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DRV10970: Question about the BLDC

Eric Li
Prodigy 80 points
Part Number: DRV10970
Other Parts Discussed in Thread: MOTORSTUDIO, MCF8316A, MCF8315C, MCF8329A, MCF8315A

Tool/software:

Hi all,

I am looking for answers to the following questions: 

  • Absence of sensored FOC and sensored sinusoidal product:

The featured integrated BLDC drivers shown in TI.com only provide sensored trapezoidal products. Even the sensored sinusoidal product DRV10970  is available now but it seems that the sensored FOC and sensored sinusoidal is less competitive compared with sensored trapezoidal products. I wonder which reason leads to it.

  • FOC: Improving acoustic performance with automatic dead time compensation:

Table 3-1 in the attachment indicates that FOC control improves acoustic performance with automatic dead time compensation. I wonder if it benefits from the additional control of automatic dead time compensation, or just the nature benefit of FOC.

  • How sinusoidal control determine the angle of three phase references:

Compared with other methods: Trapezoidal control use the truth table to know switch states of FETs after gaining the information form Hall sensor. FOC control determine the angle of references through complex calculation based on the angle of rotor, the current loop and speed loop. However, I have no idea about how sinusoidal control determine the angle. Whether it simply follows the angle of the rotor or have additional calculations to meet the control requirements?

  • 0
    TI__Expert 6660 points

    Hi Eric,

    • Absence of sensored FOC and sensored sinusoidal product:

    Sensored Trapezoidal needs 3 HALL sensors to find rotor position and commutate. 

    Sensored Sinusoidal commutation is based on U Phase and hence only one HALL element is sufficient. The commutation is done every 180 degree by detecting HALL state.

    FOC need three phase BEMF information as precisely as possible. From three phase BEMF data position and speed is extracted and with this information stator windings are excited to maintain 90 degrees torque all the time.  Hence three Hall sensor which can provide BEMF sinusoidal way is preferred, the common HALL sensors in the market are digital which changes state. Nowadays we get analog Hall sensor as well.  

    • FOC: Improving acoustic performance with automatic dead time compensation:

    Because FOC modulates current continuously unlike in other every 180 degree, the harmonic content is managed to compensate for the dead time effect.

    • How sinusoidal control determine the angle of three phase references:

    I explained this for 1st question, commutation is based on the BEMF zero cross detection method, the better the accuracy the better is torque which ensure BEMF is well aligned with Phase current. In sensorless DRV10x has good current sense accuracy and also there is provision for lead angle adjustment for the user to tune to get good performance.

    Thanks and Best Regards,

    Venkatadri S

  • 0 in reply to Venkatadri Shantaram84961
    TI__Prodigy 80 points

    Thank you for your detailed response, but I still need your help to resolve my remaining confusion.

    • Absence of sensored FOC and sensored sinusoidal product:

    It seems that Sensored Sinusoidal commutation need less HALL sensors. So why sensored Sinusoidal products are less in number than sensorless. In contrast, the sensored trapezoidal products are no less than sensorless.

    • How sinusoidal control determine the angle of three phase references:

    Could you share more information about “there is provision for lead angle adjustment for the user to tune to get good performance.”

    Best Regards

    Eric Li

  • 0 in reply to Eric Li
    TI__Expert 6660 points

    Hi Eric,

    Primary advantage of Sensor based commutation helps for position control, low speed (near zero) control and useful for the applications which needs to be controlled at low speed. Sensor-less need minimum speed up to which closed loop control not possible due to poor BEMF. Applications which need low speed high torque are with sensor based

    Lead angle provision is provided to adjust the BEMF and Phase current alignment. Maximum torque for applied current is based on how well BEMF and Current are aligned. For motors without saliency (means Inductance torque is uniform in all 360 degree) BEMF and Phase current phase shift has to be ideally zero which is the maximum torque point and for the non-salient pole motors (Motor inductance varies due to magnet geometry, LD is not equal to LQ) a particular phase shift between BEMF and current helps to utilize reluctance torque.  

    When you test your motor measure the phase current for given speed, vary the lead angle and for certain values current improves and for certain value it degrades and also motor may stall. This effect is due to either increasing / optimizing the torque or reducing the torque and increasing the magnetizing current.

    Thanks and Best Regards,

    Venkatadri S

  • 0 in reply to Venkatadri Shantaram84961
    TI__Prodigy 80 points

    Hi Venkatadri S,

    Thanks for your response.

    It seems that the first paragraph in your response is for my first question and the second and the last one is for my second question, right?

    Based on your first paragraph, I guess that there is no need to use FOC control for the applications which needs to be controlled at low speed (sensor based  commutation). Because in that case the advantage of FOC and sinusoidal is less useful compared to trapezoidal. Therefore, there is no product that combined the sensor and FOC control.

    My second question is addressed well by your response. And could the test to vary the lead angle be achieved by motorstudio?

    Best regards,

    Eric 

  • +1 in reply to Eric Li
    TI__Expert 6660 points

    Hi Eric,

    Motor studio today supports, MCF8316A, MCF8316C, MCF8315A, MCF8315C, MCF8329A, all FOC devices. Future releases will be planned for MCT831x, MCT8329 devices.

    MCF831x do not support lead angle as they are meant for non salient motors where LD = LQ, MCF8329A device provides Flux weakening mode and Lead Angle in Voltage mode operation (similar to DRV10x which are voltage mode controllers).

    MCT831x, MCT8329 has lead angle which are not supported on Motor studio today.

    Thanks and Warm Regards

    Venkatadri S

  • 0 in reply to Venkatadri Shantaram84961
    TI__Prodigy 80 points

    Hi Venkatadri S,

    I have a question about sensorless BLDC.  

    In addition to BEMF, it seems that magnetic linkage can also be used to determine the rotor position, and do we have products that use the latter one? Why we mainly use BEMF for our products?  

    Best regards,

    Eric 

  • +1 in reply to Eric Li
    TI__Expert 6660 points

    Hi Eric,

    Can we start this on new thread.  I will reply to you by this week.

    Thanks and Warm Regards

    Venkatadri S

  • 0 in reply to Eric Li
    TI__Expert 6660 points

    Hi Eric,

    Are you referring to analog HALL sensor, the output of hall varies sinusoidal way?

    Thanks and Warm Regards

    Venkatadri S

  • 0 in reply to Venkatadri Shantaram84961
    TI__Prodigy 80 points

    Hi Venkatadri,

    Thank you for your reply.

    Not refer to analog HALL sensor. It is a solution without sensor, just like the BEMF method to know the position of rotor. Have you ever heard it before? I give more detailed description in the new thread. You can give me answer in the new link.DRV10970: Question about sensorless BLDC - Motor drivers forum - Motor drivers - TI E2E support forums

    Best regards,

    Eric