Lecture 1: Basic Concept of DC Choppers(DC to DC Converters) : Principle of Operation & Applications 

Basic Concept of DC Choppers(DC to DC Converters) : Principle of Operation & Applications :
Topics :
Introduction to Choppers
AC link Chopper and DC chopper
Definition & Principle of operation of DC chopper
General Features of DC choppers
Functions of DC choppers
Applications of DC choppers
Types of DC choppers
Chopper is a device which converts fixed DC voltage to variable DC voltage
Systems that perform better with variable DC voltage source
Subway car
Trolley buses
Battery operated vehicle
Battery chargers
The conversion of fixed DC voltage to variable DC voltage is done by :
AC link Chopper
DC Chopper
AC Link Chopper :
First DC is converted to AC by inverter ⇛ AC is stepped up/stepped down by Transformer ⇛ which is then converted back to DC by Diode rectifier
DC Chopper :
It is static device which converts fixed DC voltage to variable DC voltage directly in single stage.
It is static device which converts fixed DC voltage to variable DC voltage directly in single stage.
Principle of Chopper Operation :
Power devices has ON state voltage drop of 0.5V to 2.5V across them.
Power devices are represented by switch SW with arrow.
SW is ON ⇒ Current flows in direction of arrow
SW is OFF ⇒ C No current flows.
Functions of DC choppers
To convert DC input voltage to DC output voltage.
To regulate DC output voltage against load and line variations.
To reduce AC voltage ripple on DC output voltage below required level.
To provide isolation between the input source and load.
To protect the supply system and source from Electro magnetic interference.
General Features of DC choppers
DC choppers are designed using power BJT, POWER MOSFET,GTO or forced commutated thyristor as semiconductor switch.
They can provide smooth acceleration control to motors
DC choppers are highly efficient
Fast dynamic response
They can offer regenerative breaking of DC motor, resulting in energy saving.
Applications of DC choppers
Transport Systems
Traction motor control in electric automobiles
Trolley cars
Marine hoists
Forklift trucks
Mine haulers
Used in DC voltage regulators
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