In my current implementation of sensorless foc startup I run the motor open loop using a constant current for a preset time and then try to close the loop. Currently I'm able to do this within 400ms but I'd like to shorten this time further and preferably have a routine that can start the motor with maximum torque right away most of the time.
My implementation is very similar to the one described in this app note: http://ww1.microchip.com/downloads/en/AppNotes/01078B.pdf
The rotor position is estimated using sliding mode observer and stabilizes after a while of running the motor open loop.
I'm a bit concerned though about the reliability of such startup and the fact that it takes 400ms and does not deliver maximum torque when the rotor is not aligned. What other ways can I use to achive quickest startup with maximum initial torque on this type of setup that does not use any kind of position sensor?