BOOSTXL-DRV8323RS: Open loop acceleration equations and parameters

Mohamed Saeed

Part Number: BOOSTXL-DRV8323RS
Other Parts Discussed in Thread: MSP430F5529, DRV832X

Hello,

I am trying to understand the open loop acceleration reference code in the project DRV832X_MSP430F5529_Trapezoidal_Sensorless_BLDC.

At MOTOR_START state when open loop acceleration is applied, a startup duty cycle is applied (25%) and the distance traveled is estimated using 2 parameters.

AccelRate which is 40 Hz/s in the reference code.

ACCEL_60_DEGREES which is 20834 in the reference code.

Every 1 ms this happens:

-Velocity is increased by the AccelRate.

-Distance is increased by (Velocity + AccelRate/2 )/8.

My question is why is this equation used to calculate the distance and how the ACCEL_60_DEGREES parameter is calculated?

Also is there any technical reference explaining the theory behind this method?

over 5 years ago

0 Adam Sidelsky over 5 years ago

TI__Guru 65220 points

Mohamed,

Thanks for posting on the MD forum!

Could you show a screenshot of the code you're mentioning?

Regards,

-Adam

0 Mohamed Saeed over 5 years ago in reply to Adam Sidelsky

Intellectual 310 points

Thanks Adam for your reply,

Here is a screenshot.

0 Adam Sidelsky over 5 years ago in reply to Mohamed Saeed

TI__Guru 65220 points

Mohamed,

I'm checking into this with the team.

Regards,

-Adam

0 Adam Sidelsky over 5 years ago in reply to Adam Sidelsky

TI__Guru 65220 points

Mohamed,

The MOTOR_START code is attempting to blindly accelerate the motor in open-loop mode.

AccelVelocityInit is the current velocity.

Assuming a constant acceleration and changing velocity, to find the velocity average at the time of integration, we take (Velocity1 + Velocity2) / 2, this is given by the AccelRate and the logical shift of ">> 1" gives us the divide by 2.

The code needs a count per revolution so that it can then calculate ACCEL_60_DEGREES

Assuming 1Hz/S rotation and Integrating 1000mHz for 1000mS we get ~1M counts for one motor revolution.

360/60 = 6 so our ACCEL_60_DEGREES should be ~1M divided by 6 or ~166,667 counts.

The variables selected for this are 16 bit so ~166k is too large. We therefore divide everything by 8 to make it fit and arrive at ~166k / 8 or 20834.

Regards,

-Adam

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BOOSTXL-DRV8323RS: Open loop acceleration equations and parameters