Double feedforward compensation for cascade control schemes

This paper addresses the problem of dealing with measurable disturbances in cascade control schemes. The combination of cascade and feedforward control algorithms is analyzed. The design of a static feedforward compensators control scheme to assist the controller in the rejection of measurable disturbances is a widely accepted solution in the literature. This article proposes a new solution by implementing two static feedforward controllers, one in the outer and other in the inner loop, as part of the cascade control scheme. The tuning rules for the feedforward compensators are proposed to enhance the process performance for the load disturbances rejection problem. Simulation examples demonstrate the advantages of the proposed solution by improving the process output performance while reducing the control effort. Moreover, the new solution is evaluated in simulation on two non-linear typical processes in chemical industry, a tank level control and concentration control in a Continuous Stirred Tank Reactor (CSTR).