Synchronous and Asynchronous Motors

Etymologically speaking in a synchronous motor, the rotors rotate at a speed similar to the speed of a magnetic field, or stator field, while asynchronous motors have the rotor running at a slightly slower speed than that of the induced magnetic field.
Asynchronous motor (above) vs Synchronous (below)

Synchronous motor Asynchronous motor (induction)
More power at the same speed No brushes, i use the electromagnetic induction faraday. The rotor is made by laminated pieces, to dissipate eddy currents caused by changes in B and also hysteresis loss in ferromagnetic materials
ω=kf, so the rotational speed is always k times the input frequency Cheap and made by few parts, so reliable as well
Windings on both stator and rotor Presence of slip: the 2 rotating field are asynchronous
Easy to control and smooth functioning Squirrel cage into the rotor, connected only in the ends. No rotor windings
More complex in building Current in stator creates a B in stator who induces I into rotor and the consequently B over there. The motion is the consequence of the interaction of the 2 magnetic fields
More unitary power (pay attention to the heat dissipation) and performance η The cost is 2-3 times higher


  • It is very rare that the constructor of an asynchronous gives a lot of characteristics;
  • It is difficult that, in an asynchronous, the characteristics are quite flat at low speed, torque and current would not be however so much proportional
  • The fact that there is talk of an external inductance: if there are no magnets, the external inductance does not make sense (at least, not for the weakening, if involved): in the asynchronous there is no a magnet to be contrasted, just lower the “fluxing”, so you only have a sort of L · i, to lower it;
  • If you notice a “no load current” curve, which rises only in defluxing (it starts to rise a little after the “base” speed, that is the one at which we start to deflux), that current only serves to counteract the flow of the magnet. If there were not the magnet would not need to increase it, and probably in an asynchronous there would also be at low speed.
  • Assembling stator core with thin laminated silicon content steel reduces magnetic / iron losses. Adding silicon with steel reduces Hysteresis loss and assembling with laminated steel reduces Eddy Current loss.

i would like to share some of experiences of motor lamination manufacturing: the process of the stator and rotor lamination process as below:

  • Cut the raw material silicon steel sheets(electrical steel) to a strip for cutting, this normally use professinal cutting machine to do it because the raw material from silicon steel factory is large dimension
  • If you just need prototype, EDM Wire cutting or laser cutting the sheets to the shape you designed per drawing requirement; EDM wire cutting has better tolerances
  • If you need mass production, then a stampig mold tooling should be desinged to punch the sheets; a progressive die stamping with interlock has been proved to have highest production efficiency, while it will cause more eddy current losses due to abnormal magnetic field in the interlock point area
  • After the silicon steel sheets has been punched or cut, then we need to do the lamination; a fixture should be designed to promise the tolerances and normally there is some typical lamination technology: A. Bolt screw; B: Tig Welding; C Laser Welding; D: Bonding. due to stator bonding lamination do not have any welding or interlock point, so it can decrease the eddy iron loss at lowest level and engineers can get highest motor efficiency
  • Normally after the stator lamination completed, you will do the slots insulation with plastic overmold injection, epoxy powder coating or use insulation paper when you do winding process
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