Differences Between The Permanent Magnet Motor And Asynchronous
Motor:
01. Rotor Structure
Asynchronous motor: The rotor consists of an iron core and a
winding, mainly squirrel-cage and wire-wound rotors. A
squirrel-cage rotor is cast with aluminum bars. The magnetic field
of the aluminum bar cutting the stator drives the rotor.
PMSM Motor: The permanent magnets are embedded in the rotor
magnetic poles, and are driven to rotate by the rotating magnetic
field generated in the stator according to the principle of
magnetic poles of the same phase attracting different repulsion.
02. Efficiency
Asynchronous motors: Need to absorb current from the grid
excitation, resulting in a certain amount of energy loss, motor
reactive current, and low power factor.
PMSM Motor: The magnetic field is provided by permanent magnets,
the rotor does not need exciting current, and the motor efficiency
is improved.
03. Volume And Weight
The use of high-performance permanent magnet materials makes the
air gap magnetic field of permanent magnet synchronous motors
larger than that of asynchronous motors. The size and weight are
reduced compared to asynchronous motors. It will be one or two
frame sizes lower than asynchronous motors.
04. Motor Starting Current
Asynchronous motor: It is directly started by power frequency
electricity, and the starting current is large, which can reach 5
to 7 times the rated current, which has a great impact on the power
grid in an instant. The large starting current causes the leakage
resistance voltage drop of the stator winding to increase, and the
starting torque is small so heavy-duty starting cannot be achieved.
Even if the inverter is used, it can only start within the rated
output current range.
PMSM Motor: It is driven by a dedicated controller, which lacks the
rated output requirements of the reducer. The actual starting
current is small, the current is gradually increased according to
the load, and the starting torque is large.
05. Power Factor
Asynchronous motors have a low power factor, they must absorb a
large amount of reactive current from the power grid, the large
starting current of asynchronous motors will cause a short-term
impact on the power grid, and long-term use will cause certain
damage to the power grid equipment and transformers. It is
necessary to add power compensation units and perform reactive
power compensation to ensure the quality of the power grid and
increase the cost of equipment use.
There is no induced current in the rotor of the permanent magnet
synchronous motor, and the power factor of the motor is high, which
improves the quality factor of the power grid and eliminates the
need to install a compensator.
06. Maintenance
Asynchronous motor + reducer structure will generate vibration,
heat, high failure rate, large lubricant consumption, and high
manual maintenance cost; it will cause certain downtime losses.
The three-phase Permanent magnet synchronous motor drives the
equipment directly. Because the reducer is eliminated, the motor
output speed is low, mechanical noise is low, mechanical vibration
is small, and the failure rate is low. The entire drive system is
almost maintenance-free.
The three-phase Permanent magnet synchronous motor drives the
equipment directly. Because the reducer is eliminated, the motor
output speed is low, mechanical noise is low, mechanical vibration
is small, and the failure rate is low. The entire drive system is
almost maintenance-free.
