Advantages of DC series
• Huge starting torque
• Simple Construction
• Designing is easy
• Maintenance is easy
• Cost effective
Permanent Magnet DC Motor
• Higher efficiency since no electrical energy is used or losses
incurred for developing or maintaining the motor’s magnetic
• Higher torque and power density.
• Linear torque speed charcteristics. that are more predictable.
• Better dynamic performance due to higher magnetic flux
density in air gap.
• Simplified construction and essentially maintenance-free.
• More compact size.
simple torque and speed control without
General Torque Equation
Translational (linear) motion:
F : Force (Nm)
M : Mass (Kg )
v : velocity (m/s)
T : Torque (Nm)
J : Moment of Inertia (Kgm2 )
: angular velocity ( rad/s )
• Above a certain size, synchronous motors are
not self-starting motors. This property is due
to the inertia of the rotor; it cannot instantly
follow the rotation of the magnetic field of the
• synchronous motor produces no inherent
average torque at standstill, it cannot
accelerate to synchronous speed without
some supplemental mechanism.
• Synchronous motors are especially useful in applications
requiring precise speed and/or position control.
• Speed is independent of the load over the operating range
of the motor.
• Speed and position may be accurately controlled using
open loop controls, e.g. stepper motors.
• Low-power applications include positioning machines,
where high precision is required, and robot actuators.
• They will hold their position when a DC current is applied to
both the stator and the rotor windings.
• Increased efficiency in low-speed applications (e.g. ball
• Asynchronous motor
• AC electric motor
• Three-phase induction motors are the most
common and frequently encountered
machines in industry
• The electric current in the rotor needed to
produce torque is induced by electromagnetic
induction from the magnetic field of the stator
• Does not require mechanical commutation
– simple design, rugged, low-price, easy maintenance
– wide range of power ratings: fractional horsepower to
– run essentially as constant speed from no-load to full
– Its speed depends on the frequency of the power
• not easy to have variable speed control
• requires a variable-frequency power-electronic drive for
optimal speed control
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