![]() Sinusoidal motors come under a number of names, including PMSM (permanent magnet synchronous motor), an AC servo motor, or BLAC (brushless AC, a term used byĪtmel). In a sinusoidal motor, current travels through all three windings at any point, while in a trapezoidal motor, current only flows through 2 of the 3 windings. For this reason trapezoidal motors are very common. Sinusoidal motors have lower torque ripple (less vibration, mechanical stress e.t.c e.t.c), but suffers from higher switching losses and greater drive complexity than a trapezoidal motor. One is to produce a trapezoidal shaped BEMF, the other produces a sinusoidal shapes BEMF. There are two standard ways of winding the coils. So it pays to get the right motor for the right job! Trapezoidal vs. Therefore, the BLDC motor and trapezoidal(six-step) commutation and the PMSM and sinusoidal commutation are the most desirable combination to produce minimum torque ripple. ![]() The simulation results verify that mismatch of the back-EMF waveform and commutation method produces ripple rich torque. As quoted by Shiyoung Lee, Ph.D., A COMPARISON STUDY OF THE COMMUTATION METHODS FOR THE THREE-PHASE PERMANENT MAGNET BRUSHLESS DC MOTOR), The motor windings can be wound to either give trapezoidal or sinusoidal feedback, which relates to the control methods mentioned further down on this page. Ripple torque is mainly due to fluctuations in the field distribution. Ripple torque is the torque produces by the interaction between the stator and rotor MMF. The 3 phases of a BLDC motor are usually labelled either A, B, C or U, V and W.Ĭogging torque is due to the variation in airgap permanence or reluctance of the stator teeth and slots above the magnets as the motor rotates. Note that if the motor has more than 1 pole pair, you cannot orientate the motor to a known mechanical position without some type of feedback (hall-effect, encoder). If the motors datasheet instead states the number of poles, this is just 2x num. Typical BLDC motors have a number of pole pairs varying from 1 to 5. The number of pole pairs is equal to the number of electrical revolutions per mechanical revolution. The lower the inductance, the higher the PWM needed to the same current ripple. The winding inductance has the useful property of limiting the rate of change of current through the motor, and is what allows you to use PWM to produce smooth current. Winding Inductance: High precision motors typically have lower inductance. ![]() High performance motors can have a time constant as low as 1ms to speed up to 30,000rpm!
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