Table of contents
1.
Project overview
2.
Project milestones
3.
Research
4.
PV panel
5.
Ultracapacitor
6.
Buck converter
7.
Challenge
8.
References
Project Overview:
Standalone photovoltaic systems are
common in remote areas away from the
national grid. A typical standalone system incorporates a photovoltaic panel,
regulator, energy storage system, and load. Principally the Valve Regulated Lead
Acid (VRLA) battery is employed for energy storage, because
of its low cost and
wide availability.
High starting current is required by applications that involve star
t
ing motors. The
starting current required can be 6
–
10 times the normal operating current of the
motor. Normally the peak current is supplied by the
battery. The battery must
have large capacity to account for the increased current discharge, even though
the current surge might only need to be met for a few seconds at a particular
time. It is a well known fact that a large currnet decreases the state
of charge
(SOC) of the battery much faster than a smaller current over a longer period.
The ultracapacitor has a greater power density than the battery, allowing the
ultracapacitor to provide more power over a short
er
period of time. Conversely,
the batt
ery has a higher energy density compared to the ultracapacitor to supply
the base load. The main objective of this project is to invertigate the role of the
ultarcampacitor in energy storage systems that have peak load requirements. A
dc

dc converter will
be designed, built and tested to allow a small battery to
charge up an ultrcapacitor. The whole system will be modeled in
MATLAB/Simulink
Project Milestones:
Review of solar Panel
structure

The charact
eristic of solar panel
.

Analysis of MPPT in
solar
energy and how to apply this to recharge a
battery.

Electrical characteristics and equivalent circuits of
solar cell.
Review of Ultrcapacitors

Physical construction and operation of ultrcapacitors

Application of ultracapacitors in energy storage for auto
motives and
renewable energy sytems

Electrical characteristics and equivalent circuits of ultracapacitors
DC

DC Converter

Select and design a dc

dc converter to charge the ultrcapacitor from a
small 12 V battery (size the battery for the application)

Sele
ct a dc motor with high starting current for the application

Simulate the converter in PSICE

Use MATLAB/Simulink to model the complete system
Demonstrate the application with the battery, ultracapacitor, dc

dc converter
and motor

Identify the parameters
that would be important in optimising the
overall system

Build and test the complete system
Pass
Investigate the role of ultrcapacitors in energy storage systems

Review the power and energy requirements of an ultrcapacitor in an
application such as a motor
with high starting current.

Design a DC/DC converter to charge the ultracapacitor from a battery

Provide SPICE simulation results including models for suitable circuit
components
Average
Build and test a DC/DC solution for charging the ultrcapacitor

Use
a 12 V battery (this will require a small battery charger)

Determine the efficiency of the converter over all load conditions and
identify the main loss contributors

Test the system with a motor load that has high starting current.
Good
Provide a Simulink
/MATLAB model of the complete system

Model the battery, motor and ultrcap

Optimise the power conversion circuitry to provide maximum power
from the battery to the ultracapacitor to the load
Very good

Demonstration of a complete system in operation
Excel
lent
Identification of the optimisation parameters and a prodedure to carry out
such an
optimization
RESEARCH
Ultracapacitor technology has been commercially available for over the past
decade. They can store much more
energy than conventional capacito
rs
.
They
can be discharged o
r charged faster
and can
deli
ver
more than 10
times
more powe
r
than batteries
. Also,
ultracapacitors typically
have 10
times
lower
charge time when compared to lead acid batteries.
They also offer 10

100
times the energy densit
y
of conventional capacitors.
Therefore i
n terms of energy and power
density, ultracapacitors can
be placed
between
batteries a
nd conventional capacitors
. A comparison of
conventional
storage t
echnologies is shown
below.
Conventional
capacitor
Lead Acid
Battery
Ultracapacitor
Specific
energy
density
<0.1
10

100
1

10
S
pecific power
density
<100,000
<1,000
<10,000
C
ycle life
>500,000
1,000
>500,000
C
harge/discharge
efficiency
>95%
70

85%
85

98%
F
ast charge time
1ms

0.001ms
1

5hrs
0.3

30sec
D
ischarge t
ime
1ms

0.001ms
0.3

3hr
0.3

30sec
The
application
of ultracapacitors is
very
useful
in
the
hybrid
storage system
.
Ultracapacitors can be used to provide the short bursts of
energy needed by
high
starting current motor
. Ultracapacitors do not need regul
ar replacement
like
batteries because they are not as adversely affected
during repetitive deep
charging and discharging. This also
implies that ultracapacitors are more
environmentally
friendly since they don’t need to be frequently discarded.
In this p
roject, I will deal with the progress from the PV panel to the load by
ultracapacitor. Here is simple flow chart for it.
PV
panel
(MODEL:SANYO HIP210

NKHB5
)
A solar cell basically is a p

n semiconductor junction.
When exposed to light, a
current proport
ional to solar
irradiance is
generated. The circuit model of PV cell
is
il
l
ustrated
.
Most
of the generated current flows through diode
w
hen
V=0
. Rs and Rsh
represent small losses due to the connections and leakage respectively. There is
very little cha
nge in Voc for most instances of load current. However,
when
a load
is connected to
V
then the load current draws current away from the diode. As
the load current increases, more current is diverted away from the diode.
I

V characteristic as shown in the f
igure below.
Maximum Power Point Tracking
Maximum Power Point Tracking, frequently referred to as MPPT, is an electronic
system
that operates the Photovoltaic (PV) modules in a manner that allows the
modules to produce all
the power they are capable of
. MPPT is not a mechanical
tracking system that “physically moves”
the modules to make them point more
directly at the sun. MPPT is a fully electronic system that
varies the electrical
operating point of the modules so that the modules are able to deliver
maximum
available power. Additional power harvested from the modules is then made
available as
increased battery charge current. MPPT can be used in conjunction
with a mechanical tracking
system, but the two systems are completely different.
Ultrac
apacitor
The equivalent circuit used for conventional capacitors
can also be applied to
ultracapacitors. The circuit schematic
below
represents the first

order model for
an
ultracapacitor. It’s comprised of four ideal circuit elements:
a capacitance C, a
series resistor Rs, a parallel resistor Rp,
and a ser
ies inductor L. Rs is called
ESR
(
equivalent series
resistance
) and contributes to energy loss during capacitor
charging and discharging. Rp simulates energy loss
due to capacitor self

discharge, and is o
ften referred to as
the leakage current resistance. Inductor L
results primarily
from the physical construction of the capacitor and is usually
small. However, in many applications, it can’
t be neglecte
d
particularly those
operating at high frequencies
or
subjected to hard switching.
In this project,
RC parallel branch model
(circuit below)
will be used
.
Each RC branch has a different time constant. The fast

term branch dominates
the charge and discharge behavior in the order of a few seconds. The medi
um

term branch dominates the behavior over the scale of minutes. Finally the slow

term branch governs the long

term charge and discharge characteristics.
RC parallel branch model reflects the internal charge distribution process very
well.
This model has
G
ood response of the ultracap’s dynamic behavior during
charging and discharging.
Accuracy is better
then first

order model.
Buck converter(
DC/DC converter
)
Circuit model below is buck convert
er by pspice.
This DC/DC converter is co
nnection between 12V battery and Ultracapacitor.
From the equation in buck converter,
diL/dt=(Vs

Vo)/L
when
switch
is
on

(1)
diL/dt=(

Vo)/L
s=0
when
switch
is
off

(2)
assume switch=s , and combine equation (1) and (2)
diL/dt=(SVs

Vo)/Lo

(3)
Here is value for simulation in simulink.
Input voltage Vin=12V
Output voltage Vout=2.7*3=8.1V
Variation input voltage=+9¬15V
R=10
ohm
L=0.3m
H
C=0.2m
F
Frequency=100khz

> T=1/100k=0.01
D=Vout/Vin=8.1/12=0.675
Vout is 3 of 2.7V ultracapacitors connecte
d in series. The designed model below
is by equation(3).
Challenge
1.
Design DC/DC converter with Ultracapacitor model.

DC/DC converter model in the paper is not practical when ultracapacitor
is connected. I will design DC/DC converter with
RC pa
rallel branch model
including values.
2.
Decide a motor
required high starting current and connect it with
ultracapacitor model.

Motor should be decided to get each efficient value such as
inductor,capacitor and resistance.
3.
Simulate a Simulink/MATLA
B model of the complete system.
REFERENCE
http://en.wikipedia.org/wiki/Electric_double

layer_capacitor
http://www.maxwell.com/ultracapacitors/index.asp
http://powerelectronics.com/mag/power_ultracapacitor_technology_powers/
http://www.solargy.com.sg/pdtsvc.php?subcat=HSPVP&pid=HIP

210
http://www.ieee.org
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