In this blog post, we will discuss Permanent Magnet Motors referred to as PMAC motors. This type of electric motor is designed to be more efficient than its cousin the AC induction motor. They boast a perfect power factor at any speed range!
PMAC motors have many other features that make it a great choice for a myriad of applications. It has the ability to produce more torque per ampere than an AC induction motor. PMAC motors can also be smaller and lighter than a comparable AC induction motor. This type motor is very quiet and can be used in applications where noise needs to be minimized.
In PMACs, magnets mounted on or embedded in the rotor couple with the motor’s current-induced, internal magnetic fields generated by electrical input to the stator. More specifically, the rotor itself contains permanent magnets, which are either surface-mounted to the rotor lamination stack or embedded within the rotor laminations. As in common ac induction motors, electrical power is supplied through the stator windings.
Permanent magnet motors are categorized as “magnetically-coupled motors”. This is a term that describes the use of magnetism to produce torque in a motor. PMACs have no mechanical commutator. They rely on magnetic attraction and repulsion for electrical switching without any sparking or arcing at contact points.
PMAC-compatible drives (known as PM drives) substitute the more traditional trapezoidal waveform’s flat tops with a sinusoidal waveform that matches a PMAC motor’s back EMF more closely. This way torque output is smoother. These motor-drive setups can be operated as open-loop systems in midrange performance applications requiring speed and torque control. Here, PMAC motors are placed under vector-type control.
Speed of PMAC Motors
With these motors, speed is a function of frequency — the same as it is with induction motors. But, PMAC motors rotate at the same speed as the magnetic field produced by the stator windings; it is a synchronous machine. So, if the field is rotating at 1,800 rpm, the rotor also turns at 1,800 rpm — and the higher the input frequency from the drive, the faster the motor rotates.
They are suitable for variable or constant-torque applications, where the drive and application parameters dictate to the motor how much torque to produce at any given speed. This flexibility also makes PMACs suitable for variable-speed operation requiring ultra-high motor efficiency.
PMAC motors are very energy-efficient. Permanent magnet motors, operate within a wide range of electrical input frequencies. They easily respond to changes in frequency or torque demand. This makes them an attractive solution for high power density per unit volume, variable speed applications. (such as wind turbines, electric cars and more).