Glossary · Control theory and process control
PD controller
Also known as: Proportional-derivative controller
German: PD-Regler
In control engineering, a PD controller combines proportional and derivative action: its output depends on the current control error and on its rate of change, which adds damping but leaves a steady-state error when a constant load acts on the process.
- Control theory
In one sentence
A PD controller combines proportional and derivative action for fast, damped response, but without integral action it can leave a steady-state error.
Example
A position loop on a servo axis uses PD control because the integrating behavior of the axis already removes steady-state position error for constant setpoints.
How it applies
- Engineering: PD control suits processes that already integrate, such as position from velocity, where integral action would add phase lag without much benefit. Derivative action needs filtering because it amplifies noise.
- Commissioning: Check for steady-state offset under load; if it is too large, integral action or feedforward is needed.
- Documentation: Where a PID block is used with integral action disabled, say so explicitly in the control description, because readers assume PI or PID by default.
- Maintenance: When a mechanical change alters the load or friction, recheck the steady-state error and the damping, since both depend on the proportional and derivative settings.
PD controller vs. PI controller
The PD controller adds damping and speed; the PI controller removes steady-state error. Most process loops use PI, most motion position loops use P or PD with a subordinate speed loop.