P only controller/PID - overshoot

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The discussion centers on understanding how a proportional controller functions in cruise control systems, particularly regarding overshoot. When the error becomes negative, indicating the vehicle is exceeding the desired speed, the output of the controller also turns negative, suggesting a reduction in thrust. However, since thrust cannot go below zero, the car instead engages braking. This process allows the motor to act as a generator, recharging the battery and promoting energy efficiency. Overall, the conversation highlights the balance between maintaining speed and managing overshoot in vehicle control systems.
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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.

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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?
 
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Herman Oen said:
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 ).
 
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