Multivariable control of the bifurcation and harmonic perturbations to improve the performance of air-handling units

In this research, nonlinear dynamics of an air-ehandling unit (AHU) is studied for tracking objectives, in the presence of harmonic perturbations. Three arbitrary realistic set-paths are considered for the indoor temperature and relative humidity. Two controllers based on feedback linearization (FBL) and pole placement approaches are designed to preserve the dynamic system around the desired tracking paths. It is shown that FBL controller works efficiently in bifurcation control and transforms the quasi-periodic limit cycles into the periodic ones (and consequently comfortable indoor conditions). In addition, FBL controller guarantees suppression of larger periodic limit cycles into the smaller ones, while it requires the lower air and cold water flow rates with less oscillatory behavior (in comparison with the pole-placement controller). However, it is observed that FBL controller fails in bifurcation control when the disturbance frequency increases. Re-tuning the dynamic gains of FBL controller is essential under such conditions.