Progress Report

coalitionhihatElectronics - Devices

Oct 7, 2013 (3 years and 10 months ago)

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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