Smart Battery Charger with Input Unity Power Factor

Under The Guidance of:-

Dr. A.K. Kapoor Dr. R Mahanty

Smart battery charger Group no. 6• Anjani Kulani (06000439)• Devansh Arpit (06000440)• Abhishek Verma (06000441)• Vivek Ranjan Gavendra

(06000443)• Ravinder Kumar (06000444)• Ankit Kumar (06000446)• Harihar Prasad (06000447)

Aim : Design a Smart Battery Charger circuit with the following specifications.

Input voltage :230V acBattery voltage : 12V dcInput Power Factor :UnityBattery Used : Lead Acid BatteryMOSFET Rating: 400V dcMOSFET Gate Pulse : 15V dcIGBTGate Pulse: 12V dcIGBT ON state Voltage Drop: 1.2V

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Battery charger- A battery charger is a device used to thrust energy into a secondary cell by

forcing an electric current through it.

Need of battery charger –Electrical vehicles, inverters and UPS systems.

Chemical process during charging & discharging - Lead, lead oxides & acids

converts into electrons, water & lead sulphates & in charging reverse process takes place.

Basic Terminologies

Charging rates - slow charge,quick charge, fast chargeCharge termination Charge efficiencyAmp-hour

Basic charging methods

Constant voltageConstant current

Pulsed charge Float charge

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Types of batteries:

Nickel-cadmium battery (NiCd)Lithium ion battery

Rechargeable alkaline batterySodium sulphar batteries

Lead-acid battery

Advantages of lead acid battery :Wide operating temperature range

Safer operationLong service life

Types of battery charger:SimpleTrickle

Timer basedSmartFast

PulseInductive

USB basedSolar chargers

Smart Battery Charger

A smart battery charger always monitoring the battery's voltage.it is having a comparator & a

controller circuit which compares the terminal voltage of the battery with a certain specified value. Charging is

terminated when the battery is fully charged.

Block diagram

Smart battery charger circuit

A battery charger consist of a rectifier circuit, boost power factor converter & a

buck converter in cascade.

Rectifier circuit is used here to convert the AC voltage into the DC voltage.

Boost power factor converter improves the input power factor (nearly 1).

A Buck converter is used here to step down the dc voltage as required by the battery.

Rectifier Circuit and it’s Output

The Main Purpose of Boost Converter is to Control the Input Power Factor.

The Parameters of Boost Converter are set so as to Regulate the Input Power Factor close to Unity.

Switching Frequency = 50Hz (equal to Input Frequency)

D(Duty Cycle) = 0.5

Switching has been implemented through MOSFET.

Boost PFC Converter

Boost PFC Converter

Input Voltage And Current In Phase

Input PF = 1

Buck Converter

Output voltage of buck converter

Buck Converter has been used to Step Down the Voltage required to charge the battery.

The Voltage assumes a constant value of nearly 12 V for charging the Battery at 0.5sec.

Comparator Circuit

The Comparator Circuit has been used to Sense the Battery Voltage and send therequired signal to the Controller which Switches ON or OFF the IGBT switch andhence stop the charging process when the battery is fully charged.

A comparator is a circuit that compare a signal voltage applied at one input of an opamp with a known

reference voltage at the other input.”It is basically an open loop op-amp with output Vsat (=Vcc).

Two types of comparator:

1.Non-inverting comparator 2.Inverting comparator

The comparator has two possible outputs:1) -Vsat if Vapplied < Vref 2) +Vsat if Vapplied > Vref

This output is then fed to the IGBT switch connected in the charging path. As long as output is +Vsat (if Vapplied > Vref) the IGBT is “on “ and otherwise it is “off”. The time during which the IGBT is on the voltage of battery rises and the current falls. When the voltage reaches to the required limit, the voltage across the charging resistor falls below Vref , The IGBT turns off and further charging

is stopped.

Process of charging

The output of Buck converter is applied to the battery through a charging circuit that consists of a charging resistor and an IGBT driven by the control circuitry

discussed above. As long as the positive pulse is available to the IGBT, the circuit feeds charging current

to the battery. This current through the battery develops a voltage across the resistor of charging

circuit. This voltage is compared with the reference voltage.

Schematic: The orCAD simulation of the simple charging circuit is shown below where a battery

is replaced by a capacitor.

Advantages of Smart Battery Charger

Provides distinctive advantages in system safety, performance and total cost.

Various applications of smart battery charger• Cellular phones.•Video cameras

• Laptops .