Time delay is one of the common cases in industrial processes such as chemical and metallurgical industries. The controlled value cannot reflect the dynamic change of systems under disturbances because of the existence of time delay. It also results in significant overshoot, longer settling time and even instability of the system. Therefore, the time-delay system (TDS) is more difficult to control.
A lot of control methods have been proposed to overcome the impact of time delay. The complexity of time-delay systems such as long time delay, nonlinearity, stochastic uncertainty and multivariable coupling characteristics limit the application of the existing control theories and methods to actual systems.
ADRC (active disturbance rejection control) is an effective method to solve the control problem of complex structure (nonlinearity, uncertainty, coupling, etc.) systems. The core idea of ADRC regards the integral form as a standard form of feedback system. System dynamics different from the standard form are treated as total disturbance including internal disturbance and external disturbance. A complex system with full disturbance, uncertainty and nonlinearity can be reduced to a linear, canonical form.
Several control strategies based on ADRC have been proposed to handle time delay. According to those strategies, it can be concluded that time delay parameter τ is of vital importance. However,τ may be a time-varying parameter changing with working conditions in real industrial processes.
Kim Ha Su, a researcher at the Faculty of Metal Engineering, has proposed a predictive active disturbance rejection control with adaptability (AD-PADRC) to solve the control problem of a time-varying delay system.
The proposed method is based on the integration of a PADRC and an estimation module for adaptive delay. First, a time-delay system is controlled by PADRC. Then, the time-varying delay is estimated via correlation technique. The minimum variance principle is used as a benchmark to monitor the control performance of a time-varying delay system under AD-PADRC.
The simulation results have proved the efficiency of AD-PADRC when the time delay changes on a large scale.
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