Control Systems (Electrical)

Control System Basics:

• Open loop: no feedback. Inputs determine output. E.g., washing machine timer.
• Closed loop: feedback. Output measured, compared to setpoint. E.g., thermostat.

Components:

• Plant / Process: what you control.
• Controller: decides what action to take.
• Sensor: measures output.
• Actuator: acts on plant.

Transfer function: G(s) = Y(s)/X(s) = output/input in Laplace domain.

Stability:

• Stable: bounded input → bounded output.
• Routh-Hurwitz criterion: check if all roots have negative real parts.

Standard test signals:

• Step: sudden change.
• Ramp: linear increase.
• Impulse: instantaneous spike.
• Sinusoidal: for frequency response.

Time domain specs:

• Rise time, peak time.
• Settling time.
• Overshoot.

Frequency response:

• Bode plot: gain & phase vs frequency.
• Gain margin, phase margin (stability).

Controllers:

• P (Proportional): output ∝ error.
• I (Integral): removes steady-state error.
• D (Derivative): dampens oscillations.
• PID: combination, most common in industry.

PLC (Programmable Logic Controller):

• Industrial automation.
• Ladder logic programming.

Modern control:

• State-space.
• Adaptive control.
• Robust control.

Applications:

• Robotics.
• Aerospace (autopilots).
• Industry (manufacturing).
• Railways (KAVACH train protection).

RRB JE focus: open vs closed loop, PID basics, simple stability concepts.