A cascade iterative learning control scheme for a class of repetitive cascaded processes

In many industries, the cascaded manufacturing process usually consists of a fast response sub-process with disturbance and a slow response sub-process with large time delay. For a repetitive cascaded process with such characteristics, a new cascade iterative learning control (ILC) scheme is proposed in this paper. For the slow response sub-process with good repetitive dynamics, an ILC is firstly designed as the outer loop control under the framework of the two-dimensional generalized predictive control to guarantee the stability and convergence of the control performance from cycle to cycle, and then a real-time model predictive control, the inner loop control, is designed with the optimal control sequence ordered by the ILC law as the control reference at every control instant to ensure a good disturbance rejection for the non-repeatable disturbances. As the different control schemes are applied to the sub-processes with different natures, the control performances of the system is superior to the traditional ILC scheme, which is demonstrated by the numerical illustrations.