The Effect of the Approximation Method for Large Time Delay Process on the Performance of IMC-PID Controller

For complex systems with time-varying, nonlinearity, and large time delay, the IMC-PID controller designed using the internal mode control strategy can be used to improve the control performance. Different setting formulas for IMC-PID controller parameters can be obtained by using different approximation methods for processing the time-delay process. These methods have a great influence on the control effect. The first-order Taylor, the first-order Pade, the second-order symmetric Pade and the second-order asymmetric Pade and all-pole approximation are used to obtain the parameter setting formulas, respectively. Their adaptabilities to large time-delay, large-inertia process and to large time-delay, small-inertia process are studied. The simulation results show that the all-pole approximation is more adaptive to the application of large time delay. The second-order symmetric Pade approximation is more effective in the large time-delay, small-inertia process, whereas the second-order asymmetric Pade approximation is more adaptive to large time-delay, large-inertia process.