DC DRIVES VS AC DRIVES

· DC drives:

Advantage in control unit
Disadvantage in motor

· AC Drives:

Advantage in motor
Disadvantage in control unit

· Torque Equation: Motor drives
· Torque Equation: Graphical
· Load Torque

· 4Q OPERATION
· 4Q OPERATION: LIFT SYSTEM
· DC MOTOR DRIVES
· Equivalent circuit of DC motor
· Torque-speed characteristics
· DC Motor Speed Control
· Speed control of DC Motors

· Methods of Armature Voltage Control
· Converters For DC motor Drives
Switch–mode converters: 1Q Converter
Switch–mode converters: 2Q Converter
Switch–mode converters: 4Q Converter

DC DRIVES:

Electric drives that use DC motors as the prime movers

DC motor:

Industry workhorse for decades
Dominates variable speed applications before PE converters were introduced

Will AC drive replaces DC drive ?

Predicted 30 years ago
DC strong presence – easy control – huge numbers
AC will eventually replace DC – at a slow rate

Advantage:

simple torque and speed control without sophisticated electronics

Limitations:

Regular Maintenance
Expensive motor
Heavy motor
Sparking

General Torque Equation

Translational (linear) motion:

F : Force (Nm)
M : Mass (Kg )
v : velocity (m/s)

Rotational motion:

T : Torque (Nm)
J : Moment of Inertia (Kgm2 )
w : angular velocity ( rad/s )

Drive accelerates or decelerates depending on whether Te is greater or less than TL
During acceleration, motor must supply not onlythe load torque but also dynamic torque, ( Jdw/dt ).
During deceleration, the dynamic torque, ( Jdw/dt ), has a negative sign. Therefore, it assists the motor
torque, Te.