In a unity feedback system, which term primarily eliminates steady-state error?

• A. Integral term
• B. Proportional term
• C. Derivative term
• D. Feedforward term

Answer: (A)

In a unity feedback loop, steady-state error is the persistent difference between the reference input and the output as time goes on. The integral action adds a term that accumulates the error over time, so even a small, constant offset keeps growing the controller’s corrective signal. This continuous accumulation pushes the output to match the reference, driving the steady-state error toward zero. The derivative term reacts to how quickly the error is changing, not to a constant offset, so it doesn’t eliminate steady-state error. The proportional term reduces error in the moment but leaves a constant offset when the input is steady. Feedforward can help tracking, but it doesn’t inherently cancel the persistent offset in a feedback loop. So the integral action is the mechanism that primarily eliminates steady-state error.