Induction Motor vs Synchronous Motor│ Difference between Synchronous and Inducti HD

Most pumps and fans operating in industrial and commercial applications are currently driven by AC induction motors. “ACIM”, which stands for “alternating current induction motor”, is an asynchronous type of motor that relies on electric current to turn the rotor. Torque is produced by electric current in the rotor. The electric current is generated through electromagnetic induction from the magnetic field of the stator windings. In an ACIM, the rotor always rotates at a lower speed than the magnetic field. A “PMSM”, which stands for “permanent magnet synchronous motor”, relies on magnets to turn the rotor, which spins at the same speed as the PMSM’s internal rotating magnetic field.

There are a few key differences between AC induction Motors and Permanent Magnet Synchronous Motors.

Permanent magnet motors MUST operate with a drive.

AC induction motors can be used without a VFD to drive a pump or fan, but are often installed with variable frequency drives (VFD) in pump systems or fan systems in an effort to improve system efficiency. Permanent magnet synchronous motors require a drive to operate. PMSMs cannot run without a drive. A VFD is required to precisely control the speed of the PMSM to meet the application requirements for pressure, flow, volume, etc. Some new VFDs already come with permanent magnet motor control options as a standard feature, allowing operators to control the permanent magnet motor to drive the fan and/or pump more efficiently.

Permanent magnet motors offer significant efficiency improvements over AC Induction Motors.

A permanent magnet motor’s full load efficiency is higher than an AC induction motor. Figure 1 below shows the ranges of efficiencies between two standards of AC Induction Motors and known published Permanent Magnet Motors.

Figure 1. PM motor efficiencies on VFD power. ACIM on Sine wave. ACIM motors lose .5 – 1.5 points of efficiency when run on VFD.