What Is a PID Controller?
A PID controller is a popular feedback control system that continuously calculates an error value between a desired setpoint and a measured process variable, and applies a correction based on proportional, integral, and derivative terms. This control method is widely used in industrial automation, robotics, HVAC, motor drives, and any application requiring stable closed-loop control.
Understanding the Three Components: P, I, and D
Proportional (P):
Reacts instantly to the current error. The larger the error, the stronger the correction. This term provides immediate response but may leave steady-state error.Integral (I):
Sums past errors over time. It works to eliminate residual offset that P alone can’t correct. However, excessive integral action can cause instability.Derivative (D):
Predicts future error trends by evaluating the rate of change. This anticipatory action helps dampen oscillations and improve settling time.
Combined, these three terms form the core of a PID control algorithm, tuned with gain constants: Kp, Ki, and Kd.
PI vs PID: Which Is Better?
| Feature | PI Controller | PID Controller |
|---|---|---|
| Components | Proportional + Integral | Proportional + Integral + Derivative |
| Use Case | Slower, stable systems (e.g. temperature) | Fast-changing systems (e.g. motor control) |
| Tuning Difficulty | Easier | More complex |
| Overshoot Control | Moderate | Better with D term |
In many embedded systems, PI controllers are sufficient. But when precision and fast response are critical, the PID controller provides superior dynamic performance.
How Does a PID Controller Work?
A PID controller works by continuously monitoring the difference between the setpoint and the measured process variable, then adjusting the actuator output through a feedback loop to minimize the error. This process is known as a PID loop.
Time Delay & Overshoot Adjustmen
PID controllers can suffer from time delay and overshoot if poorly tuned. Here’s how each term addresses those:
Proportional (P): Reduces present error, but may cause overshoot.
Integral (I): Eliminates steady-state error, but adds lag.
Derivative (D): Dampens response, reducing overshoot and improving stability.
Below is a typical PID step response graph:
| Type | Overshoot | Stability | Reaction Time |
|---|---|---|---|
| P Only | High | Poor | Fast |
| PI | Medium | Good | Moderate |
| PID | Low | Best | Fastest |
