Electrical
Permanent-Magnet Motor: How the Stator Keeps the Rotor Turning
A rotating magnetic field pulls a permanent-magnet rotor around the shaft
A permanent-magnet motor puts magnets on its rotor and uses stator currents to create torque. In the brushless three-phase version shown here, an electronic controller switches the stator currents in step with rotor position, keeping the field ahead of the magnets so the shaft keeps turning.
- RotorPermanent magnets on the shaft
- StatorStationary copper windings
- DriveThree-phase inverter (illustrated)
- TorqueMagnetic fields interact across the air gap
- ControlCurrent phase tracks rotor position
Interactive visualization
Press play, or step through manually. The visualization is yours to drive — try it before reading on.
Watch the 60-second explainer
A condensed visual walkthrough — narrated, captioned, under a minute.
What is permanent in a permanent-magnet motor?
The rotor carries magnets that provide its magnetic field without an electrical supply to the rotor. A stator surrounds it with coils; when current flows in these windings they create a magnetic field across the air gap. Magnetic interaction tends to align the rotor with the stator field. If the field stays fixed, the rotor eventually aligns and torque falls away. To make a motor, the stator field must keep moving.
This animation depicts one brushless, three-phase topology. Permanent magnets do not by themselves imply brushless construction: brushed permanent-magnet DC motors also exist, with magnets on the stator and a wound rotor. The positions of magnets and coils, and the commutator, matter.
How three-phase commutation makes a rotating field
An inverter applies controlled currents to three sets of stator windings, usually called phases A, B and C. By advancing their current phases in sequence, the controller creates a rotating magnetic field. The colored coil glow in the visualization is a schematic of that switching, not measured current. The arrow indicates a field direction held slightly ahead of the rotor magnet. That angular offset is what sustains torque in this simplified model.
In a real permanent-magnet synchronous motor, electrical angle depends on the number of pole pairs; mechanical and electrical revolutions need not coincide. Control can use Hall sensors, an encoder or sensorless estimation. The purpose of rotor-position feedback is to energize the right phases at the right time, not merely to run a fixed flashing pattern.
Where the turning force comes from
The motor converts electrical power to mechanical power through electromagnetic forces. Current in stator conductors and the rotor's magnetic field interact; the resulting torque acts across the air gap and turns the shaft. If the controller stopped advancing the field, a loaded rotor could settle or stall. If it advances appropriately, the rotor continues to follow. The display's model speed is illustrative and is not a specification for any manufactured motor.
Torque depends on current, magnetic flux, geometry and control angle. A real design must also consider voltage limits, heating, magnetic saturation, mechanical load and cooling. The visualization isolates the commutation idea rather than simulating those coupled effects.
Efficiency does not mean no losses
A brushless permanent-magnet rotor needs no slip rings or brushes to carry excitation current into its magnets. That can remove rotor copper loss and brush wear present in some other designs. But stator windings still heat by electrical resistance. The iron core has hysteresis and eddy-current losses, the inverter dissipates power, and bearings and airflow introduce mechanical losses. Efficiency is therefore design- and operating-point-dependent.
These motors appear in fans, drones, industrial drives and electric vehicles because power density and controllability can be attractive—not because friction or winding losses vanish.
What to watch in the animation
First locate the red and blue poles of the rotor magnet inside the blue stator coil ring. As drive increases, selected coils brighten; the amber arrow marks the commanded stator-field direction, slightly ahead of the rotor. The green ring emphasizes the torque interval. The rotor turns throughout; follow the labels as they highlight magnets, fixed coils, field offset, torque, and timed commutation. Use Back and Next to compare these layers of one continuously operating motor.
This is a teaching model, not an electromagnetic field solver: coil brightness, field direction and model speed are schematic. Its lesson is the causal sequence rotor position → commutated stator current → field offset → torque → rotation.
| Feature | Brushless PM motor (shown) | Brushed PM DC motor | Induction motor |
|---|---|---|---|
| Rotor field | Permanent magnets | Wound rotor energized by brushes | Induced rotor currents |
| Stator field | Driven windings | Permanent magnets | Driven windings |
| Commutation | Electronic inverter | Mechanical brush/commutator | AC supply/inverter establishes rotating field |
| Rotor electrical contacts | Not required | Brushes required | Not required for squirrel-cage rotor |
| Important losses | Stator copper, iron, inverter, bearings | Rotor copper, brush, iron, bearings | Stator and rotor copper, iron, bearings |
Frequently asked questions
What makes a permanent-magnet motor spin?
Stator current creates a magnetic field that exerts torque on the rotor magnets. A controller keeps advancing that field with rotor position instead of letting the rotor settle at alignment.
Is every permanent-magnet motor brushless?
No. The animation shows a brushless motor with magnets on the rotor and windings on the stator. A brushed DC motor can instead have permanent magnets on its stator and a wound rotor with a mechanical commutator.
Why does a brushless motor need rotor-position information?
To keep torque in the intended direction, the inverter must switch phase currents relative to the magnet's position. Hall sensors, encoders or sensorless estimation provide that position information.
Does a permanent-magnet motor have zero electrical losses in the rotor?
The depicted rotor does not need excitation current, but a real motor still has stator copper, core, inverter and mechanical losses. Magnet and rotor losses can also occur under changing fields.
What is the difference between a PMSM and a BLDC motor?
Both can use permanent magnets and electronic commutation. The names commonly distinguish sinusoidal versus trapezoidal drive and back-EMF conventions, but usage varies by manufacturer; the fundamental rotor-and-stator principle is shared.