Have read somewhere, that brushless DC motors have constant torque.
How can this be true?
Regard motor on the picture:
If constant current flows as red arrows indicate, the magnetic field appears as blue arrows indicate. The permanent magnet (not shown) tends to put it's N and S poles appropriate.
All this time, the current remains constant.
Then how the torque can be constant, as the magnet approaches it's final position? Isn't torque decreasing as this happening?
Wouldn't it be more constant torque, if I power the winding coils with three phase sinusoidal current, having phase ahead by some value relative to rotor?
Best Answer
Perhaps you have misunderstood the working principle of BLDC and PMSM. The working principle is similar to DC motor. We hava an armature current and excitation current (or permanent magnet), it is important that you undarstand that both magnetic fields are right angle, as the torque between two fileds are T=T_max*sin(phi).
IN BLDC is the same, the magnet never aproaches to final angle, because the stator is switched, so that there is always almost right angle - the same is for DC, there is a brush commutator.