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high speed mode -- 100% PWM duty cycle and over-modulation

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Joined: 2017-05-24 12:46
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high speed mode -- 100% PWM duty cycle and over-modulation

The duty cycle limit (95%)  is present to:

  1. ensure charging of the high side gate driver power supply capacitor,
  2. allow phase current measurement during null vectors, a certain duration is needed to avoid switching noise in the measured current 

The capacitor anyway get charged at least once for each electric revolution even at 100% duty cycle and max over-modulation.  So the duty cycle limit should only be needed at low RPM. This raises the question: How often does the high side capacitor need to be charged?  (What i "low" RPM?) 

The current measurement can be moved to other vectors than the null vectors -- VESC-6 has inline phase shunts, so it can be done in any vector -- in particular it can be moved dynamically to the vectors with longer duration.

If I understand the duty cycle limit correctly; it comes into action twice per PWM cycle --  5% during V0 and 5% during V7 -- so removing this limit would give 11% higher voltage to the motor = 11% higher RPM,  .  Adding over-modulation (removing the circle limit) can add another 11% or so. 

Who wants 22% more power? 

flyingbrike's picture
Last seen: 7 months 4 weeks ago
Joined: 2020-05-14 15:39
Posts: 10

Hello. I wonder if you can help me. I AM A NEWBEE IN vesc.

I have converted car alternator running  both in FOC and BLDC fine. But there is a rpm limit at about 37000erpm. Battery is 16s 67v.

As i calculated , the motor can handle 10000rpm.  So i want to run 80000erpm ,as i have 8 polepairs.

What  settings should i tweak to achieve this?

Silent Revolution is NOW !

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Joined: 2016-12-27 20:19
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If the KV value of the motor is too low, you will have a hard time to drive it faster. Field weakening will make it spin faster, but it has the downside that you inject additional currents and generate additional losses and heat.