A permanent magnet (PM) motor is an AC motor that utilizes magnets either embedded within the surface of the rotor or attached to it. PM motors can be categorized into two main structures: interior and surface, each with its subcategories. In the case of a surface PM motor, magnets can be positioned on or inset into the surface of the rotor, enhancing the durability of the motor's design. On the other hand, the positioning and design of magnets in an interior permanent magnet (IPM) motor can exhibit significant variation. The magnets in an IPM motor can be inset as a large block or staggered as they approach the core, while another approach involves embedding them in a spoke pattern.
An induction motor, also referred to as an asynchronous motor, is a widely used AC electric motor. It operates by utilizing electromagnetic induction from the rotating magnetic field of the stator winding to induce the electrical current required in the rotor for generating torque. The rotor of an induction motor can be either a squirrel cage rotor or a wound type rotor.
In this motor, the flux emanating from the stator interacts with the short-circuited coil within the rotor. As per Faraday's law of electromagnetic induction, the presence of the magnetic field induces a current flow in the rotor coil. The rotor coils, being short-circuited, allow the current to circulate through them. Consequently, the current flow within the rotor coils triggers the creation of another magnetic flux within the rotor.
Now there are two fluxes, one is stator flux, and another is rotor flux. The rotor flux will be lagging concerning the stator flux. Because of that, the rotor will feel a torque which will make the rotor rotate in the direction of the rotating magnetic field. This is the working principle of both single and three-phase induction motors.
Induction motors operate based on the fundamental principle of electromagnetic induction. They consist of stationary windings, known as the stator, that generate a magnetic field. This rotating magnetic field induces currents in the rotor windings, leading to the generation of torque necessary for motor function.
On the other hand, permanent magnet motors utilize permanent magnets, often composed of materials like neodymium, to establish a steady magnetic field. This fixed magnetic field interacts with the currents in the rotor windings, resulting in the production of the required torque to drive the motor.
Construction:
Induction motors are comprised of a stator equipped with three-phase windings, along with a rotor that can either be of the squirrel cage or wound rotor type. On the other hand, permanent magnet motors share a stator configuration with induction motors, but their rotor incorporates permanent magnets instead.
Efficiency:
Permanent magnet motors exhibit high efficiency since they lack the rotor losses typically found in induction motors, including losses from rotor copper and rotor iron. On the other hand, induction motors tend to have comparatively lower efficiency due to losses occurring in their rotor windings.