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Motor solution selection and newbie questions

Mohammed Lokhandwala
Intellectual 700 points

Other Parts Discussed in Thread: MSP430F5324, LAUNCHXL-F28027F, BOOSTXL-DRV8301, INSTASPIN-BLDC, DRV8313, CONTROLSUITE, DRV8308, DRV8303

I have this list of questions. I want to run a simple sensorless out-runner BLDC motor from Hobbyking. It's rated at 200W and 25000 RPM just to give a sense of the parameters. I am not using it for RC application however I want the following. The motor can be thought to have a load attached to it at all times and the load would change as the motor moves it.

a. Rapid start times with minimum delay. 

b. Forward and reverse commutation.

c. Breaking.

1. Approximately what is the expected time a typical motor can be expected to start spinning using sensor-less operation? I understand it will differ based on motor parameters but I just want a sense of this value to determine if sensor-less is an option or not for us.

2. Is there any library or code that is available for MSP430 based devices for BLDC commutation even if it is not as advanced as Instaspin? We are already using MSP430F5324 MCU with a normal PMDC motor but want to switch to brushless BLDC.

3. Is Instaspin the only TI provided library for BLDC communation? Is there any open source library for any MCU including Piccolo or MSP that is commonly used.

4. Can Instaspin-FOC (not motion) perform forward, reverse and breaking action?

5. Can Instaspin-FOC provide RPM feedback to user program.

6. Can Instaspin-FOC software encoder be used instead of an optical encoder for position tracking and rotation counting? Forward, Backward.

7. Can the LAUNCHXL-F28027F be used as an ISP with a  custom board ?
 
8. Can the BOOSTXL-DRV8301 design support higher AMP motors by simply replacing the MOSFETs? Thus can we use it as a reference design ?
 
9. Why does DVR8301/2 have only 2 but not 3 Current Sense Amps! 

 Thanks!

  • 0
    TI__Guru** 119680 points

    Mohammed Lokhandwala said:
    I want to run a simple sensorless out-runner BLDC motor from Hobbyking. It's rated at 200W and 25000 RPM just to give a sense of the parameters

    The quality of control you can get with our software control solutions will be dependent on the amount of flux (more is better) and the amound of inductance (more is better).  Some of the hobby motors run really well with solutions like InstaSPIN-FOC but some (the higher Kv) have such low inductance, high RoverL, and large Isc (torque ripple) that you can't really get good enough currrent measurements all the time, so highest speeds become challenging and very low speed becomes challenging.

    Mohammed Lokhandwala said:
    1. Approximately what is the expected time a typical motor can be expected to start spinning using sensor-less operation? I understand it will differ based on motor parameters but I just want a sense of this value to determine if sensor-less is an option or not for us

    The command can happen nearly instantaneously. How fast it can accelerate is a factor of the motor construction and parameters. There are things to consider regarding knowing alignment of the rotor initially, especially if load is nearing maximum.

    Mohammed Lokhandwala said:

    2. Is there any library or code that is available for MSP430 based devices for BLDC commutation even if it is not as advanced as Instaspin? We are already using MSP430F5324 MCU with a normal PMDC motor but want to switch to brushless BLDC.

    The DRV8313 EVM includes an MSP430 device that is running a verion of InstaSPIN-BLDC.  There are several "community" driven Bemf zero crossing and hall based solutions as well. May want to try 430ohm.com  There isn't anything from TI that I'm aware of, motor control just isn't a focus for the MSP430 business.

    Mohammed Lokhandwala said:

    3. Is Instaspin the only TI provided library for BLDC communation? Is there any open source library for any MCU including Piccolo or MSP that is commonly used.

    No, there is a hall based and Bemf ZC based solution provide in controlSUITE. There is an example for both on the DRV8312-C2-KIT

    Mohammed Lokhandwala said:

    4. Can Instaspin-FOC (not motion) perform forward, reverse and breaking action?

    absolutely

    Mohammed Lokhandwala said:

    5. Can Instaspin-FOC provide RPM feedback to user program.

    absolutely

    Mohammed Lokhandwala said:

    6. Can Instaspin-FOC software encoder be used instead of an optical encoder for position tracking and rotation counting? Forward, Backward.

    No. The FAST software observer is very accurate once the rotor is moving enough to provide feedback signals. But it breaks down near 0 speed. It is only mean to be used in torque/velocity applications, not position control.  We do have a sensorless algorithm that can track rotor position even at 0 and near 0 speed, but it requires the motor to have special construction (high saliency).

    Mohammed Lokhandwala said:
    7. Can the LAUNCHXL-F28027F be used as an ISP with a  custom board ?

    I'm not sure what ISP means, but if you're asking if you can build your own inverter and just plug-in a LaunchPad, sure.

    Mohammed Lokhandwala said:
    8. Can the BOOSTXL-DRV8301 design support higher AMP motors by simply replacing the MOSFETs? Thus can we use it as a reference design ?

    Not as is. If you increase amperage (or total power) you will probably need more area to dissipate heat. This design is good for about 250W, so if you need to increase voltage, decrease max current. If you need to increase current, decrease voltage.

    Mohammed Lokhandwala said:
    9. Why does DVR8301/2 have only 2 but not 3 Current Sense Amps! 

    Many control solutions only use a single total current or two shunts (and calculate the 3rd from U+V+W=0).  We like to have the option of the 3rd so that we can run in over-modulation, always able to get a good sample at any measurement time.  If you don't need to use over-modulation you don't need the 3rd sample.

    There is a new DRV83x device coming out with 3 sense amps though....

     

  • 0 in reply to ChrisClearman
    Intellectual 700 points

    ChrisClearman said:

    1. Approximately what is the expected time a typical motor can be expected to start spinning using sensor-less operation? I understand it will differ based on motor parameters but I just want a sense of this value to determine if sensor-less is an option or not for us

    The command can happen nearly instantaneously. How fast it can accelerate is a factor of the motor construction and parameters. There are things to consider regarding knowing alignment of the rotor initially, especially if load is nearing maximum.

    [/quote]

    What I was looking for here is the typical time InstaSpin-FoC would take to determine the rotor position before it started the the commutation logic. Can you give any indication like 10ms or 100ms or 500ms.

    ChrisClearman said:

    7. Can the LAUNCHXL-F28027F be used as an ISP with a  custom board ?

    I'm not sure what ISP means, but if you're asking if you can build your own inverter and just plug-in a LaunchPad, sure.

    [/quote]

    I meant using it as In System Programmer and debugger for our custom design.

  • 0 in reply to Mohammed Lokhandwala
    TI__Guru** 119680 points

    Mohammed Lokhandwala said:

    What I was looking for here is the typical time InstaSpin-FoC would take to determine the rotor position before it started the the commutation logic. Can you give any indication like 10ms or 100ms or 500ms.

    InstaSPIN-FOC does not determine the rotor position before it starts.  It can start the PWM commands instantly and start driving the rotor. As soon as there is almost any rotor motion FAST will lock on in < 1 electrical cycle and allow you to drive the rotor into a higher speed. 

    We will be relasing some initial position detection algorithms that work with InstaSPIN-FOC in the future.  I believe these are takign about 100ms on most test motors today.

    Mohammed Lokhandwala said:

    I meant using it as In System Programmer and debugger for our custom design.

    Yes, you can wire out the signals as a way to create a very cheap JTAG debugger. Or just purchase a cheap XDS100v2 JTAG debugger.

     

     

  • 0 in reply to ChrisClearman
    Intellectual 700 points

    ChrisClearman said:

    The DRV8313 EVM includes an MSP430 device that is running a verion of InstaSPIN-BLDC.  There are several "community" driven Bemf zero crossing and hall based solutions as well. May want to try 430ohm.com  There isn't anything from TI that I'm aware of, motor control just isn't a focus for the MSP430 business.

    Hi, I don't see the 430ohm.com site. I tried .org and .net but no luck. Could you confirm the URL? Also I could not find the InstaSPIN-BLDC implementation in the software download of the DRV8313 EVM page, any help getting to it would also be appreciated.

  • 0 in reply to ChrisClearman
    Intellectual 700 points

    Thanks! but ...

    1.

    http://www.ti.com/tool/drv8313evm I could find easily, its the source code I cannot find.

    2. What is the advantage of over-modulation? What aspect of motor control does it improve ? (torque or RPM or something else like faster position detection etc)

     

  • 0 in reply to Mohammed Lokhandwala
    TI__Guru** 119680 points

    1. on that page there is a zip download

    Board Files and Software: DRV8313 EVM (Rev. C)

    2. over-modulation is a feature for sine-wave / space vector modulation solutions to move into over-modulation and essentially turn into a 6-step trapezoidal controller, while still doing FOC. It only moves into this modulation if you enable it AND if the extra voltage for this modulation is required to create the speed being requested.  We have found that our over-modulation technique actually gets slightly higher average voltage to the motor so we can run just a bit faster than a standard 6-step controller.

     

  • 0 in reply to ChrisClearman
    Intellectual 700 points

    What is the role of current sensing in InstaSPIN - FOC? Does FAST need current data or only BEMF ? What would happen if we dropped all the current sensing circuit? Is the whole current sensing bit for protection or does it get used in the commutation logic?

  • 0 in reply to Mohammed Lokhandwala
    Intellectual 700 points

    What is the meaning of this statement?

    (2) During states where the phase is driven with a PWM signal, using asynchronous rectification, the LS gate is held off (L); using synchronous rectification, the LS gate is driven with the inverse of the HS gate.

     

    From http://www.ti.com/product/DRV8308/datasheet/detailed_description#SLVSCF79635

  • 0 in reply to Mohammed Lokhandwala
    TI__Guru** 119680 points

    current sensing is required.

    we are doing field oriented control, which requires knowledge of the motor currents so that a location of the rotor may be estimated and an appropriate current vector be created in the stator oriented correctly to the rotor flux angle.

     

    please ask your DRV8303 question on the Applications - Motor Drivers forum.