Motor start is different on each cycle using STEVAL-PTOOL4A

[AnthonyK]

Hello,

I am using the STEAVL-PTOOL4A to drive a BLDC motor using the FOC with hall sensors. The motor is running ok but I noticed that during the start of the motor, the speed does not reach its final value at the same time. I mean there is a noticed difference. Sometimes it is slow, sometimes it is fast. I increase the bootstrap Capacitor time from 10ms to 1000ms I still have some differences but lower when I had 10ms. 

Here are some plots when the speed reaches its target fast

And here when it is slow:

I took the Valfa and Vbeta since it could be related to the Capacitor voltage. So I noticed as if the startup of the capacitor does not have the same duration.

Could someone explain why I have this behavior?

Thank you

[GMA]

Hello @AnthonyK,

Running STEAVL-PTOOL4A to drive a BLDC motor using the FOC with hall sensors on MC MCSDK6.3.2 version with a motor with no load, I did not notice such behavior.

Do you have a load on your motor or a limiter on your DC supply?