Permanent magnet synchronous motors (PM motors) fed by inverter are applied to industrial applications where variable-speed drive with constant torque and high efficiency are required as in compressors, conveyor belts, etc.

The use of the PM motor is increasing in applications where smooth torque, low vibration and noise levels are required as in elevators.

In addition, it is very useful in applications where saving space and eliminating the gearbox are essential, because it can operate self-ventilated on a wide speed range.

The main features of PM motors are high efficiency, reduced size, high torque performance and wide speed range.

PM motors with high energy magnets (NdFeB) in the rotor, in contrast with conventional squirrel cage induction motors, have less Joule losses in the rotor. As Joule losses (RI2) account for a significant portion of total losses in induction motors, replacing squirrel cage by magnets, the PM motor ensures much higher efficiency than the squirrel cage and meets the requirements for the EFF1 and EFF2 standard.

Magnets in the rotor guarantee a great reduction of electric losses and consequently a lower temperature rise of the motor. Due to these advantages, the volume and weight of a PM motor compared to the same power induction motor is reduced and its lifetime is significantly increased.

Compared with an equivalent induction motor, the volume of the PM motor is reduced to roughly 47percent, resulting in a higher torque/volume ratio and a reduced weight by as much as 36percent.

The PM motor is at least one frame size smaller than the induction motor and in some cases it can be two frame sizes lower.

Reducing the frame size the cooling system is consequently reduced for the same torque/power ratio, thus a significant reduction of noise caused by the fan coupled to the motor shaft is possible.

A special CFW09VFD manufactured by WEG is necessary with particular software to drive the PM motor. The vector control technology can be utilised to drive the PM motor from zero speed up to the field weakening region.

The VFD requires continuous position signal to maintain an accurate synchronisation of the excitation waveforms with the rotor angular position at every time.

However, it is necessary a high resolution rotor position sensor. Nowadays this control could be implemented using a sensorless technology which is available due to advanced control algorithms.

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WEG Equipamentos Elétricos SA is based in Jaraguá do Sul, Brazil. www.weg.net