Strength of BLDC (EC) motor with sinusoidal commutation

Is a EC motor with sinusoidal commutation stronger?

The difficulty answering this question is to find and to define reasonable references. We restrict us here on current and torque considerations.

Block commutation

Remarks:

• Motor data in the catalog are given for block commutation.
• The reference current of the block commutation is the value of the block current in each commutation intervall I_B.
• Due to the torque ripple, only the average torque is considered.
• Hence, the torque constant of block commutation k_M,B gives the average torque per I_B.

Sinusoidal commutation

Definitions:

• The current reference with sinusoidal commutation is defined as the amplitude of the sinusoidal phase current I_S.
• The torque shows no ripple with sinusoidal commutation. No averaging is needed.
• The torque constant of the sinusoidal commutation k_M,S is defined as the ratio of the produced torque and the reference current I_S.

The following formulas and graphics are also present by the attached file "Sinus-versus-Block-Commutation_English.pdf":

Results for sinusoidal commutation:

1. Max. continuous current is about 15% higher with sinusoidal commutation.
2. Torque constant is about 10% smaller with sinusoidal commutation.
3. Max. continuous torque is about 5% higher with sinusoidal commutation.
4. Hence, the continuous operation range is enlarged by about 5%.

See also the attachments SinusBlockkommutierung.PDF (german) and SineCommutationMMC.PDF (english) (with information about space vector control) below.

Remark for flat motors at standstill

In flat motors operated with sinusoidal commutation at stand still (e.g. in a positioning system with EPOS controller), one phase winding can overheat due to the special arrangement of the winding. Therefore, the continuous current limitation of the controller should be set to 85% of the motors rated current.