am designing a BLDC hub motor (48V-500W-15A max)

I have designed a three phase inverter and the motor run normally with smooth rotation and as the motor start running and I apply the load the motor draw more current and every thing is normal.I am using PWM to control the speed

But the problem is that as I apply a load before the motor start to move even a very small load the motor do not start till we reach a high PWM value then the motor draw a very high current spike it reached a 26A then the motor start rotating at a fairly high speed. we run at 10KHz frequency.

So is there is an issue should I take care with at starting the motor on a load or this is a nature response and The only solution is to use very high rating components,,,

enter image description here

  • 1
    \$\begingroup\$ Aaaargh! Turn off the grid before taking a screenshot. It's unreadable. \$\endgroup\$
    – Transistor
    Commented Feb 12, 2018 at 20:20
  • \$\begingroup\$ Why do you have bootstrap components on your low side driver? \$\endgroup\$
    – user16324
    Commented Feb 12, 2018 at 20:31
  • \$\begingroup\$ What type of feedback? \$\endgroup\$ Commented Feb 12, 2018 at 20:43
  • \$\begingroup\$ @ John Birckhead,, the hub motor has a 3 hall sensors that sense the position \$\endgroup\$
    – Osama
    Commented Feb 12, 2018 at 20:44
  • \$\begingroup\$ @ Brian Drummond,, you are right this bootstrap is not important we worked just fine with or without it.. would this bootstrap make cause this starting problem? \$\endgroup\$
    – Osama
    Commented Feb 12, 2018 at 20:48

1 Answer 1


Actually the BLDC should deliver max torque at 0 rpm, also the max current. There must be a big flaw in your project, could be the synchronism, phase sequence, ....who knows? The information provided is just too little.


Looking at the schematics, there are a lot of wrong things. Like the diode on the gate signal is placed wrongly. The zener diode at the gate? Why do you need it, to add some extra capacitance, maybe?

  • \$\begingroup\$ ,, Thank you for our reply ,, the thing is the motor works fine as long as the motor start moving the only problem is when we put load before starting to move, \$\endgroup\$
    – Osama
    Commented Feb 12, 2018 at 20:46

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