Passive Control: Control introduced in system due to design. Does not need additional energy to function. e.g. Truck shape introducing drag to keep it from lifting
Active Control: Control introduced in system by use of external energy. Types:
Open Loop: No feedback in system which results in continuous inputs.
Closed Loop: Introduces feedback system using sensors which can be used for minute control which varies based on output of the system.
Why Feedback is needed?
Uncertainity: System often has uncertainity which renders preplanned input useless.
Instability: System might be unstable due to external noise. Feedback can result in better control.
Disturbance tends to pass through system dynamics and can be measured to improve control over it.
Efficient: Introducing feedback results in overall lower energy consumption due to applied force being proportional to present error, thus reduces overall lower energy.