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  1. #1
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    BLDC controller stuck at load condition

    Hi friends,
    We are designing 3 phase inverter for a long while. Our controller works fine at no load condition when a load attached the controller stucks.

    Motor specification:
    -500w motor
    -500rpm
    -13amp rated current

    At no load condition..... Works good
    - current 1.9amps
    - 400rpm
    At load condition.... Works bad
    - current goes above 20 amps
    - 150 to 200 kg load
    - Mosfet dies at this condition ( gate to source shorts )

    About controller....
    - 1kwatts 48v 40amps
    - open loop bldc controller
    - waveform and rise time,fall time of our controllers images, I will update it.

    Is my controller not effectivr to provide a high torque??
    Guide my friends, thankyou in advance.

    - - - Updated - - -

    Waveforms
    Motors back emf.... with 120 degree phase-shift

    Click image for larger version. 

Name:	back emf.png 
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ID:	151657

    [ATTACH=CONFIG]151650][/ATTACH]

    Phase to phase with pwm [10Khz] waveform....

    Click image for larger version. 

Name:	phase to phase voltage with pwm.jpg 
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Size:	144.7 KB 
ID:	151658

    Attachment 151651

    phase to phase voltage without applying pwm....

    Click image for larger version. 

Name:	phase to phase without applying pwm.jpg 
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ID:	151659

    Attachment 151652

    Timings
    Rise time tr= 100ns -200ns
    Fall time tf = 50ns - 100ns

    BLdc controller design
    Feedback is only hall sensor state to drive the phase winding according to the position
    Click image for larger version. 

Name:	Block Diagram for a Brushless DC Motor.png 
Views:	3 
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ID:	151653

    commutation sequence
    clockwise...
    Click image for larger version. 

Name:	CommutationTable_CW.png 
Views:	2 
Size:	76.7 KB 
ID:	151654
    Last edited by BradtheRad; 11th March 2019 at 08:23. Reason: Put images for attachments

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  2. #2
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    Re: BLDC controller stuck at load condition

    Your switching system needs to do the same thing as the commutator in a brushed DC motor. The commutator does what it does automatically, because the forces of magnetic attraction pull the armature around to send juice through the next winding.

    Steps:
    1) A winding contacts the two brushes.
    2) Current flows in the winding.
    3) This creates magnetic force which pulls it toward a nearby opposite pole (magnet or energized coil).
    4) Armature turns a fraction of a turn.
    5) Winding leaves the brushes. Brushes make contact with the next winding.

    For a brushless type to drive a load, your system needs to turn on a coil when it can 'do the most good', that is, when it will attract the coil to the next magnet.

    Then it must keep the coil energized for the amount of time that will do the most good, that is, while the coil approaches the magnet.

    Then it must turn off that coil at nearest approach to the magnet. These steps are similar to the brushed motor.



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  3. #3
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    Re: BLDC controller stuck at load condition

    Hi,

    Your attachments don't work. Most probably it took too much time from uploading the files to sending the post.

    * Give us the (link to the) full motor datasheet
    * show us your schematic and PCB layout
    * motor load in "kg" says nothing, give the load as torque in Nm
    * why is the "stall current" only 20A? Where and hiw did you measure it? Is there a current limiting scheme? How does it work? --> scope picture
    * Which Mosfet dies? Low side or high side?
    * do the Mosfets have proper heatsinks?
    * Is your bus voltage stable? Which value?

    Klaus
    Please don´t contact me via PM, because there is no time to respond to them. No friend requests. Thank you.



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    Re: BLDC controller stuck at load condition

    - Motor description

    Model: BM1418ZXF

    Rated Operating Voltage: 48V DC
    Rated Power: 500W
    Rated Speed: 2800 RPM
    No Load Speed: 3100 RPM
    Full Load Current: 13.4A
    No Load Current: 4.0A
    Efficiency: >75%
    Gear Speed: 400 RPM
    Gear Torque: 1.7N.m
    Gear Ratio: 6:1

    - Schematic

    Sry friend i can't show the full pcb or schematic design.
    Here is the single phase connection...
    Attachment 151718

    - Motor load
    1.34813276817e+19 torque newton meter

    - stall current
    Yes the maximum start current is above 20amp and i measure it with clamp meter. Even i starting at slow speed.
    I used 20 and 30 amp circuit breaker for safety. The circuit breaker (trip) get disconnected while applying.
    But when i compare that with Chinese controller, that controller works good. Chinese controller not even raising above 5amp at slow start (with load) .

    - Mosfet dies
    Only all the High side mosfets dies.

    - Heatsinks
    Yes i attached good heat sink

    - bus voltage stable
    sry i haven't checked it.

    - - - Updated - - -

    Quote Originally Posted by BradtheRad View Post
    Your switching system needs to do the same thing as the commutator in a brushed DC motor. The commutator does what it does automatically, because the forces of magnetic attraction pull the armature around to send juice through the next winding.

    Steps:
    1) A winding contacts the two brushes.
    2) Current flows in the winding.
    3) This creates magnetic force which pulls it toward a nearby opposite pole (magnet or energized coil).
    4) Armature turns a fraction of a turn.
    5) Winding leaves the brushes. Brushes make contact with the next winding.

    For a brushless type to drive a load, your system needs to turn on a coil when it can 'do the most good', that is, when it will attract the coil to the next magnet.

    Then it must keep the coil energized for the amount of time that will do the most good, that is, while the coil approaches the magnet.

    Then it must turn off that coil at nearest approach to the magnet. These steps are similar to the brushed motor.
    Yes friend i am energizing the two winding at a time. Trapizoidal controlling method with edge and conter aligned pwm.
    I am supplying ac current to the one pair of winding by keeping remaining one as free by this control method. Which works well at no load and amp rating was 1.9 at no load.
    I think i am able to product enough amount of starting torque?



  5. #5
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    Re: BLDC controller stuck at load condition

    Hi,

    - Schematic

    Sry friend i can't show the full pcb or schematic design.
    Here is the single phase connection...
    I assume this is not your actual schematic, it more looks like a simulation tool svhematic.
    If it is not your actual schematic, then it is simply useless.
    It's like: Your car does not work anymore and you give your neighbour's car to the garage...

    The PCB layout is critical. I'd say there is at least a 50% chance that the problem is caused by a bad PCB layout.
    --> It's your decision, whether we can help you or not.

    - Motor load
    1.34813276817e+19 torque newton meter
    Wow, 10 fractional digits. More precise than expected, but obviously wrong.
    With the given torque you may easily speed up the whole earth's RPM.

    Stall current: A lot of my questions are not answered.
    --> this makes it impossible to give good help.

    - bus voltage stable
    sry i haven't checked it.
    Your halfbridges need DC supply voltage.
    * What's voltage value?
    * It needs to be stable --> use a scope at one high_side_mosfet_drain during operation with load connected.

    Additionally you should give us a scope picture of the HIN and LIN signal of an active halfbridge...during operation with load connected.

    Klaus
    Please don´t contact me via PM, because there is no time to respond to them. No friend requests. Thank you.



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  6. #6
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    Re: BLDC controller stuck at load condition

    Quote Originally Posted by Nihaludeen View Post
    Here is the single phase connection...
    [ATTACH= CONFIG]151718[/ ATTACH]
    This attachment expired prematurely. Please post the diagram again, and submit your post quickly after uploading your image.

    - - - Updated - - -

    Note: It was by chance that I was able to convert images in post #1, because I still had them open in my browser tabs.



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