Performance and robustness of lowpass filter feedback for already-established control system

When a closed-loop control system is already established but its control performance is not satisfactory, there is a need either to change a closed-loop controller itself or to insert an additional compensator into an already-established control system in order to satisfy a desired control specification. A simple control performance improvement method is proposed by attaching only a lowpass filter feedback to the already-established closed-loop control system. The lowpass filter feedback is interpreted as an integral controller and a lead compensator. Its performance and robustness properties are discussed.