Controllers & Feedback MCQ [Free PDF] – 5 Objective Questions with Answers

A PI controller adds an integrator pole at the origin and a finite zero, increasing system type and reducing/eliminating steady-state error for appropriate inputs. The assertion is therefore true. The reason is false because a PI controller's added pole is specifically at the origin; the finite negative-real-axis point is the controller zero, not an arbitrary added pole.

A PI controller introduces an integrator 1/s, so a first-order plant normally produces a second-order closed-loop characteristic equation: Statement 1 is true. For a standard plant K/(τs+1) with fixed K_p, ζ = (1 + KK_p)/(2√(τKK_i)); increasing K_i reduces ζ, so Statement 2 is false.

Statement 1 is false because negative feedback does not always guarantee stable closed-loop poles. Statement 2 is true because negative feedback can reduce parameter sensitivity; for a standard loop, S = 1/[1 + G(s)H(s)]. Therefore option C is correct.

Proportional action generally speeds response but leaves finite error; integral action raises low-frequency gain and can eliminate step steady-state error; derivative action adds predictive damping and can reduce overshoot. None of these by itself guarantees stability for every plant/tuning. Key relation: u(t)=K_p e + K_i∫e dt + K_d de/dt.

Exam focus: I fixes offset; D improves damping; P sets overall response strength. Common trap: PID is not an unconditional stability guarantee.

A controller processes the error/control information and modifies the control signal so the plant responds according to desired performance requirements. It may amplify, integrate, differentiate, shape or otherwise compensate the signal.