


Proportional Control 



Let’s adjust our car control environment a little more to examine a limitation in proportional control. We are driving along a flat road with our proportional control of the pedal responding to changes in the speedometer reading when suddenly we start to climb a steep hill. The speed drops very quickly and we match the drop by a carefully proportioned depression of the accelerator. The net result is that eventually we get back up to 30mph but only after we have dropped right down to about 10. We could see the speed dropping quickly but we constrained ourselves to only apply a fixed proportion of accelerator based on the difference between actual speed and target speed. What we feel we needed to do is produce a lot more accelerator power than we actually needed for a short duration to counteract the sudden decrease in speed followed by a more proportioned response. How do we relate this “gut” feeling to control theory? The answer is derivative control. 

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