tracking maximum power point of a multi panel solar...
TRANSCRIPT
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Tracking maximum power point of a
multi panel solar system
Presenters:
Annum Malik
Asad Najeeb
Joveria Baig
Sohaib Iqbal
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Presentation at a glance…
Introduction
Project Overview
PV panel characteristics
Block diagram and flow of project
DC-DC convertor
Charge controller
Q & A session
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Introduction
Need for alternative sources:
a. Fossil fuel depletion
b. Fossil fuel pollution
c. Increase in energy demand
d. Gap in supply and demand
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Why solar power??
Drivers
Continuous source
Environment friendly
Low running cost
Low variability
Challenges
Low efficiency (19%)
High installation cost
only in day light
Market trend
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Why solar power??
Drivers
Continuous source
Environment friendly
Low running cost
Low variability
Challenges
Low efficiency (19%)
High installation cost
only in day light
Market trend
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Go green and save green with clean power!
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Project Overview
Mission Statement:____________
-To operate the solar panel at its
maximum power point under variable
environmental conditions
-To operate a multi panel system at
maximum power point of each panel
-To achieve maximum power efficiency
Problem Targeted
Increased Efficiency______
Maximum
tracking
efficiency up to
more than 89.2%Market trends shifting to cater
demand_______________________
_
Market
moving
towards
Cleaner
energy
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PV array characteristics
Power maxima varies with irradiance and
temperature
MPPT algorithm needed to track this
maxima in varying conditions
To operate each of them at their
maximum power point
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OUR VISION
ELECTRICITY FOR ALL
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PROJECT OVERVIEW
DC-DC
converter
Panel A
Panel B
Charge
ControllerBJT
Excess power
delivered to load
Micro
controller
irradiance temperature
V pv
PWM
DAC
I base
V out
I out
V battery
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Case 1: Not on maximum power point
1. MPPT algorithm detects system is not on MPP.
2. It calculates the optimum voltage the panel should be on.
3. PWM signal is generated to alter the duty cycle, ensuring constant V out .
4. I base is calculated using V optimum . I out is hence changed. ( B * I base )
5. Characteristic resistance changes ( V out / I out ).
6. The load-line hence shifts, and the solar panel starts operating at MPP.
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Case 2: Change in irradiance or temperature
1. Microcontroller detects the change
2. New optimum voltage is calculated.
3. I base calculated accordingly
4. Duty cycle of the PWM wave is altered to ensure V out remains constant.
5. I base changes I out. Hence the load line shifts to intersect with MPP.
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Case 3: Battery is not fully charged i.e. variable load resistance
1. V battery is measured by the micro controller.
2. A PWM is generated to ensure V out = V battery .
3. I base is altered to ensure the load line continues to intersect
with the MPP.
4. As the battery charges, V battery changes dynamically, hence
PWM is continuously altered.
5. I base is also changed dynamically ensuring MPP is maintained.
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Measure G now and T now
Calculate Tcell
Measure V pv and dP / dV
Calculate co-efficients P1-
P4
dP / dV
= 0V optimum = V pv
Duty cycle calculated
dP / dV >
0
V pv = V pv + cV pv = V pv - c
YES
NO
YESNO
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Equations
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Single input buck converter
-Dealing with continuous
conduction mode.
-Input signal from Vd from solar
panel
-Use PWM duty cycle, D, generated
from microcontroller for switching.
-Essentially passing through a 2nd order
low pass filter to get Vo.
-Vo = Vd * D
-Change D continuously to get
constant Vo.
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Single input buck converter (contd.)
-Output current, IL, has a waveform as
shown.
-Output voltage is voltage across
capacitor = Vo + delta(Vo)
-Ripple in output current and output
voltage can be minimized by selecting
corner frequency of low pass filter,
fc << fs , which is our switching
frequency.
-fc = 1 / (2*pi *sqrt(RC))
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TWO INPUT BUCK CONVERTER
Traditional two input buck converter
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A BETTER DESIGN
Cost reduced and power circuit simplified
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TWO FAULTY APPROCHES
Connecting the two sources in parallel and PWM used to
transfer power to the load (based on the time sharing
concept).
Disadvantage : power cannot be delivered to the load
simultaneously.
Connecting the sources in series with bypass paths incase
one of the input is not connected.
Disadvantage: huge variations when only one source is
connected.
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INNOVATIVE DOUBLE INPUT PWM DC-DC
CONVERTER
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ADVANTAGES
Both sources can transfer power individually as well as
simultaneously.
No variations
And the magnitude of the input dc voltage can be higher
or lower than the one with regulated output.
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CIRCUIT OPERATION
MODE1 (SHI: ON/SLO: OFF):
VHI will charge the inductor and the capacitor as well as
provide current to the load.
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MODE2 (SHI: OFF/SLO: ON):
In this mode VLO will charge the inductor and the capacitor
will provide the current to the load
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MODE3 (SHI: OFF/SLO: OFF):
Both the voltage sources are disconnected from the circuit
and thus the energy stored in the inductor and capacitor
will be released to provide the required current to the load.
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MODE4 (SHI: ON/SLO: ON):
The input voltages VOL and VHI are connected in series to
charge the inductor. The capacitor provides the current to
the load.
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OUTPUT WAVEFORMS
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CHARGE CONTROLLER
Regulates the rate at which current is added or drawn
from the battery.
Prevents over charging, over voltage and complete
discharging (by disconnecting the load)
Life of the battery is increased and it is protected from
getting damaged.
“12 volts” solar panels emit around 16 to 20 volts so
charge controllers are vital.
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TYPES OF CHARGE CONTROLLERS
SERIES CONTROLLERS: disables further current flow
when batteries are fully charged.
SHUNT CONTROLLERS: diverts excess current to drive
the shunt load such as a water heater.
Simple charge controllers stop charging a battery when
they exceed a set high voltage level, and re-enable
charging when battery voltage drops back below that
level.
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PWM CONTROLLERS
Good quality controllers use PWM to charge.
On reaching the regulation voltage (14.1V), a PWM
algorithm reduces the charging current and continues
charging slow enough to prevent the battery overcharging
instead of stopping charging and so are 30 % more
efficient.
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3 STAGES OF A SINGLE CHARGE CYCLE
BULK PHASE: voltage of the battery gradually rises to a
bulk level while drawing maximum current (14.4 to 14.6
volts).
ABSORPTION PHASE: voltage is maintained at the bulk
level for some specific time while the current tapers off
gradually as the battery charges up.
FLOAT LEVEL: After the absorption time passes, the
voltage is lowered to a lower level i.e. the float level (13.4
to 13.7 volts) during which a small maintenance current
flows until the next cycle.
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