Take your star /jerry case.
It would start in star , the condition you need for low winds. At a certain speed it will change to jerry, the connection you need for high winds. Ideally you change at the point where star is becoming inefficient and you would do better with Jerry. Probably at this point your prop will be on the slow side as you are getting bogged down in star. When you change to jerry the prop will get away so it is a stable change and the increased speed will hold it.
When the wind drops you need to change back when you are just above cut in speed for jerry and when it changes to star you will see a speed drop and again it will be stable. There is no need for any hysteresis to prevent it constantly changing mode..
The thing that will most likely determine the switching speed is the change back to star. You don't want it too late or you will spend time idling in Jerry when it ought to have been in star.
On low wind days it will probably stay in star. On high wind days it will most likely spend the majority of the time in jerry but I have never seen wind conditions where it doesn't change back occasionally. Perhaps there sites where this is true.
On many days it will be doing a lot of changing. This will be true however you do the change over. If you try to devise some clever way to get it truly at the optimum point it will spend its life changing most of the time and unless you can devise an electronic switching scheme it will hammer a relay to bits in very short time.
It is crude but does significantly improve things over direct connection. There are infinitely better ways to do the job so I didn't use it except for one machine and that was a little 5ft thing and also a 3ft machine that I did for a boat that needed simplicity for the owner, he could wreck most things and an electronic solution would have been difficult as it got disconnected and all manner of things.
Give it a try, try speed and try your idea and come back and tell us how you got on. you will never sort it pondering theory here, there is always a hidden snag in practice with anything associated with wind power.
Flux