A new framework for two loop disturbance rejection control

In this paper, a new framework of a two loop disturbance rejection control and its design methodology are proposed. The framework consists of a robust internal-loop compensator (RIC) to eliminate disturbances and an external-loop controller to achieve nominal control performance. As the main contribution of this paper, we define the design problem of the RIC as a regulation control problem, then show that this new definition with the RIC structure provides more design flexibility and less implementation constraints, which allows us to design the RIC aggressively against a specific disturbance. This is verified through a comparative structural analysis with a disturbance observer (DOB) and an adaptive robust control (ARC). Two design examples of the RIC are given, along with practical issues that should be considered in the design procedure. The proposed framework is demonstrated by simulations and experiments.