Robust Digital LQ Control of Time-delay Systems

Time-delays are mainly caused by the time required to transport mass, energy or information, but they can also be caused by processing time or accumulation. Typical examples of such processes are e.g. pumps, liquid storing tanks, distillation columns or some types of chemical reactors. This paper deals with a design of universal and robust digital control algorithms for control of great deal of processes with time-delay. These algorithms are realized using the digital Smith Predictor (SP) based on polynomial approach – by minimization of the Linear Quadratic (LQ) criterion. For minimization of the LQ criterion is used spectral factorization principle with application of the MATLAB Polynomial Toolbox. The designed polynomial digital SPs were verified in simulation conditions (and also using an experimental model of a laboratory heat exchanger). The main contribution of this paper is an experimental simulation examination of the robustness of the designed control algorithms. The program system MATLAB/SIMULINK was used for this purpose. Key-Words: Digital control, LQ control, Polynomial approach, Simulation of control loops, Smith Predictor, Time-delay, Robustness.