P only controller/PID - overshoot

[Herman Oen]

Homework Statement

I am trying to understand the Proportinal controller, used as a cruise controll for a car. I do understand how it works as long as there are no overshoot.

Homework Equations

The Attempt at a Solution

The reason why I do not understand overshoot is because the error then gets negative and then the output also gets negative (out=Kp*error). This means negative thrust? You can never give less thrust than 0, so what is actually happening when the error gets negative?

 

[Hesch]

You can never give less thrust than 0, so what is actually happening when the error gets negative?

The car will brake.

The motor will act as a generator, and will charge the battery ( having a "green energy drive" and an electric motor ).