Transcript Final Presentation

To develop a small scale solar powered
system that will power a DC load, which
incorporates power management
techniques, DC-DC conversion and a
user interface.
Renewable energy source
 Non-polluting
 Reliable
 Can work anywhere sun is shining
 No major mechanical parts
 Relatively no maintenance
 Noise Free
 Last decades

Solar
Panel
DC-DC Converter
Controller
Load
Back-up
Battery
Silicon cells combined in series or parallel
 Converts solar energy into electricity
 Cell Technologies

› Copper Indium Selenide (CIS) and
Amorphous
› Monocrystalline and Polycrystalline

Current varies with cell size and light
intensity
Ip
Rs
Id
Iph
D
Rp
Vo
I  I ph  I d  I p
  q V  I . Rs    V  I .R

s
 n. K .Tcell . Ns 
I  I ph  I sat . e
 1  o


Rp


I ph
S
 I scref .
.[1   Isc (Tcell  Tref )]
Sref



Peak Power of
10 Watts
Vmpp = 15.6 V
Impp = 0.64 A


Voc = 22.9 V
Isc = 0.77 A
The solar panel was tested with
different resistances under a
constant light source
Shell ST10
+
V
-
I-V Characteristic of Shell ST10
5
4.5
4
Current (milli amps)
3.5
3
2.5
2
1.5
1
0.5
0
0
2
4
6
Voltage (volts)
8
10
12
P-V Characteristic of Solar Panel
25
6.7
Power (milli Watts)
20
15
10
5
0
0
2
4
6
Voltage (Volts)
8
10
12
Two MPPT algorithms were considered:
 Incremental Conductance Method
› By comparing incremental conductance
with instantaneous conductance.

Perturb & Observe Method
› By periodically perturbing the PV array
voltage and comparing the output power
with that of the previous cycle. The
operating point oscillates around the MPP
since the system is continuously perturbed.
Algorithm was
implemented using
LabVIEW
 Solar panel read via a
NI-USB 6009
 The voltage was
measured across a
high power resistor to
read current
 Duty cycle output on
NI USB 6009 digital
output line
Start

Set Duty Out
Read V, I
P_new = V*I
P_new > P_old
P_old  P_new
Duty = Duty(+)
Duty =
Duty(-)

Used to implement P&O algorithm
› ‘G’ programming

Also used to generate a user interface
through the front panel
› Waveforms showing voltage and current of
solar panel
› Numeric indicator showing power
› Duty cycle displayed
› ‘Stop’ button to end program




Data acquisition tool
Read data in, and
generate digital
signals out
Does not have a
hardware counter,
cannot generate
digital outputs at
high frequencies
Solution M series

DC-DC converter needed for two
reasons
› To implement the MPPT algorithm
› To bring the DC voltage to an acceptable
level to power the load

Buck converter was chosen and
designed
The most important components are the
inductor and capacitor
 Use Vo = DVi to deduce ideal duty cycle
range (0.3 – 0.5)
 Using both of these values for D, and the
ΔI equation two values for the inductor
were calculated (2.8 mH & 1.6 mH)
 Using the ΔV equation the capacitor
value was determined (21.3 μF)

2.2 mH
+
+
D
Vin
-
PWM
22 uF
L
O
A
D
-
Solar panels only generate power when
there sun available
 Storage element is recommended
 Various rechargeable battery cell
chemistries

› Lead Acid
› Nickel-Cadmium
› Nickel-Metal-Hydride
› Lithium Ion
Up to 99% efficiencies
 Highest weight to energy ratio
 Average voltage of one Li-ion cell is 3.63.7 Volts
 A Li-ion battery pack with a capacity of
4 AH would be enough to store all
energy generated on the longest day of
the year at maximum power
 Safety issues




Overvoltage
Over discharging can
cause short circuit
Battery packs usually
include protective
circuit
› Limits input voltage
› Limits discharge
voltage

Li-ion charger IC is
recommended to
implement charging
profile





Initially it was thought a mobile phone
charging algorithm would have to
implemented
Research showed that the charging
algorithm is employed on the phone
To prove this, a commercial Nokia car
cigarette lighter charger was disassembled
A ‘ma34063a’ DC-DC converter was found
To charge a mobile an appropriate
constant voltage is needed, along with
some circuitry protection





Solar cell equivalent circuit, characteristics
and various cell technologies
Maximum power point tracking techniques
LabVIEW – ‘G’ programming and user
interface
DC-DC converter design including choosing
appropriate components and simulation in
Pspice
Rechargeable Batteries