This document discusses a separately excited DC motor that is controlled using a DC chopper. It describes the components and operating modes of the system. The DC chopper converts a fixed DC input voltage to a variable output voltage, which is used to power the separately excited DC motor. The chopper and motor combination has three operating modes - motoring, regenerative braking, and dynamic braking. The chopper allows for efficient speed control of the separately excited DC motor.
1. DC CHOPPER FED SEPARATELY EXCITED MOTOR:
SUBMITTED BY
S.RAJA RAJESHWARI (14F40)
M.S.SATISH (14F49)
V.DEEPAKKUMAR (14F61)
2. CHOPPERS:
• Chopper is basically a static power electronics device which converts fixed dc voltage / power
to variable dc voltage or power.
• It is nothing but a high speed switch which connects and disconnects the load from source at a
high rate to get variable or chopped voltage at the output
• Chopper can increase or decrease the dc voltage level at its opposite side.
3. DC CHOPPER:
• A DC chopper is a static device that converts fixed dc input voltage to a variable dc
output voltage directly.
• A chopper can be said as dc equivalent of an ac transformer as they behave in an
identical manner.
• This kind of choppers are more efficient as they involve one stage conversion.
• Just like a transformer, a chopper can be used to step up or step down the fixed dc
output voltage.
• Choppers are used in many applications all over the world inside various electronic
equipments.
• A chopper system has a high efficiency, fast response and a smooth control
4. SEPARATELY EXCITED DC MOTOR:
• Separately excited dc motor has field coils similar to that of shunt wound dc motor,
here the field is supplied from a constant voltage so that the field current is constant.
• Usually, in other DC motors, the field coil and the armature coil both are energized
from a single source. The field of them does not need any separate excitation.
• But, in separately excited DC motor, separate supply Provided for excitation of both
field coil and armature coil.
5. 3 MODES OF OPERATION:
There are three modes of operation of the DC chopper used in a separately
excited motor:
• Motoring
• Regenerative braking
• Dynamic braking
14. DYNAMIC BRAKING:
• In this method of braking, the motor which is at a running condition is
disconnected from the source and connected across a resistor.
• When the motor is disconnected from the source ,the rotor keeps rotating
due to inertia and works as a self-excited generator.
• When the motor works as a self-excited generator ,the flow of current and
torque reverses.
• During braking, to maintain the steady torque, sectional resistances are
cut one by one.
15. APPLICATIONS :
• Used in speed control of the separately
excited dc motor
• Offers smooth control ,high efficiency and fast
response.
• Used to step down or step up the fixed dc
input voltage.
