The objective of this study is to design robust direct model reference adaptive controller (DMRAC) for a non-linear cardiovascular model over a range of plant parameters representing a variety of physical conditions. The direct adaptive controllers used here require the plant to be almost strictly positive real (ASPR), that is, for a plant to be controlled there must exist a feedback gain such that the resulting closed-loop system is strictly positive real. We designed new compensator so that the system composed of the cardiovascular plant and the compensator satisfies the ASPR condition.
Numerous technical papers have considered a small range of gain variations of the cardiovascular system. In most of these works, the controller was designed based on the variations in either time delay or plant gains. Many of the papers have treated the cardiovascular system as a single-input single-output (SISO) plant in which the control output was mean arterial pressure (MAP). We treated the cardiovascular system as a multi-input multi-output (MIMO) plant in which both the MAP and cardiac output (CO) are controlled.
We presented a new linear model that provides better approximation than the original linear model. By doing so and utilizing the DMRAC algorithm, we could satisfy the stability conditions for the model, and obtained satisfactory responses in every possible condition for the cardiovascular nonlinear model.