On-line monitoring for multiloop control systems under load disturbance

Abstract

Recently, relay based on-line monitoring procedures were proposed to identify the maximum closed-loop log modulus, L(c,max), for both SISO and multiloop control systems. However, the frequent load disturbances in the processes can usually distort the oscillations generated in the relay experiments. Consequently the identified L(c,max), which is calculated from the system stationary oscillations, will be less accurate. In this paper, an efficient procedure for tuning the relay bias is proposed to counteract the effect of load disturbances. Simulation results including a nonlinear stirred mixing tank example are used to illustrate the effectiveness of the proposed monitoring procedure.