Performance improvement of unsymmetrical processes using sliding mode control approach

An unsymmetrical process is one that consists of two operating modes with different dynamics in each mode. The most common approach to control unsymmetrical processes is the use of gain scheduling where two sets of controller parameters are used for the two different modes. In this paper, the sliding mode control (SMC) approach is adopted for control of unsymmetrical processes. It is shown by examples that using the dynamics of one of the modes to obtain the control law based on the SMC approach gives satisfactory closed loop performance for the other mode as well. This provides several advantages. First, the need for identification and controller design of the two different modes has been eliminated. Second, a robust closed loop control system to modeling errors or parameter changes has been achieved. Finally, a closed loop system with better set point tracking and disturbance rejection has been obtained.