Other Parts Discussed in Thread: DRV8301
Hello -
This post is in reference to a post from Dave Wilson made some time ago:
Hi Ben,
By using Hall sensors at zero speed, you should be able to get performance that is at least as good as commutated trapezoidal control. Have you tested your application with trap control yet to see if that is good enough to meet your requirements? The problem is that unless you have uniform flux density in the airgap of your machine, you will experience varying levels of torque depending on what angle you are at within the commutation interval.
I think mode switching could be accomplished on the fly rather seamlessly. The FAST angle estimator can be enabled, even if its output is not being used by the FOC control loop. So you could use commutated control at low speeds. Whenever a hall sensor causes a commutation event, at that moment you should know what the motor angle is with reasonable accuracy. Immediately compare the FAST angle estimate to this value, and if you are spinning fast enough to get good angle correlation, then switch over to the FAST observer.
-Dave
(source: e2e.ti.com/.../1042520)
I want to implement exactly what Dave has suggested. I currently have lab 11e (MW 17) ported to work on my custom hardware (DRV8301/F28027F) and it works fine. I would like to modify this so that FAST/FOC takes over as soon as possible (as opposed to at a set transition speed). I need to understand how to go about tracking angle correlation, and therefore triggering when to switch to FAST/FOC.
Can I simply take the electrical angle which corresponds to the current hall sensor state (one of six possible angles) and compare this to the current FAST estimate? If they match within a tolerance can I assume it is safe to switch over to FAST? Or is there some other consideration I need to take into account?
Also, assuming with this approach that I should never use ForceAngle, correct?
Any help is appreciated.
Best,
-asifjahmed
