Performance Assessment for Completely Unknown SISO and MIMO Systems Based on Gain and Phase Margins Using Modified Relay Feedback

A performance assessment procedure for single-input-single-output (SISO) and multi-input-multi-output (MIMO) systems based on modified relay feedback test is proposed in this paper. The well-known robustness measurements, gain and phase margins, are used to assess the performance of the control systems. The proposed method can on-line estimate the gain and phase margins for systems with both unknown controller parameters and process dynamics by a modified relay feedback scheme where a delay element is embedded between the relay and controller. The estimated results can be used to indicate the appropriateness of the controller parameters. When the retuning of controller is found necessary, a similar procedure can be applied to tune the PI/PID controller based on specifications of gain and phase margins. Performance assessment and controller design can be done simultaneously, which ensures a good performance of the control system.