A Comparison Study of the Commutation Methods for the Three-phase Permanent Magnet Brushless Dc Motor

The three-phase permanent magnet brushless dc (BLDC) motor inherently needs an electronic commutation circuit to drive it because it is not a self-commutating motor. It is contrary to the conventional brush motor which commutates itself. This paper presents a comparison study of three widely used different commutation methods in terms of the complexity of the commutation circuit, torque ripple, and efficiency. The principle of the operation of the three-phase BLDC motor is introduced first and then three commutation strategies – trapezoidal (sixstep), sinusoidal and field oriented control (FOC) are discussed in detail. The characteristics of the three commutation methods are investigated intensely, and the advantages and disadvantages of each are compared to the others. The second generation MC73110 motor control chip from Performance Motion Devices, Inc. is used for experimental verification of three different commutation strategies. It makes possible to control the BLDC motor with trapezoidal commutation with Hall-effect position sensor. The sinusoidal commutation with encoder position feedback and the FOC with either Hall or encoder position feedback signal are also achievable. The experimental motor waveforms and torque ripples with different commutation methods are further investigated.