synchronous motors Flashcards
What are the key features of sinusoidal permanent motors?
A rotor with pennanent magnets giving a rotor field of an appropriate number of poles.
The magnets can be surface mounted or interior magnets according to the design.
The magnetic field should have a circumferential distribution which is as close to sinusoidal as possible - the magnets can be shaped to assist with this.
The stator nonnally has a conventional three-phase winding with a pole number matching that o f the rotor.
why do sinusoidal BLDC motors always have the same number of poles in the stator winding as magnetic poles in the rotor, whereas trapezoidal BLDC motors may not
Trapezoidal uses a fixed current switched into any pair of windings
Sine-wave drives work by interaction of nice sine-waves of current and flux, and to obtain a useful torque and smooth performance they must have the same pole numbers
Trapezoidal just depends on waveforms (windings and magnets) with portions aligned, so there is no need for matched pole numbers and theses are explicitly avoided where concentrated windings are used to avoid it locking up magnetically (cogging)
