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BLDC controller stuck at load condition

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Nihaludeen

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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

back emf.png

View attachment 151650

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

phase to phase voltage with pwm.jpg

**broken link removed**

phase to phase voltage without applying pwm....

phase to phase without applying pwm.jpg

**broken link removed**

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
Block Diagram for a Brushless DC Motor.png

commutation sequence
clockwise...
CommutationTable_CW.png
 
Last edited by a moderator:

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.
 

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
 

- 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...
**broken link removed**

- 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 - - -

BradtheRad said:
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.
Click to expand...

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?
 

Hi,

- Schematic

Sry friend i can't show the full pcb or schematic design.
Here is the single phase connection...
Click to expand...
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
Click to expand...
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.
Click to expand...
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
 

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