Pm Ac Synchronous Motor

[subrao]

now a days pm ac syn. motors are increasingly used and replacing induction motors.

 

i have some difficulty in understanding how the motor is started.

a conventional synchronous motor is started with the help of damper windings or by driving it with an external

motor and exciting the field winding when it attains near synchronous speed. How such thing can be achieved

in case of a pm motor as field is permanently produced and there are no damper windings . even damper windings are

provided with field on it will not start.

 

subrao

[marke]

Hello Subrao

 

Permanent Magnet AC motors are usually controlled by a special inverter.

Some VFDs have a PM mode to enable them to be used with a PM motor.

 

With and inverter controller, the motor is started by reducing the frequency down to zero then increasing the frequency up to the desired speed.

 

Best regards,

Mark.

[shartah]

now a days pm ac syn. motors are increasingly used and replacing induction motors.

 

i have some difficulty in understanding how the motor is started.

a conventional synchronous motor is started with the help of damper windings or by driving it with an external

motor and exciting the field winding when it attains near synchronous speed. How such thing can be achieved

in case of a pm motor as field is permanently produced and there are no damper windings . even damper windings are

provided with field on it will not start.

 

subrao

 

 

 

Hello subrao

As we know that pm ac synchronous motor's rotor consists of permanent magnets, the principle used for operation is just the repulsion and attraction property of magnets.

The motor is run by a Variable Frequency Drive (VFD) which supplies current to the stator electro magnets such as to create a repulsive force or attractive force on rotor permanent magnets such that torque is produced and the motor starts to rotate. The motor is fitted with an encoder for getting feed back on rotor pole position identification (North pole or South pole), position feed back and speed feed back from which the VFD will control the PM synchronous motor through electronic commutation.

Hope you got answer for your quistion

 

Regards

Sharath