TITO system identification using relay with hysteresis

In this paper an on-line identification of two input two output (TITO) system using describing functions (DF) of relays with hysteresis is presented. In relay based system identification, describing function is widely adopted because of the ease of computation involved and general usefulness of the method. Measurement noise is an important issue in an identification problem. During the relay feedback experiments, amplitude of the limit cycle output is often corrupted with noises which may even fail the test. To overcome the possible failure, a relay with hysteresis is considered in the proposed identification method. The identification method developed for a second order plus time delay (SOPDT) system is extended for the TITO system. Simulation examples are included to illustrate usefulness of the proposed method for on-line identification of TITO systems.