Battery Charge Regulator for a photovoltaic power system using microcontroller

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Battery Charge Regulator for a photovoltaic power
system using microcontroller

• By
• Raed Wael Ennab Raja Saed Anabtawi

Supervised by Prof. Marwan Mahmoud
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Introduction

• Since the beginning of the oil crises, which
  remarkably influenced power development programs
  all over the world, massive technological and
  research efforts are being concentrated in the
  field of renewable energy resources. In the solar
  sector for electricity generation, greater
  attention is being given to photovoltaic
  conversion.

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Features

• 1- Charge any rechargeable battery 12V, 24V.
• 2- Supply any low dc load.
• 3- Solar-powered.
• 4- Displays charging status.
• 5- Polarity checking.
• 6- Current Limiting.

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Advantages and Disadvantages

• The advantages are
• 1- Renewable resource.
• 2-
  Silent.
• 3- Non-polluting.
• 4-
  Little maintenance.
• 5- easy to install.
• 6-
  Reliability.
• And the disadvantages are
• 1- Very expensive. 2- No work at
  night.

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Block Diagram
Solar Panel
Regulator
PIC
Load
Lead Acid battery
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Photovoltaic cells
Regulator
Solar Panel
PIC
Load
Battery

• In our design, the solar panels will function
  as a power supply to our circuit. It will
  convert the sun radiation to voltage and current.
• types of photovoltaic cells
• 1-mono-crystal silicon.
• 2-Polycrystal silicon .
• 3-Amorphous silicon (thin film silicon).

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efficiency
Material level of efficiency in production
Mono crystalline silicon 14-17
Polycrystalline silicon 13-15
Amorphous silicon 5-7
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number of cells

• The output voltage of a module depends on the
  number of cells connected in series. The module
  we used was 25 cell connected in series.

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solar cell I-V characteristics
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A Typical Current-Voltage Curve for a Module at
(1000)W/m2 (500)W/m2
A Typical Current-Voltage Curve for a Module at (85)c and (25)
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Photovoltaic Arrays
Series connection
Parallel connection
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Charge Regulator
Regulator

• The solar charge regulator main task is to charge
  the battery and to protect it from overcharging
  and deep discharging. Deep discharging could
  also damage the battery.

Kind of charge regulators 1-Simplest switch
on/off regulators. 2-PWM ( Pulse Width
Modulation). 3-MPPT charge regulator (Maximum
Power Point Tracking).
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Regulator
Solar panel
PIC
Load
Lead Acid Battery
Lead acid Battery

• 1- We are going to work on six-cell lead-acid
  batteries.
• 2- Voltage/cell 1.75-2.4 V.
• 3- Battery charge.
• 4- Battery efficiency.
• 5- Minimum Voltage.

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Lead acid battery

• In our project, the circuit we built has two
  leds red one and green one.

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Circuitry
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circuitry

• S
• S

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Circuitry

• when the voltage is lower than 14.4 V the
  comparator (IC3) allows a high negative output
  signal to switch on the PNP transistor (Q1).
• During charging, the battery voltage increase
  until it reaches the 14.4 V value. At this
  voltage, the transistor (Q1) will be switched
  off.
• N1 and N2 from the IC4001 are utilized as pulse
  oscillators for the purpose of testing.
• In this short period, transistor Q2 will be
  switched on, and a current will flow from the
  emitter to the collector of Q2.

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• Then the comparator (IC2) compares the battery
  voltage with the open-circuit voltage of the
  solar generator.
• The main objective of using the pulse generator
  is to control the voltage of both the solar
  generator and the battery continuously.
• The objective of the comparator (IC5) is to
  control the battery voltage during the
  discharging mode

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two MOSFET transistors were utilized instead of
one

• - To make the prevention of the battery
  discharging via the solar generator as strong as
  possible.
• - The temperature of the two transistors, due to
  the voltage drop across them, is divided equally
  between them.
• - Increasing the reliability of the controller
  since one transistor can perform the task of the
  other in case of its failure.
• - This arrangement protects the controller from
  failure whether it is connected to the solar
  generator first or to battery.

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Features of The Locally developed Battery Control
Unit (BCU)

• - Protects battery against overcharging the unit
  controls the charging current via a regulated
  impulse, thus preventing harmful overcharging.
• - Protect the battery against deep discharging
  the unit controls battery discharge by means of
  bistable load relay.
• - If the battery charge drops bellow a
  predetermined voltage threshold, the relay
  automatically disconnects the load, this is
  indicated by a red light- emitting diode (LED).
• - The unit is protected against battery reverse
  polarity via a diode (D4).

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PIC
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Flow chart
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• Here we used the DAC to convert the digital
  output from the PIC to Analog.

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Results
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Results
Voltage (V) Current (mA) Resistance (ohm)
0 401.7 0
1.92 384 10
3.85 379.2 20
5.12 370.1 30
6.02 365 40
6.9 360.3 50
7.5 353.5 60
8.61 352.2 70
10.4 351.4 80
11.3 350.8 90
15.4 305 100
19.1 0 gtgt

I-V Characteristic
At G950 w/m2
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Results

• Fill factor and efficiency
• The Imp 350 m A and the Vmp 15 volt
• So the max power point 15.350 5.25 watt.
• The fill Factor
• FF (ImpVmp)/ (Is.cVo.c)
• (150.350)/ (19.4) 70
• The efficiency
• Eff P.opt/ A.Ee
• Eff5.25/ 0.30.3950 6.1

All calculations are at G950 w/m2
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• The results we got were

Ibatt (mA) Vbatt (V) Ipv (mA) Vpv (V)
323 12.6 328 17.1
296 12.9 302 14.9
289.6 13.01 298 14.1
270 13.27 275 13.46
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Problems we have faced

• 1- The output voltage was about 15 volts, and the
  PIC accept only 5 V maximum.
• 2- The radiation from the sun was different from
  day to another.
• 3- The wires we used first were the thin wires so
  when the current passed these wires got hotter.

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The applications for our project
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Conclusion and Recommendation

• -From the technical and economical viewpoints, it
  can be said that the PV technology has attained
  an acceptable degree of operational efficiency
  and reliability.
• -Module degradation seemed to be a problem in
  amorphous PV technology.
• -The tested amorphous PV module showed power
  degradation between 16.4 and 39 at the end of
  the first year testing period.
• -if we have more time we could program the PIC
  with a program that can drive a stepper motor and
  rotate it as the max radiation from sun
  and that by using photo sensors.

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