3 phases of the charge cycle
Figure 1.5, Square, Modified, and Pure Sine Wave
Figure 1.6, Stand-Alone Wind Energy System
Figure 1.7, a rotor rotates the generator (which is protected by a nacelle)
Figure 1.8, Wind speeds increase with height
Figure 1.9, Stand alone hybrid wind solar energy system
Figure 2.1, Components of Wind Energy System
Figure 2.2, Relationship between Wind Speed and Wind Power
Figure 2.3, Full Bridge Rectifier
Figure 2.4, C-Filter Across rectifier Output
Figure 2.5, parasitic series and shunt resistances in a solar cell circuit
Figure 2.6, I-V Curves of Solar Cell with Effects of Series and Shunt Resi
Figure 2.7, Simple diagram of Photovoltaic Panel with MPPT
Figure 2.8, Maximum Power Point of Photovoltaic Panel
Figure 2.9, Basic Circuit for a Boost Type DC-DC Converter
Figure 2.10, Basic Circuit for a Boost Type DC-DC Converter
Figure 2.11, Synchronous Non Inverting Buck Boost Type DC-DC Converter
Figure 2.12, Voltage Feedback Control
Figure 2.13, Current Feedback Control
Figure 2.14, General Power Converter System
Figure 2.15, Type III Amplifier
Figure 2.16, CCM Inductor Current
Figure 2.17, DCM Inductor Current
Figure 2.18, Single Phase H-Bridge Inverter Topology
Figure 3.1, Integrated Hybrid Wind Solar Energy Converter
Figure 4.1, Simplify I-V Curve in 4 segments
Figure 4.2, 3 Parallel Diode Piecewise Linear Model of PV Array
Figure 4.3, I-V Plot at 1000W/m2 Irradiance Level
Figure 4.4, P-V Plot at 1000W/m2 Irradiance Level
Figure 4.5, Peak to Peak Inductor Ripple Current
Figure 4.6, PV Connected to open Loop MPPT
Figure 4.7, Type III Error Amplifier
Figure 4.8, PV Connected to Closed Loop MPPT
Figure 4.9, Vout and Vpv voltage response at 1000w/m2
Figure 4.10, Ipv and Iout at 1000w/m2
Figure 4.11, Inductor Voltage Response at 1000w/m2
Figure 4.12, Inductor Current response at 1000w/m 2
Figure 4.13, capacitor Ripple Response at 1000w/m2
Figure 4.14, Capacitor Current Response at 1000w/m2
Figure 4.15, Duty Cycle at 1000w/m2
Figure 4.16, Verror Response at 1000w/m2
Figure 4.17, Open Loop Bode plot at 33ohms load with 0.59DC
Figure 4.18, Closed Loop Bode Plot at 33 ohms Load
Figure 4.19, Non-inverting Buck Boost Converter
Figure 4.20, Buck – Boost Mode Selector Circuit
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Figure 4.21, Peak to Peak Inductor Ripple Current
Figure 4.22, Output Voltage Response due to 5.8Vdc input
Figure 4.23, Output Voltage Response due to 41Vdc input
Figure 4.24, Output Voltage Response due to 43Vdc input
Figure 4.25, Output Voltage Response due to 99Vdc input
Figure 4.26, Output Voltage Response due to 30Vpk / 10Hz input
Figure 4.27, Output Voltage Response due to 110Vpk / 100Hz input
Figure 4.28, Wind Controller with Variable Freq & Amp Multiplexer Inputs
Figure 4.29, Scenario 1 Multiplexer’s AC Output
Figure 4.30, Scenario 1 Rectifier and Converter Output
Figure 4.31, Scenario 2 Multiplexer’s AC Output
Figure 4.32, Scenario 1 Rectifier and Converter Output
Figure 4.33, Scenario 3 Multiplexer’s AC Output
Figure 4.34, Scenario 3 Rectifier and Converter Output
Figure 4.35, Charge Controller
Figure 4.36, Vsine vs. Vtri waveform
Figure 4.37, FFT of unipolar PWM signal
Figure 4.38, Vac at unity Power Factor
Figure 4.39, Current Waveform at unity Power Factor
Figure 4.40, Vac at 80% Power factor
Figure 4.41, Current Waveform at 80% Power factor
Figure A.1.1, (I-V Plot) At 800w/m Irradiance Level
Figure A.1.2, (P-V Plot) At 800w/m Irradiance Level
Figure A.1.3, (I-V Plot) At 600w/m Irradiance Level
Figure A.1.4, (P-V Plot) At 600w/m Irradiance Level
Figure A.1.5, (I-V Plot) At 400w/m Irradiance Level
Figure A.1.6, (P-V Plot) At 400w/m Irradiance Level
Figure A.1.7, (I-V Plot) At 200w/m Irradiance Level
Figure A.1.8, (P-V Plot) At 200w/m Irradiance Level
Figure A.2.1, Vout and Vpv Voltage Response at 800w/m2
Figure A.2.2, Vout and Vpv Voltage Response at 600w/m2
Figure A.2.3, Vout and Vpv Voltage Response at 400w/m2
Figure A.2.4, Vout and Vpv Voltage Response at 200w/m2
Figure A.2.5, Inductor Voltage Response at 800w/m 2
Figure A.2.6, Inductor Voltage Response at 600w/m 2
Figure A.2.7, Inductor Voltage Response at 400w/m 2
Figure A.2.8, Inductor Voltage Response at 200w/m 2
Figure A.2.9, Inductor Current Response at 800w/m2
Figure A.2.10, Inductor Voltage Response at 600w/m 2
Figure A.2.11, Inductor Voltage Response at 400w/m 2
Figure A.2.12, Inductor Voltage Response at 200w/m 2
Figure A.2.13, Capacitor Ripple Response at 800w/m 2
Figure A.2.14, Capacitor Ripple Response at 600w/m 2
Figure A.2.15, Capacitor Ripple Response at 400w/m 2
Figure A.2.16, Capacitor Ripple Response at 200w/m2
Figure A.2.17, Capacitor Current Response at 800w/m 2
Figure A.2.18, Capacitor Current Response at 600w/m 2
Figure A.2.19, Capacitor Current Response at 400w/m 2
Figure A.2.20, Capacitor Current Response at 200w/m 2
Figure A.2.21, Duty Cycle at 800w/m2
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Figure A.2.22, Duty Cycle at 600w/m2
Figure A.2.23, Duty Cycle at 400w/m2
Figure A.2.24, Duty Cycle at 200w/m2
Figure A.2.25, Ipv and Iout at 800w/m2
Figure A.2.26, Ipv and Iout at 600w/m2
Figure A.2.27, Ipv and Iout at 400w/m2
Figure A.2.28, Ipv and Iout at 200w/m2
Figure A.2.29, Verror at 800w/m2
Figure A.2.30, Verror at 600w/m2
Figure A.2.31, Verror at 400w/m2
Figure A.2.32, Verror at 200w/m2
Figure A.3.1, Output Voltage Response due to 12Vdc Input
Figure A.3.2, Output Voltage Response due to 24Vdc Input
Figure A.3.3, Output Voltage Response due to 36Vdc Input
Figure A.3.4, Output Voltage Response due to 48Vdc Input
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List of Table
Table 1.1, Advantages and Disadvantages of Solar vs. Wind system
Table 2.1, Comparison of MPPT Algorithm
Table 2.2, P&O Algorithm
Table 2.3, IncCond Algorithm
Table 2.4, Non Inverting Buck – Boost Converter Mode of Operation
Table 4.1, MPPT Input/output Parameters
Table 4.2, Open Loop MPPT Measurement
Table 4.3, Closed Loop MPPT Measurement
Table 4.4, Open Loop Phase / Gain margin at 33 ohms Load
Table 4.5, Close Loop Phase / Gain margin at 33 ohms Load
Table 4.6, Buck – Boost Mode Selection
Table 4.7, Buck Converter Input/output Parameters
Table 4.8, Boost Converter Input/output Parameters
Table 4.9, Charging Truth Table of SR FF
Table 4.10, Estimation of Total Wattage Usage for Inverter
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Chapter One:
1.1
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Investigation of Project Background
Renewable Energy
In today’s society, human race around the world are always hungry for energy.
This form of energy known as electricity is supply to industrial plants,
commercial offices, and residential buildings. Information technology has
been evolving ever since to provide reliable powers source for industrial
machinery, IT gadgets, electrical appliances, street lighting and many more to
help peoples work and live with ease.
Figure 1.1, U.S. Nameplate Capacity and Generation (2008) [1]
Source: Energy Information Administration,
Renewable energy resources [2] include solar energy, geothermal energy,
energy from the wind or waves, energy from tides and energy from biomass.
They are available each year, unlike non-renewable resources which are
eventually depleted. A simple comparison is a coal mine and a forest. While
the forest could be depleted, if it is managed properly it represents a
continuous supply of energy, vs. the coal mine which once it has been
exhausted is gone. Most of earth's available energy resources are renewable
resources. Renewable resources account for more than 93 percent of total
U.S. energy reserves. Annual renewable resources were multiplied times
thirty years for comparison with non-renewable resources. In other words, if
all non-renewable resources were uniformly exhausted in 30 years, they
would only account for 7 percent of available resources each year, if all
available renewable resources were developed.
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Currently human predatory uses of earth resources almost overload more
than 20% of the earth carrying capacity and this amount has also been
increasing yearly by yearly. Base on population growth, economic
development and technological innovation, by 2050, the human will consume
the 180% to 220% of the biological growth capacity on the earth. It means that
unless governments take immediate and appropriate measured use.
Otherwise, by 2030, the index of representing by the average human life
expectancy, educational attainment, and the world economy would show that
the social welfare of humanity will fall [3].
Figure 1.2, Top Countries with Installed Renewable Electricity by Technology
(2008)
Source: Energy Information Administration, REN21, IGA,
As governments work to improve energy security and sustainability,
renewable energy should emerge as an important part of most countries’
portfolios. If supported by appropriate policy frameworks, renewable energy
will contribute to a secure, sustainable and economically competitive energy
sector.
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Solar/Wind Energy Converter System
There are many kind of the renewable source around of us. However, this
project will only concentrate on solar and wind isolated system and below
briefly describe the operation of each type.
1.2.1 Solar Energy Converter System
Typically, a stand-alone Photovoltaic (PV) system consists of 4 components,
namely the Solar panels, Charge controller, Batteries and the Inverter. Each
component functions are described as follows.
Figure 1.3, Stand-Alone PV Energy System
1.2.1.1
Solar (PV) Panel:
Solar panels generate free power from the sun by converting sunlight to
electricity with no moving parts, zero emissions, and no maintenance. The
solar panel, the first component of a electric solar energy system, is a
collection of individual silicon cells that generate electricity from sunlight. PV
can be connected either in series or parallel to achieve higher voltage output
or current output depending on load requirement.
1.2.1.2
Charge Controller:
Since the brighter the sunlight, the more voltage the solar cells produce, the
excessive voltage could damage the batteries. A charge controller is used to
maintain the proper charging voltage on the batteries. As the input voltage
from the solar array rises, the charge controller regulates the charge to the
batteries preventing any overcharging.
1.2.1.3
Batteries:
Battery is to provide storage for excess DC power from PV panel and to
channel it to the load during the night or during a period of low solar radiation.
It can be a single battery or multiple connected together in series for higher
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required voltage and amp-hour capacity. Common batteries uses are of Deep
discharge lead-acid type.
1.2.1.4
Inverter:
An inverter is a device which converts DC power stored in a battery to
standard 120/240 VAC electricity for AC distribution. Inverter basically first,
switched direct current (DC) source back and forth to produce raw alternating
current (AC) and then further transformed, filtered, stepped to make it an
acceptable output waveform. In order to have a quiet and clean AC output,
the DC source has to undergone more processing stages. But, efficiency is
reduced after conversion [4].
Basic inverters output are sine wave and modified sine wave, where the
different is in it efficiency and distortion levels. Sine wave efficiency can reach
up to about 94%, while modified sine wave about 70%. Clearly, modified sine
wave distortion level is higher due to harmonics present and not all device
work properly with it.
Figure 1.5, Square, Modified, and Pure Sine Wave
To produce 240VAC, inverter output can be equipped with a step-up
transformer. Examples of AC loads are lighting, appliances, motors, fans, etc
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1.2.2 Wind Energy Converter System
Similarly, stand alone wind system has more or less the same components
use in a stand-alone PV system. The different is at the input source which is a
wind turbine mounted on a tower.
Figure 1.6, Stand-Alone Wind Energy System
1.2.2.1
Wind Turbine:
A wind turbine [5] is made up of several mechanical parts namely the
propeller like rotor, gear box and generator. Its function is to converts kinetic
energy of the winds motion into mechanical energy transmitted by the shaft,
then into electric energy using generator, thus producing electricity. Wind
turbines are generally categorized into Horizontal axis type and Vertical axis
type. The amount of power is mainly determine by the diameter of it rotor
know as rotor swept area.
Figure 1.7, A rotor rotates the generator (which is protected by a nacelle), as
directed by the tail vane.
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Tower:
The higher the wind tower, the better the wind. Winds closer to the ground are
not only slower, they are also more turbulent. Higher winds are not corrupted
by obstructions on the ground and they are also steadier.
Figure 1.8, Wind speeds increase with height
Tower heights approximately twice to triple the blade length have been found
to balance material costs of the tower against better utilization of the more
expensive active components [6].
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1.2.3 Performance of Solar/Wind Energy System
Despite both methods is pollution free with no greenhouse gases emitted.
Each system has many other distinct advantages and disadvantage between
them and is shown in table.
System
Type
Solar
Electric
Power
System
Advantages












Wind
Electric
Power
System




Disadvantages
Extremely Low maintenance
Simple installation
Reliable long lifespan
Unattended operation
Low recurrent costs
System can be cascaded to
achieve higher output power
Can be used almost anywhere
Predictable power output in
most locations
Silent, unobtrusive operation


Potentially long lasting
Low cost per watt hour in a
good windy site location
low maintenance with smaller
systems
Predictable power output in
some locations
Does not interfere with animals
natural habitat and agriculture
plantation
Able to generate up to mega
watt power of electricity
Excellent supplement to other
renewable sources











Relatively high initial cost
Requires good solar exposure
in the day to achieve
maximum power output
Zero power output in the night
Each PV panel has about 40%
efficiency only
PV panels often replace when
damaged.
High maintenance and costly
repairs for large system
Difficult to find parts
Seasonal disadvantages
Need special tools for
installation
Labor intensive
Towering can be expensive for
larger units, and may require
heavy equipment to erect.
Wind speed is unpredictable
Noise generated in high winds
Table 1.1, Advantages and Disadvantages of Solar vs. Wind system
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Hybrid Solar/Wind Energy Converter System
Both solar and wind systems alone have flaws, where each system must be
optimized to it specific location in order to maximize it usage. However, when
the two systems are combined, they fairly well cover each others' weaknesses,
providing constant and reliable electricity to the consumer.
Figure 1.9, Stand alone hybrid wind solar energy system
How does the system work?
Step 1(a),
electricity.
Sunlight hits the solar module then converts the light into
Step 1(b),
Wind strikes the turbine blades, turning the generator and
turning this energy into electricity.
Step 2,
This electricity travels through wires to the inverter, which takes
the electricity from the solar module or wind generator (DC
electricity) and converts it into the electricity our home needs to
run our appliances, lighting, etc. (AC electricity)
Step 3,
This AC electricity then travels to your standard utility breaker
box, and is supplied to your net meter which then feeds the
electricity both to your home and to the electrical utility grid.
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Chapter 2:
2.1
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Review of Theory and Previous Work
Wind Turbine Power Generation
The power in the wind to drive a wind turbine to produce mechanical power
for electrical power generated. In hybrid energy system, a wind turbine
converts the mechanical energy of wind into electrical energy.
Figure 2.1, Typical components of Wind Energy System
In a wind turbine, the wind pushes against the turbine blades, causing the
rotor to spin...turning the copper armature inside the generator and generating
an electric.
The power available [7] in the wind is proportional to the cube of its speed.
Figure 2.2, Relationship between Wind Speed and Wind Power
2.2
AC – DC Diode Rectifier
There can be two types of input AC source signal which are fixed frequency &
amplitude and varying frequency & amplitude. Normally we are using the
rectifier to converter AC voltage to a DC voltage. Rectifier can be classified
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into 2 type’s base on the AC input: single phase rectifier that is suitable for
many electronic circuits and 3-phase rectifier for high power application or
utilities usage. However, we only discuss the single phase rectifier in here.
Figure 2.3, Signal Phase Full Wave Rectifier
The rectifier converts both positive and negative cycle of the AC input to DC
output via the 4 diodes, where the output voltage when Diodes D1 and D2
conduct is [8]:
v0  Vm sin t For 0  t  
And when D3 and D4 conduct is:
v0  Vm sin t For   t  2
Ignoring the forward voltage drop across the diodes, the secondary
transformer peak voltage is
Vm  2  Vs ,rms
While the average output voltage (DC)
v0( dc ) 
2Vm


2  2 Vs ,rms

A C-filter is connected across the rectifier output to smooth out the pulsating
DC output, creating a near pure DC voltage as shown in below figure.
Figure 2.4, C-Filter Across rectifier Output
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2.3
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Solar Cell Equivalent Circuit
The photovoltaic (PV) power system [9] is building by solar cell. These solar
cells are connected in series or parallel to delivers higher power in the form of
a PV module or PV array. The equivalent electrical circuit of an ideal solar cell
can be treated as a current source parallel with a diode shown in figure.
Figure 2.5, parasitic series and shunt resistances in a solar cell circuit
I-V characteristics of the equivalent solar cell circuit can be determined by
following equations: The current through diode is given by:
 qV 1Rs  
I D  I 0  e KT  1




While, the solar cell output current:
I  I L  I D  I sh
 qV 1Rs   V  IRs
I  I L  I 0  e KT  1 


Rsh


Where,
I
IL
: Solar Cell Current (A)
: Light Generated Current (A)
IO
q
: Diode Saturation Current (A)
T
:
:
:
:
k
V
Rs
Rsh
: Electron Charge (1.6x10-19 C )
Cell Temperature in Kelvin (K)
Bolzman Constant (1.38x1023 J/K)
Solar Cell Output Voltage (V)
Solar Cell Series Resistance (  )
: Solar Cell Shunt Resistance (  )
An ideal solar cell exhibits no series loss and no leakage current to ground,
therefore the series / shunt resistance value is Rs  0 & Rsh   .
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Figure 2.6, I-V Curves of Solar Cell
2.4
Maximum Power Point Tracker (MPPT)
The full name of MPPT controllers [10], “Maximum Power Point Tracker” solar
controller, the new generation products for charging and discharging controller
of solar energy, which means the controller can detect the generating realtime voltage of solar panels and to track the max value of the voltage and
current (VI) to get the highest efficiency of the system. It is essentially a DCDC converter that optimizes the match between the PV modules and the utility
load.
Ipv
DC to DC
Converter
Vpv
Vout
Load
Photovoltaic
Vpv
Ipv
MPPT
Controller
pulses
Figure 2.7, Simple diagram of Photovoltaic Panel with MPPT
Below figure shows the maximum power on the I-V and P-V characteristic,
where V p  max is the maximum output voltage and I p  max is the maximum
output current. Hence, the Max-electrical power is determined
by Pp  max  V p  max  I p  max .
Figure 2.8, Maximum Power Point of Photovoltaic Panel
12
A Hybrid Wind/Solar Energy Converter
2.5
SIM UNIVERSITY
DC – DC Converter
The Direct Current (DC) cannot be stepped up or down via a transformer, not
same as Alternating Current (AC). Therefore, a DC-DC converter is needed
whenever the DC voltage is to be change from one voltage level to another.
This DC–DC conversion method is very useful to power many applications
from an inappropriate DC voltage source directly. However, during the
process of converting DC energy, it is important to keep the power losses
minimum in order to achieve the highest efficiency possible. Using latest
components such as switching MOSFET and Scotty diodes available in the
market, DC–DC converter nowadays can yield an efficiency about 80% to
85%.
2.5.1 Non-Isolated Converter Topology
Basically there are 4 main types of non-isolating converter [11] namely the
Boost, Buck, Buck-Boost and Cuk converter. However, only boost converter,
buck converter and Non-inverting buck-boost converter mode of operation will
be covered in this section:
2.5.1.1
Boost Converter
Boost converter is require when an output voltage greater than the input
voltage is needed. The basic circuit of the boost converter requires 5 basic
components, namely an inductor, power switch, diode, capacitor and a
switching controller and it components placement is shown in below figure.
Figure 2.9, Basic Circuit for a Boost Type DC-DC Converter
In order to step up the voltage, the power switch Q1 is turn ON and OFF at
high frequency. The duration of which Q1 operates follows the duty cycle D
produce by the switching control circuit.
Duty Cycle, D 
ton
1
where T 
T
f switch
13
A Hybrid Wind/Solar Energy Converter
SIM UNIVERSITY
During the ON state, a complete path is form through inductor L and Q1 for
the input current to flows back to Vin. As Vin voltage is applied across L,
energy stores inside L builds up with raising inductor current and the load
current is supplied by the charges in output capacitor C1 alone. The rate of
inductor raise current is express as:
iL Vin

t
L
Where t is the time interval of the duty cycle, D
Therefore, rearranging the equation, the ON state inductor current is,
iL 
Vin
D
L
In the OFF state, L opposes any drop in current by reversing its EMF
immediately, thus, appearing in series with the Vin and adds up to supply the
output.
Output Voltage, Vout  Vin  VL
Inductor Voltage, VL  Vin  Vout
The current inside L now flows through D1 to the load, recharging C1 as well
and then back to Vin. The rate of change in inductor current in the OFF time
interval is,
iL 
Vin  Vout
 1  D 
L
Since the duty cycle D is periodic, the average inductor current must be zero
and the sum of change in inductor current over ON and OFF time interval
should be equal to zero.
LON    LOFF   0
Vin
V  Vout
 D  in
 1  D   0
L
L
Simplifying the equation leads to output voltage equation:
Vout 
Vin
T
 Vin
Or Vout 
1 D
tOFF
The value of D is varies in the range of 0 < D < 1. The lowest output voltage
value is when D = 0, which the output voltage equals Vin and when D
approaches unity, the output voltage tends to infinity.
14
A Hybrid Wind/Solar Energy Converter
2.5.1.2
SIM UNIVERSITY
Buck Converter
Buck converter components elements are the same as the Boost converter,
except the arrangement of the power switch, Inductor and diode are slightly
different. Again the operation consists of varying the switching duty cycle of
the power switch to obtain desire output voltage. However, this time is to step
down from a higher voltage to a lower voltage. Below shows the schematic of
the buck converter:
Figure 2.10, Basic Circuit for a Buck Type DC-DC Converter
When Q1 is in the ON state, D1 is in reserve bias and thus open, current
starts to flow from Vin through the inductor L and into C1 and the load. The
rate of rising inductor current is,
iL 
Vin  Vout
D
L
In the OFF state, L reverse its voltage to fight the collapsing magnetic field,
and thus D1 is activated as a freewheeling diode for the inductive current too
continues circulating through C1 and the load. The rate of decreasing inductor
current is as follows:
iL 
Vout
 1  D 
L
Since the average inductor voltage is null over both ON and OFF time interval,
LON    LOFF   0
Vin  Vout
 V

 D    out  1  D    0

L

  L

Simplifying the equation leads to output voltage equation: Vout  Vin  D Or
Vout  Vin 
tON
T
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A Hybrid Wind/Solar Energy Converter
SIM UNIVERSITY
It is clear that the output voltage depends directly on the duty cycle. If the duty
cycle is 50%, output voltage will be one half of the input voltage.
2.5.1.3
Non Inverting Buck-Boost Converter
This topology is a cascading combination of a buck converter followed by a
boost converter, where by the inductor L is shared. As the name already
implies, this topology inherit both mode of operation from the buck converter
and boost converter. Therefore, it’s has ability to work over a wide range of
input voltage to generate both higher and lower voltages. Furthermore, output
voltage polarity is of the same as input voltage, unlike traditional buck-boost
converter which is inverting of each other. Synchronous non inverting buck
boost converter schematic is much more complex and is show in below figure.
Figure 2.11, Synchronous Non Inverting Buck Boost Type DC-DC Converter
Depending on the input and output voltages, either the buck mode or boost
mode can be achieved via careful controlling of the 4 power switches. The
activity of each power switch is listed in the table.
Duty
Q1
Q2
Q3
Q4
Type
Cycle
On-Off
On-Off
Complimentarily
Complimentarily
Vin=Vout
Always On
Always Off
Vin<Vout
Always On
Always Off
Vin>Vout
Always Off
Always On
< 0.5
Always Off
Always On
= 0.5
On-Off
On-Off
Complimentarily
Complimentarily
> 0.5
Buck
Boost
Table 2.4, Non Inverting Buck – Boost Converter Mode of Operation
Since this topology is a cascade of 2 individual converters back to back, the
overall dc transfer ratio can be determined as follows:
16
A Hybrid Wind/Solar Energy Converter
SIM UNIVERSITY
Vout
 M  D   M buck  D   M boost  D 
Vin
Vout
1
 D
Vin
1 D
 D 
Vout  
  Vin
 1 D 
2.6
DC – AC Inverter
Most modern inverters in the market offer 2 types of AC output – modified
sine wave and pure sine wave, where the first type usually has much cheaper
cost then the latter. Unlike modified sine wave, pure sine wave inverter is a
more preferred choice, as almost all electronics equipments have no
problems working with it. For this reason, utility company supplies single
phase pure sine wave power for homes usage.
Generally, inverters circuit employs the H-bridge topology for voltage
conversion as shown in figure. To achieve a good approximation of a sine
wave output, a simple and yet efficient method known as the pulse width
modulation is used. A comparator compares a reference 50/60Hz sine wave
with a high frequency carrier ramp waveform, to generate a variable duty
cycle signal for controlling the 4 power switches. This PWM signal is feed to
switch S1 / S4 pair, while S2 / S3 pair receives the inverted PWM signal
instead. A passive L-C filter is then required to remove the high frequency
carrier of the PWM signal.
Figure 2.18, Single Phase H-Bridge Inverter Topology
In order to reconstruct the output AC waveform correctly at the load, the PWM
modulator must sample the DC voltage that falls within range of modulation
amplitude. For ma value less than 1, rms output voltage value will decrease
linearly, as the PWM on-times pulses get proportionally smaller. If ma is
greater than 1, over modulation occurs as the PWM on-time pulses gradually
merges to become a square wave, resulting in multiples harmonics of the
carrier frequency appearing at the output.
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SIM UNIVERSITY
Amplitude Modulation Ratio, ma 
Vcontrol
Vtri
Frequency modulation defines the ratio of the ramp carrier frequency to the
reference sine wave. As long as mf is large, filtering of unwanted high
frequency components at the load will be easy, leaving only the desired
reference sine wave component at the output load.
Frequency Modulation Ratio, mf 
18
f tri
f control
A Hybrid Wind/Solar Energy Converter
Chapter 3:
3.1
SIM UNIVERSITY
Project Management
Project Objective
Among alternative energy sources, wind and solar energies have good
prospects for both isolated load and grid interconnection. These two energy
sources also complement to each other. Considering the high cost of
electrical energy available from these sources. It is worthwhile to economies
in its capital cost. An integrated wind/solar converter can be very attractive is
such a case.
The project will concentrate in doing that, which will start from literature
search, conduct comparative study with isolated system, develop models and
finally propose some viable topologies.
3.2
Overall Objective
The rising number of people opting for production and storage of solar energy
for power is showing a positive graph in prevention of further aggravation of
the depleted natural resources. Another cause for the demand for harnessing
of solar energy and wind energy to suffice the daily needs is the increasing
expenses which is cause of great concern.
Among alternative energy sources, wind and solar energies have good
prospects for both isolated load and grid interconnection. However, the solar
energy and wind energy as stand-alone systems are not the best options.
There are times when the sun does not shine and cloudy skies may linger for
days. There are even times when the wind does not blow to help propel the
powering systems. At such times the hybrid wind and solar systems is the
most effective solution to meet our power demands.
Since a hybrid wind/solar system provides stable output and minimize the
dependence of the output upon seasonal changes, it can be deployed in both
large scale to small scale application ranging from mega wattage power plant
providing electricity to millions of households/office building in a large city,
self-sustainable homes/farms in sub-urban/rural areas and to simple urban
cities streets lighting, billboards or signage.
Micro or mini wind turbines combined with solar arrays are an ideal solution
for "off the grid systems". Used together they add an enormous amount of
reliability to the system, but are also more cost effective.
Although wind/solar energy sources is abundant and environmental friendly.
In current situation, the use of small scale renewable energy is not cost
effective compared to energy supplied via a mains electricity supply network.
Considering the high cost of electrical energy available from these sources, it
is worthwhile to economies in its capital cost. It is therefore important to
19
A Hybrid Wind/Solar Energy Converter
SIM UNIVERSITY
construct an integrated hybrid wind /solar energy converter through simulation
that helps achieve low unit costs.
3.3
Project Outline
This project will begins by gathering information through literature search on
the power electronics circuitry used in this hybrid energy converter and later
concentrate in the development of each power converter block using PSIM
simulation software.
Types of energy converter to construct are:

AC-DC converter to convert wind generator AC output to 42VDC DCbus

DC-DC converter to step up low solar output to 42VDC DC-bus

Charge controller to detects battery bank voltage for charging purposes

DC-AC inverter to convert 42VDC DC-bus to 230VAC/60Hz output for
utility use
Controller
AC Loads
230V
AC-DC
Diode
Rectifier
Wind Turbine
42V DC
DC-AC
Inverter
DC Loads
42V
MPPT
Controller
PV Modules
Charge Controller
Integrated Hybrid
Wind/Solar Energy Converter
42V DC
Battery Banks
Figure 3.1, Block diagram of a Hybrid Wind Solar Energy Converter
20
A Hybrid Wind/Solar Energy Converter
3.4
SIM UNIVERSITY
Project Circuit Design Flow Chart
Yes
No
No
Yes
21
A Hybrid Wind/Solar Energy Converter
Gantt Chart
1
Capstone Commencement
2
Define the Project Objective
3
Initial the Project Plan
4
Scheduling the Project
5
Study the PSIM Simulation Software
6
Investigative and Integrative of the Project
7
Project Proposal Preparation/Submission
8
Define Hybrid Energy Converter Circuit Block
9
Study the Solar Cell Characteristic
10
Study the Maximum Power point Tracker (MPPT)
11
Study the Power Electronics Converters Toplolgy
12
Study the Stability and Compensation for Converters
13
Design the Solar Controller Using PSIM
14
Modeling of Photovoltaic Panel
15
Simulation of Boost MPPT (open loop & close loop)
16
Initial Simulation of Circuit
17
Poject Interim Report Preparation/Submission
18
Study the Turbine/Lead Acid Battery Equiralent Circuit Model
19
Simple Modeling of Wind Generator Output Using Multiplexer
20
Simulation of Wind Controller with Multiplexer Output
21
Design the Wind Controller Using PSIM
22
Simulation of Buck Boost Mode Selector
23
Simulation of Non-Inverting Back Boost Converter
24
Design the AC-DC Diode Rectifier Converter Using PSIM
25
Hybrid Analysis the Wind/Solar Energy
26
Supply to Real Word Problem (2KW Load)
27
Design the Simple Charge Controller Using PSIM
28
Design of DC-AC Inverter Using PSIM
29
Simulation of Inverter to Achieve 230Vac/50Hz Output
30
Final Simulation/Conclusion/Summaries/Recommendation
31
Suggestion for Furture Work
32
Critical Review and Reflections
33
Compilation of Thesis/Final Report Submission
34
Material Preparation for Poster Presentation/Q&A
22
23 Nov ~ 28 Nov
22 Nov ~ 28 Nov
15 Nov ~ 21 Nov
8 Nov ~ 14 Nov
01 Nov ~ 07 Nov
25 Oct ~ 31 Oct
Nov-10
18 Oct ~ 24 Oct
11 Oct ~ 17 Oct
04 Oct ~ 10 Oct
27 Sep ~ 03 Oct
Oct-10
20 Sep ~ 26 Sep
13 Sep ~ 19 Sep
06 Sep ~ 12 Sep
30 Aug ~ 05 Sep
23 Aug ~ 29 Aug
Sep-10
16 Aug ~ 22 Aug
09 Aug ~ 15 Aug
02 Aug ~ 08 Aug
26 Jul ~ 01 Aug
19 Jul ~ 25 Jul
Aug-10
12 Jul ~ 18 Jul
05 Jul ~ 11 Jul
29 Jun ~ 04 Jul
28 Jun ~ 04 Jul
Jul-10
21 Jun ~ 27 Jun
14 Jun ~ 20 Jun
07 Jun ~ 13 Jun
31 May ~ 06 Jun
24 May ~ 30 May
Jun-10
17 May ~ 23 May
10 May ~ 16 May
03 May ~ 09 May
26 Apr ~ 02 May
May-10
19 Apr ~ 25 Apr
12 Apr ~ 18 Apr
05 Apr ~ 11 Apr
29 Mar ~ 04 Apr
Apr-10
22 Mar ~ 28 Mar
15 Mar ~ 21 Mar
01 Mar ~ 07 Mar
Mar-10
22 Feb ~ 28 Feb
15 Feb ~ 21 Feb
08 Feb ~ 14 Feb
S/N
01 Feb ~ 07 Feb
Feb-10
Activities Task
Description
08 Mar ~ 14 Mar
3.5
SIM UNIVERSITY
A Hybrid Wind/Solar Energy Converter
Chapter 4:
4.1
SIM UNIVERSITY
Design and Simulation
Design of Solar Controller
4.1.1 Modeling of Photovoltaic Panel
Basically, the I-V curve of a PV array can be divided into 4 segments as in
below figure [12]. A simple 3 parallel diode piecewise linear model is used to
substitute the single diode of the equivalent solar cell circuit.
Figure 4.1, Simplify I-V Curve in 4 segments
Each diode purpose is to act as a 2 state voltage controlled resistor to
approximate each individual line segment.
Figure 4.2, 3 Parallel Diode Piecewise Linear Model of PV Array
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A Hybrid Wind/Solar Energy Converter
SIM UNIVERSITY
Figure shows the plots obtain through simulation for irradiance level of
1000W/m2.
Figure 4.3, I-V Plot at 1000W/m2 Irradiance Level
Figure 4.4, P-V Plot at 1000W/m2 Irradiance Level
24
A Hybrid Wind/Solar Energy Converter
SIM UNIVERSITY
4.1.2 Design the Boost MPPT - Open Loop
Below lists the specifications which the Boost converter will be operating in
the continuous conduction mode (CCM) [13]:
Vin, min
3V
V , Vripple
250mV
Vin, max
21V
Vout, drop
0.5V
Vout
42V
 , efficiency
90% or 0.9
fs
2MHz (Ts=500nsec)
 Ir, current ripple factor
10% or 0.1
Table 4.1, MPPT Input/output Parameters
Given that boost converter output voltage is determine from Vout 
by re-arranging the equation yields the duty cycle D  1 
Vin
and
1 D
 Vin
.
Vin Vout

Vout
Vout
Therefore, the PWM maximum and minimum duty cycle require to obtain
desired Vout with respect to Vin requirement are as follow:
V V
42  21
Dmin  out in ,max 
 0.5
Vout
42
Vout  Vin ,min
42  3
 0.929
Vout
42
I
As the peak inductor current is define by I peak  I L ,avg  L , where I L ,avg  I in ,avg
2
Dmax 

Figure 4.5, Peak to Peak Inductor Ripple Current
Where I L represent the peak to peak inductor ripple current of the close
state power switch,
I L 
Vin DTsw Vin D

L
Fsw L
25
A Hybrid Wind/Solar Energy Converter
SIM UNIVERSITY
Linking I L equation to the average input current by a ripple value  I r .
Vin D
I L

  Ir
Iin,avg Iin,avg Fsw L
And knowing that efficiency,  
Pout Vout I out
. Where

Pin Vin Iin,avg
Pout  42.26V 1.28 A  54W Substituting, I in ,avg to  I r equation, yields
Vin2 D
I L
 Ir 

I in ,avg Pout Fsw L
They require inductor value that satisfy pre-define parameters is.
L
Vin2 Dmin 0.9  212  0.5

 18.38uH
Pout Fsw I r 54  2M  0.1
Choose standard value of 18uH for Power Inductor
Maximum peak inductor current, I peak at Vin ,min and Vin ,max are as follow:
Vin,min Dmax
Pout
54
3  0.929




 20.04 A
in ,min 
Vin ,min
2 LFsw
3  0.9 2 18u  2M
I peak V
I peak V
in ,max
P
out

 V
in ,max
Vin,max Dmin
2 LFsw

54
21 0.5

 3.003 A
21 0.9 2 18u  2M
The output capacitance can be evaluated using V 
Tsw DVout
, where
Rload Cout
Rload  33 at 1000w/m2.
Therefore, Cout required fulfilling the output ripple requirement without ESR.
Cout 
DminVout
0.5  42V

 1.27uF
Fsw Rload V 2M  33  250mV
Let Cout=47uF, where as long as the RC time constant is very much larger
than the On period of the power switch, the output voltage will remain
constant at desired value with less fluctuation.
Below figure shows how the open loop MPPT is connected to the PV model
for voltage and current measurement.
26
A Hybrid Wind/Solar Energy Converter
SIM UNIVERSITY
Figure 4.6, PV Connected to open Loop MPPT
Voltage and current measurement are recorded in below table. It’s easy to
notice the simulated Vpv and Ipv results are lower than the calculated, thus PV
model did not operate at the desire MPP but close concluded to have
achieved it objective.
PV Array
Irradiance
Level
Vpv
Ipv
MPPT
Ppv
Vout
Iout
Pout
DC
Rload
1000W/m2
16.353 2.949 48.224
39.89
1.2087 42.215 0.59
33
800W/m2
16.395 2.379
39.99
0.975
38.99
0.59
41
600W/m2
16.508 1.787 29.499 40.268
0.732
29.476 0.59
55
400W/m2
16.555 1.146 18.972 40.386
0.47
18.965 0.59
86
200W/m2
16.829 0.543
0.222
9.108
185
39
9.135
41.049
0.59
Table 4.2, Open Loop MPPT Measurement
4.1.3 Design the Boost MPPT – Close Loop
In this section, the square wave generator is replaced with a compensation
circuitry to generate the desired duty cycle. However, operating the boost
converter in the CCM region will exhibit a right hand plane zero effect. The
RHPZ has a rising gain characteristic but with a 90o phase lag and where it
frequency location is define by
RHPZ
R 1  D 
 load
L
2
As the RPHZ frequency position changes with duty cycle, it is a must to
determine it high and low RPHZ frequency location in order to compensate it
phase lag in the error amplifier,
27
A Hybrid Wind/Solar Energy Converter
SIM UNIVERSITY
f RHPZ ,low
R 1  Dmax 
33  1  0.929 
 load

 1471.63Hz
2 L
6.28 18u
f RHPZ ,high
R 1  Dma in 
33  1  0.5 
 load

 72.983Hz
2 L
6.28 18u
2
2
2
2
The LC output filter also give rise to a double pole that has a -180o phase shift
and it resonant frequency point is determine by
f LC 
1
2 LC
However, the resonant frequency will follow the input voltage range. Hence
f o,high
1  Dmax
1  0.929
 388.5Hz
2 LC 2 18u  47u
1  Dmin
1  0.5


 2735.93Hz
2 LC 2 18u  47u
f o,low 

To stabilize a boost converter, a type 3 compensation error amplifier [14] is
needed.
Figure 4.7, Type III Error Amplifier
In order to produce duty cycle of 0.59 from 5V ramp amplitude, a feedback
voltage of 2.95V is require from the feedback resistor divider.
Va  DC  5V  0.59  5V  2.95V
Setting R lower value to 10k , R lower resistor value requires is,
Rupper 
10k  42V
 10k  132.37k 
2.95V
The current drawn from this feedback resistor divider can be calculated,
28
A Hybrid Wind/Solar Energy Converter
SIM UNIVERSITY
I R _ lower 
Va
2.95

 295uA
Rlower 10k
I R _ upper 
Vout  Va 42  2.95

 295.83uA
Rupper
132k
Using superposition theorem, the error voltage can be determine by
subtracting error amplifier positive input terminal to the negative input terminal
  V    input  V    input


R2
R
Verror  Vref 
 1  2 Vout
R
 R
upper
 upper Rlower

Let R2  10k  ,
 10k
 10k
Verror  2.5V 
 1 
 42V
 132k 10k  132k
 5.1894V  3.182V
 2.01V
The PWM comparator is of inverting configuration, where it off duration is
given by
1 D 
2.01V
 0.402
5V
Checking boost converter output voltage,
1 D 
Vout 
toff
Ts
Vin  Ts 17.4V

 43.28V
toff
0.402
Assuming C2 << C1 and R3 << Rupper, the remaining compensation network
components value can be work out as follows:
1st zero placing at f o ,low  380 Hz
z 2 
C3 
1
Rupper C3
1
2 Rupper f o ,low

1
 2.652nF
6.28 158k  380
2nd zero placing at 800Hz for system to exhibits critical damp response,
29
A Hybrid Wind/Solar Energy Converter
 z1 
C1 
SIM UNIVERSITY
1
R2C1
1
1

 19.904nF
2 R2 f o ,low 6.28 10k  800
A double poles is also place near RHPZ zero frequency f RHPZ,low , in this case
1400Hz to force the gain to roll off keeping minimum bandwidth to avoid
unwanted noise frequency pick up.
p2 
1
1

 11.37 nF
2 R2 f RHPZ ,low 6.28 10k 1400
C2 
 p1 
R3 
1
R2C2
1
R3C3
1
1

 42.89k 
2 C3 f RHPZ ,low 6.28  2.652n 1400
Below figure shows the closed loop boost MPPT with the compensation dircuit
added.
Figure 4.8, PV Connected to Closed Loop MPPT
30
A Hybrid Wind/Solar Energy Converter
SIM UNIVERSITY
The voltage and current measurement is recorded in below table.
PV Array
Irradiance
Level
Vpv
Ipv
1000W/m2
17.591 2.456
800W/m2
MPPT
Ppv
43.2
Vout
Iout
Pout
DC
Rload
37.714 1.143 43.103 0.534
33
17.55
2.018 35.416 38.052 0.928 35.316 0.539
41
600W/m2
17.548
1.51
26.487 38.105 0.693 26.407 0.539
55
400W/m2
17.57
0.956
16.79
37.896 0.441 16.712 0.536
86
200W/m2
17.26
0.507
8.75
40.03
185
0.216
8.658
0.539
Table 4.3, Closed Loop MPPT Measurement
4.1.4 Closed Loop MPPT Waveform Simulation
Below plots shows the voltage and current response of the MPPT output
(From figure 4.8, circuit of PV connected to close loop MPPT), capacitor and
inductor waveform at 1000w/m2 irradiance level, while other irradiance level
plots are attach in the appendix.
Figure verify that the MPPT circuit is able to extract MPP of ~ 17.5V from the
PV model and maintain steady state output at 37.7V when the sun is shining
at it maximum irradiance level.
Figure 4.9, Vout and Vpv voltage response at 1000w/m2
Below current response plot shows that Ipv is reduce 2.46A from the Isc current
of 3.31A when tracking to it MPP and MPPT output current is stable at 1.14A.
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Figure 4.10, Ipv and Iout at 1000w/m2
The inductor voltage is switch between +17.5V MPP and -20V PV open
voltage.
Figure 4.11, Inductor Voltage Response at 1000w/m2
The inductor current is approximately 2.60A peak when the MPPT is
operating at 1000w/m2 irradiance level.
Vin,max Dmin 17.59  2.456 17.59  0.59
Pout




 2.6 A
in ,max 
Vin,max
2 LFsw
17.59
2 18u  2M
I peak V
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Figure 4.12, Inductor Current response at 1000w/m2
The capacitor ripple voltage is less than 10mV due to the use of 47uF
capacitor value.
V 
DminVout
0.59  37.714V

 7.173mV
Fsw Rload Cout 2M  33  47uF
Figure 4.13, Capacitor Ripple Response at 1000w/m2
The rms current flowing in the output capacitor can be defined using below
formula:
ICout rms  I out
D D  D' RLTsw 
0.59 0.59  0.41 33  500ns 
 

  1.143

  1.3799 A
'
D 12  L 
0.41 12 
18uH

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Figure 4.14, Capacitor Current Response at 1000w/m2
The duty cycle is compute using 50% rising and falling transition timing
(estimation):
DC 
31529.9us  31529.6us 300ns

 0.6
31530.1us  31529.6us 500ns
Figure 4.15, Duty Cycle at 1000w/m2
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Design of Wind Power Controller
Most wind turbine less than 700W in the current market comes in either AC or
DC output option. The wind controller design here will support both option
using the same hardware circuitry by populating/de-populating certain
components and connectors [15]. To support AC WTG, isolation transformer
(T1) and bridge rectifier (BD11) will be populated, while these components will
be de-populated in the DC WTG output version.
** T1 & BD11 only
populated in AC
output WTD version.
Figure 4.19, Non-inverting Buck Boost Converter
4.2.1
Design of Buck – Boost Mode Selector Circuit
The non-inverting buck-boost converter will be design to operate either in
buck mode alone or boost mode alone each having their own compensation
network and feedback path.
The non-inverting buck boost converter power switches operation can be
summaries in below table, while mode selector circuit is show at below figure.
Mode M_S
Vrect > 42V
Buck
0
Vrect < 42V Boost
1
Q1
Q2
Q_Buck QB_Buck
ON
OFF
Q3
Q4
OFF
ON
Q_Boost QB_Boost
Table 4.6, Buck – Boost Mode Selection
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Figure 4.20, Buck – Boost Mode Selector Circuit
4.2.2 Design of Buck Converter
Below lists the specifications which the buck converter will be operating in the
continuous conduction mode (CCM):
Vin, min
43Vdc (48Vrms)
Vramp
5V
Vin, max
99Vdc (110Vrms)
 , efficiency
90% or 0.9
Vout
42Vdc
 Ir, current ripple factor
10% or 0.1
Iout, max
2A
fs, switching frequency
2MHz (Ts=500nsec)
Table 4.7, Buck Converter Input/output Parameters
Given the buck converter output voltage is determine by V out = Vin*D.
Therefore, the PWM maximum and minimum duty cycle require to obtain
desired Vout with respect to Vin requirement are:
Dmin 
Vout
42

 0.4242
Vin ,max 99
Dmax 
Vout
42

 0.9767
Vin ,min 43
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As the peak inductor current is define by I peak  I L ,avg 
I L
, where I out  I L ,avg
2
Figure 4.21, Peak to Peak Inductor Ripple Current
Where I L represent the peak to peak inductor ripple current of the close
state power switch.
I L 
Vout 1  D  Tsw Vout 1  D 

L
Fsw L
Linking I L equation to the output current by a ripple value,  I r .
I L Vout 1  D 

  Ir
I out
I out Fsw L
The inductor value require to achieve 90% efficiency is,
L
Vout 1  Dmin  0.9  42  1  0.424 

 54.43uH
I out Fsw I r
2  2M  0.1
Choose standard value of 56uH for Power Inductor.
Maximum peak inductor current, I peak at Dmin and Dmax are as follow:
I peak  Dmin   I out 
I peak  Dmax   I out 
Vout 1  Dmin 
42  1  0.424 
 2
 2.108 A
2 LFsw
2  56u  2M
Vout 1  Dmin 
42  1  0.977 
 2
 2.0043 A
2 LFsw
2  56u  2M
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4.2.3 Design of Boost Converter
Below lists the specifications which the boost converter will be operating in the
continuous conduction mode (CCM):
Vin, min
2.5Vdc (2.7Vrms)
Vramp
5V
Vin, max
41Vdc
(45.54Vrms)
 , efficiency
90% or 0.9
Vout
42V
 Ir, current ripple factor
10% or 0.1
Iout, max
2A
fs, switching frequency
2MHz (Ts=500nsec)
Table 4.8, Boost Converter Input/output Parameters
Require PWM maximum and minimum duty cycles of boost converter is:
Dmin 
Dmax 
Vout  Vin ,max
Vout
Vout  Vin ,min
Vout

42  41
 0.024
42

42  2.5
 0.94
42
The boost compensation network components value can be calculated using
the L=56uH and C=4700uF value use in buck converter earlier, as they are
shared in this non-inverting buck boost topology.
The maximum peak inductor current, I peak at Vin ,min and Vin ,max are as follows:
Vin,min Dmax
Pout
84
2.5  0.94




 37.34 A
in ,min 
Vin,min
2 LFsw
2.5  0.9 2  56u  2M
I peak V
Vin,max Dmin
Pout
84
41 0.94




 2.28 A
in ,max 
Vin,max
2 LFsw
41 0.9 2  56u  2M
I peak V
While the high and low RPHZ frequency positions are:
f RHPZ ,low
R (1  Dmax ) 2 21 1  0.94 
 load

 214.97 Hz
2 L
2  3.14  56u
f RHPZ ,high
R (1  Dmin ) 2 21 1  0.024 
 load

 56.88 Hz
2 L
2  3.14  56u
2
2
And the resonant frequency due to the input voltage hence is:
f o,high
1  Dmax
1  0.94
 18.62 Hz
2 LC 2  3.14  56u  4700u
1  Dmin
1  0.024


 302.93Hz
2 LC 2  3.14  56u  4700u
f o,low 

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A double zero is place near resonant frequency with maximum duty cycle
value:
1st zero placing at f 0,low  18Hz
z 2 
C3 
1
2 Rupper f 0,low

1
Rupper C3
1
 55.99nF
2  3.14 158k 18
2nd zero placing at f o ,high  40 Hz
 z1 
C1 
1
R2C1
1
1

 398.09nF
2 R2 f 0,low 2  3.14 10k  40
A double pole is placed near RHPZ zero frequency f RHPZ ,low
Double pole placing at f RHPZ ,low  200 Hz
 p2 
C2 
1
1

 79.62nF
2 R2 f RHPZ ,low 2  3.14 10k  200
 p1 
R3 
1
R2C2
1
R3C3
1
1

 14.22
2 C3 f RHPZ ,low 2  3.14 10n  200
The full wind controller schematic can be found at appendix.
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4.2.4 Wind Converter Simulation with DC type WTG
Below simulation plot shows that the minimum DC voltage requirement for
boosting is 5.8V, while it output voltage response is illustrate in below figure.
Figure 4.22, Output Voltage Response due to 5.8Vdc input
At maximum input of 41V, the output response shows signs of oscillation.
Figure 4.23, Output Voltage Response due to 41Vdc input
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Below figure illustrate the output response at 43V minimum and 99V
maximum for buck operation. The output voltage is stable and constant at 42V.
Figure 4.24, Output Voltage Response due to 43Vdc input
Figure 4.25, Output Voltage Response due to 99Vdc input
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4.2.5 Wind Converter Simulation with AC type WTG
Assuming the WTG generator output frequency range from 0 ~ 100Hz with
variable amplitude (circuit refer to figure 4.19).
Figure 4.26, Output Voltage Response due to 30Vpk / 10Hz input
The output response due to 110Vpk at constant 100Hz is shown in figure. A
clean 42V output voltage is achieved with better regulation output from the
bridge rectifier.
Figure 4.27, Output Voltage Response due to 110Vpk / 100Hz input
Wind turbine wild AC output depends on wind’s velocity, which is a variable
frequency variable amplitude waveform. A simple multiplexer circuit is
proposed here to simulate different time interval when the wind turbine
produces different wind conditions.
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Figure 4.28, Wind Controller with Variable Frequency & Amplitude Multiplexer
Inputs
Scenario 1 tries to simulate partial windy condition, where both multiplexer
output and converter output as following:
Figure 4.29, Scenario 1 Multiplexer’s AC Output
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Figure 4.30, Scenario 1 Rectifier and Converter Output
Scenario 2 simulates wind conditions that starts from gentle to strong and
fade away.
Figure 4.31, Scenario 2 Multiplexer’s AC Output
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Figure 4.32, Scenario 1 Rectifier and Converter Output
Scenario 3 simulates frequent strong fading wind at short duration.
Figure 4.33, Scenario 3 Multiplexer’s AC Output
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Figure 4.34, Scenario 3 Rectifier and Converter Output
4.3
Design of Charge Controller
A simple charge controller circuit is constructed below to detects battery bank
voltage and charges it when battery voltage falls below if full charge value.
The amount of charging current from DC bus depends on the output of
wind/solar controller, if the output current is too low, the battery bank may take
too long to charge to maximum. The battery bank permanently connected to
the inverter block and also directly to DC loads [16].
Figure 4.35, Charge Controller
The battery bank consists of seven 6V/20AH lead acid battery connected in
series to from 42V nominal voltage. Full charge condition is reach when
battery voltage is 50.4V (7.2V ~ 7.35V for a single 6V battery). Below table
summaries this charge controller operations.
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S
R
Q
Q_Bar
Relay
Status
LED
Indicator
Remarks
Vbatt < 50.4V
1
0
1
0
Close
Off
Charging
Vbatt > 50.4V
0
1
0
1
Open
On
Battery Full
Table 4.9, Charging Truth Table of SR FF
4.4
Design of Inverter
A maximum power of 350W micro wind turbine is selected for used in this
project. Assuming 25W power losses in system due to cabling and power
electronics components, an inverter specification of 325W / 230Vrms / 60Hz is
to be design. Below table shows the list of common electrical appliances that
can be power from inverter directly.
Items
Wattage
Lighting
Portable Radio / Clock
Satellite Dish
Ceiling Fan
Computer
Freezer
TV
Total:
72W (18W x 4)
10W
30W
40W
50W
50W
70W
322W
Table 4.10, Estimation of Total Wattage Usage for Inverter
In order to reconstruct the AC waveform correctly at the transformer output,
the PWM modulator must sample the DC voltage that falls within range of
modulation amplitude, 0  ma  1 .
V
0.8
 0.8
Amplitude Modulation Ratio, ma  sin e 
Vtri
1
Frequency Modulation Ration, mf 
ftri 10k

 166.667  167
fsin e 60
Figure 4.36, Vsine vs. Vtri waveform
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The peak voltage of the 60Hz / 230Vrms AC is:
Vrms 
Vm  Vrms
Vm
s
2
2  230  2  325.27V
The turn ratio of the power transformer required to achieve 230Vrms on the
secondary is thus:
VS  Vm 
Vs  Vm 
NS
Vp
NP
N s 325.27

 7.744
Np
42
Setting Ns to be 230 turn, therefore, Np is:
Np 
230
 29.69  29 Turns
7.744
Assuming power factor, cos  1 , the inverter current can be found as follow:
P  IV cos
I
P 325

 1.413 Arms
V 230
While the overall impedance require for the load is:
Z
V
230

 162.77
I 1.413
Figure 4.37, FFT of unipolar PWM signal
The cut off frequency is set to 70Hz, therefore, the inductor value require with
a capacitor value of 16uF is:
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f 
f 
1
 2 f 
2

C
1
2 LC
1
 2  70 
2
16u
 323mH
The resultant inverter AC output is thus show below, where instantaneous
voltage peak is
Vm  Vrms  2  230  2  325.26V
Figure 4.38, Voltage Waveform at unity Power Factor
In a pure resistive circuit, current is in phase with the voltage output. It can be
seen from the plot that the AC instantaneous current peak value tally with the
calculation of
I m  I rms  2  1.413 2  1.998 A
Figure 4.39, Current Waveform at unity Power Factor
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However, in practical AC circuit. Unity power factor is hard to achieve,
therefore, a simulation of 80% power factor is also illustrate as follow:
The inductance value can be determined with the resistance value found
earlier:
cos  
Z
R
Z
163
 210
0.8
Z  R 2  XL2
L
Z 2  R2

2 f
 210   163
2  70 
2
2
 301mH
And the current flowing through this new impedance is,
I
V 230

 1.095 Arms
Z 210
The resultant inverter AC output is thus show below:
Figure 4.40, Vac at 80% Power factor
The new instantaneous current is I m  I rms  2  1.095  2  1.549 A
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Figure 4.41, Current Waveform at 80% Power factor
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Chapter 5 Summary, Conclusions and Future Work
5.1
Conclusion
This study presents an integrated hybrid solar wind energy converter, where
each circuit models is simulated using PSIM. The simulations results obtained
are considered acceptable.
The PV model employs in this paper is based on simulation of a single
photovoltaic panel. The model also takes into consideration on the effects of
series and parallel resistances, in order to provide a more accurate I-V
characteristic as possible.
The design of MPPT first calculates the matching load impedance to achieve
MPP using a boost converter and is later verified by using of open loop
method to determine its functionality. A discrete PWM circuit is then
implemented to generate the duty cycle as a closed loop system.
Measurements indicate that PV model are operating at its MPP.
To accommodate usage of both DC and AC type WTG, a non-inverting buck
boost converter is implemented as the core of the wind controller. In DC input
simulation, boost converter accepts voltage range of 5.8V to 41V, while buck
converter is 43V to 99V. Simulated results shows oscillation occurs at 36V or
greater in boost mode. In AC input simulation, it is easy to notice that a high
voltage spike occurs whenever they probably is due to the slow response of
the voltage mode control PWM, as the output voltage have to be sense first
and change accordingly. To eliminate this problem, implementing a soft
switching circuit might helps.
The charge controller implemented here is a simple, low cost but lacks the
monitoring feature of battery’s charging / de-charging status. During charging
process, each solar / wind source will contributes whatever current it’s
capable of producing. Although the battery bank is another critical component,
it is not cover here due to insufficient time. Therefore, battery charging
behaviors from the charge controller is undetermined. There factor will also
impact the output voltage obtain from both solar and wind controller, as earlier
simulations are conducted at fixed calculated load values.
The simulated results of the inverter tally with the calculated values in the
design stage. However, the only concern here would be finding standard
power transformer part having the required number of turn’s configuration to
keep cost low.
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Critical Review & Reflections
Although project objective is to design an integrated energy converter, I have
learned to tackle the project in a system top down manner. This approach not
only helps me to understand each system blocks functionality but also to have
a clearer picture of what input and output parameters that need consideration
during design phase.
Due to work commitment and having to carry out project work concurrently, it
is critically important to manage time effectively. Hence, Gantt chart and
decision flow chart are created to remind myself of completing the assigned
task within specified time frame and also ensuring project stays on track. In
the beginning, focus points are mainly gathering information on the required
power converter topology and understanding how is operates. As time passes,
new search areas are defined and information grows with it.
If I were to undertake this project again, it would be more feasible to purchase
the student PSIM version immediately. So there is more time for simulation
rather than searching one month for the dull version copy.
5.3
Future Recommendation
In order to have a fully functional system, more simulation test is required to
ensure product safety and reliability, therefore, the following recommendation
for future works.
Wind Controller:

Modeling of wind turbine where its AC output varies over a wide range
of wind speeds. Different wind pattern (Noisy, Ramp, Gusty and etc…)
can then be created to analyze the output voltage response more
accurately.
Lead Acid Battery:

Modeling of lead acid battery to determine its life time, capacity,
impedance and behavior of charging / discharge process.
Charge Controller:

Implement Overcharge & Discharge Protector Hysteresis Cycle
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References
1. http://en.wikipedia.org/wiki/Energy_in_the_United_States
2. Renewable energy resources, 2nd Edition by John Twidell and Tony
Weir
3. http://en.wikipedia.org/wiki/World_energy_resources_and_consumption
4. http://www.electro-tech-online.com/content/theory/
5. http://www.slideshare.net/mareenotmarie/wind-turbine-generator-wtgyawing-and-furling-mechanisms
6. http://www.knmi.nl/samenw/hydra/faq/profile.htm
7. http://www.windmission.dk/workshop/BonusTUrbine.pdf
8. http://www.electronics-tutorials.ws/diode/diode_6.html
9. http://www.icpress.co.uk/etextbook/p276/p276_chap1.pdf
10. http://en.wikipedia.org/wiki/Maximum_power_point_tracker
11. http://www.ee.bgu.ac.il/~pedesign/Graduate_problem_papers/papers
2009/Renewable_Up.pdf
12. http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?arnumber=666033
13. http://www.smpstech.com/mtblog/continuous_ccm_and_discontinuous
_conduction_mode_dcm.html
14. www.convertertechnology.co.uk
15. Modern Wind Turbine Controller Design, by D.A.J. Wouters
16. http://www.freesunpower.com/chargecontrollers.php
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Appendix A – Schematics Diagram
A.1 Solar Controller MPPT Schematics
A.2.1 Wind Controller Non-Inverting Back-Boost Schematics
A.2.2 Boost Compensation Network
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A.2.3 Compensation Network Buck
A.2.4 Buck-Boost Mode Selector
A.3 Charger Controller Schematic
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A.4 Inverter Schematic
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Appendix B – Simulation Plot
A.1 Simulation Plot of PV Array
Figure A.1.1, (I-V Plot) At 800w/m Irradiance Level
Figure A.1.2, (P-V Plot) At 800w/m Irradiance Level
Figure A.1.3, (I-V Plot) At 600w/m Irradiance Level
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Figure A.1.4, (P-V Plot) At 600w/m Irradiance Level
Figure A.1.5, (I-V Plot) At 400w/m Irradiance Level
Figure A.1.6, (P-V Plot) At 400w/m Irradiance Level
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Figure A.1.7, (I-V Plot) At 200w/m Irradiance Level
Figure A.1.8, (P-V Plot) At 200w/m Irradiance Level
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A.2 Simulation Plot of Closed Loop MPPT at Different Irradiance Level
Figure A.2.1, Vout and Vpv Voltage Response at 800w/m2
Figure A.2.2, Vout and Vpv Voltage Response at 600w/m2
Figure A.2.3, Vout and Vpv Voltage Response at 400w/m2
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Figure A.2.4, Vout and Vpv Voltage Response at 200w/m2
Figure A.2.5, Inductor Voltage Response at 800w/m2
Figure A.2.6, Inductor Voltage Response at 600w/m2
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Figure A.2.7, Inductor Voltage Response at 400w/m2
Figure A.2.8, Inductor Voltage Response at 200w/m2
Figure A.2.9, Inductor Current Response at 800w/m2
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Figure A.2.10, Inductor Current Response at 600w/m2
Figure A.2.11, Inductor Current Response at 400w/m2
Figure A.2.12, Inductor Current Response at 200w/m2
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Figure A.2.13, Capacitor Ripple Response at 800w/m2
Figure A.2.14, Capacitor Ripple Response at 600w/m2
Figure A.2.15, Capacitor Ripple Response at 400w/m2
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Figure A.2.16, Capacitor Ripple Response at 200w/m2
Figure A.2.17, Capacitor Current Response at 800w/m2
Figure A.2.18, Capacitor Current Response at 600w/m2
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Figure A.2.19, Capacitor Current Response at 400w/m2
Figure A.2.20, Capacitor Current Response at 200w/m2
Figure A.2.21, Duty Cycle at 800w/m2
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Figure A.2.22, Duty Cycle at 600w/m2
Figure A.2.23, Duty Cycle at 400w/m2
Figure A.2.24, Duty Cycle at 200w/m2
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Figure A.2.25, Ipv and Iout at 800w/m2
Figure A.2.26, Ipv and Iout at 600w/m2
Figure A.2.27, Ipv and Iout at 400w/m2
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Figure A.2.28, Ipv and Iout at 200w/m2
Figure A.2.29, Verror at 800w/m2
Figure A.2.30, Verror at 600w/m2
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Figure A.2.31, Verror at 400w/m2
Figure A.2.32, Verror at 200w/m2
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A.3 Simulation Plot of Wind Controller with Different Voltage Level DC
WTG
Figure A.3.1, Output Voltage Response due to 12Vdc Input
Figure A.3.2, Output Voltage Response due to 24Vdc Input
Figure A.3.3, Output Voltage Response due to 36Vdc Input
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Figure A.3.4, Output Voltage Response due to 48Vdc Input
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Appendix C – Product Specification
C.1 Solar Panel Specification
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C.2 Wind Turbine Specification
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C.3 6V Lead Acid Battery Specification
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Appendix D – PSIM Simulation Software
PSIM is specifically developed for control system, electrical engineering,
dynamic system simulation and power electronics applications. The PSIM
simulation software is developed and market by POVERSIM. PSIM customers
include universities and companies in over 40 countries.
PSIM simulation software will be used throughout this project to analyze the
power converter circuitry behaviors. The key features to why PSIM is popular
in the industry and electronics education worldwide is as follows:
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Circuit components can be set up fast and easy in the circuit schematic
program (PSIM Schematics), due to it friendly user interface
environment.
It provides add-on modules for varies modeling to analog and digital
control system, motor drive system and thermal analysis.
It has a built-in C compiler which allows you to enter your own C code
into PSIM without compiling.
Accurate simulation result is obtained with fast simulation speed.
Able to change components parameters values during simulation and
sees an updated waveform instantly.
PSIM simulation result can be analyzed easily using various postprocessing function from the waveform display program (SIMView).
PSIM is able to link to Mathlab / Simulink for co-simulations.
It allows engineers to determine system/circuit behavior without the
hassle of actually building physical hardware, thus increasing engineer
productivity rate, while reducing development cost and time-to-market.
Limitation on PSIM Demo Version 9.0.1:
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The number of elements in the schematic is limited to 34.
The new devices cannot be added to the database, and chances
cannot be saved.
The number of data points is limited to 6,000.
The C code function disabled.
The many blocks disabled such as the C Script Block, Power Modeling
Block, Embedded Software Block, and General DLL Block.
The Renewable Energy Package disabled.
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