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Longer deadtime or blanking time between two mosfets of one leg phase U or v or w

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vishjay

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Hi,
Can the longer dead time cause distortion in output waveforms? And as a result torque ripple??
And can we perform the operation also without giving deadtime in bldc motor control?
 

Speaking with class-D/inverter experience but not motors: yes dead time creates distortion. When neither fet is on the result may be high, low or somewhere in between. The uncertainty creates distortion (specifically around the zero current crossing).

You can't decrease dead time without creating risk of 'shoot through' which can increase losses at best and blow up your fets at worst.

In real life a constraint on dead time is driver propagation delay uncertainty. If there is 10ns of uncertainty then you can't set dead time less than 10ns without risking shoot-through.

If you really need to minimize deadtime then look for modern half bride drivers with optimized dead time setting:
https://www.silabs.com/documents/public/data-sheets/Si824x.pdf
 

Deadtimes create a current sign dependent error in average output voltage, due to shift of actual commutation time. It's often compensated by "intelligent" pwm controllers.
 

Can the longer dead time cause distortion in output waveforms? YES

And as a result torque ripple?? YES - but usually quite small

And can we perform the operation also without giving deadtime in bldc motor control? NOT really NO
 

Thank you all for the answer.
On full duty cycle, i can’t see deadtime on scope perfectly. I increased to the max voltage and then i can see deadtime in scope. But on both pulses there is no clear pulse instead there is little under and over compensated pulse. How to see clear pulse without compensations?
 

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