By: Kevin Wang

A PID Controller is a device used in automation that adjusts a certain value to a desired target by comparing the current value with the desired target. For example, an air conditioner would need to sense the temperature of a room and adjust it to a desired temperature. The AC will sense the room’s temperature, compare it to a desired temperature, and then turn on the fans to reach that temperature accurately. According to Medium, “The difference between the Output value and the Setpoint value will give us the Error, and the goal of a PID Controller is to minimize the error by processing it.”

A PID controller works in a closed loop system, automatically working with zero human interaction. According to Geeksforgeeks, “PID controller” stands for “Proportional Integral Derivative Controller,” and this controller is “a combination of proportional, integral, and derivative action to regulate a process variable by adjusting a manipulated variable.” Proportional means that the further a value is from its target, the more the controller will push it to the target. Integral means that the longer the value isn’t where it should be, the more the controller will push the value to the target. Finally, derivative means that if the value changes too fast, put in power in the opposite direction of the change to slow down.

Here’s an analogy of an air conditioner utilizing a PID controller. A proportional controller can be made without using integral and derivative, but the value may stabilize below the target value. If this simple controller were in an AC, somebody’s room would be feeling chillier than it should be, so the AC programmer (let’s call him Bob) may increase the proportional gain. Unfortunately, the increased proportional gain would overshoot or oscillate a lot, so that person’s room will be too hot or keep going from cold to hot.

Instead of increasing the proportional gain, Bob might do some research and think of adding an integral control method. With this new Proportional Integral (PI) controller, the AC now boosts the fans’ power if the room is too cold for a certain amount of time. One day, somebody with the PI controller air conditioning opens a window while the air conditioner is running, so the room quickly gets very cold.

However, the PI controller can’t adjust to big changes quickly, so the person who opened the window has to suffer through a cold room.

Bob researches and discovers a derivative control method, which he adds to the AC controller, thus creating a PID controller. Now when somebody opens a window, the big dip in temperature will cause the AC to quickly adjust so the room heats up to a comfortable temperature.

PID controllers are used in real life to regulate flow, temperature, speed, pressure, and more. They can achieve great accuracy in a short amount of time and are relatively simple and efficient. However due to the 3 parts of the controller, the user would also have to tune 3 variables. The number of combinations the 3 variables have can lead to errors in creating an optimal set of variables for each use case. Despite this, PID controllers are used everywhere, from automotive and manufacturing to robotics and air conditioning.