Sliding mode control of coupled tank systems using conditional integrators

Abstract

For the problem of set point regulation of the liquid level in coupled tank systems, we present a continuous sliding mode control ( SMC ) with a “ conditional integrator ” , which only provides integral action inside the boundary layer. For a special choice of the controller parameters, our design can be viewed as a PID controller with anti-windup and achieves robust regulation. The proposed controller recovers the transient response performance without control chattering. Both full-state feedback as well as output-feedback designs are presented in this work. Our output-feedback design uses a high-gain observer ( HGO ) which recovers the performance of a state-feedback design where plant parameters are assumed to be known. We consider both interacting as well as non-interacting tanks and analytical results for stability and transient performance are presented in both the cases. The proposed controller continuous SMC with conditional integrators ( CSMCCI ) provides superior results in terms of the performance measures as well as performance indices than ideal SMC, continuous SMC ( CSMC ) and continuous SMC with conventional integrator ( CSMCI ) . Experimental results demonstrate good tracking performance in spite of unmodeled dynamics and disturbances.