Control of Vapor Compression Cycles under Transient Thermal Loads

Evaporator Disturbance Rejection in Vapor Compression Cycles with a Linear Quadratic Regulator

“…From these case studies, we've seen that the advantages of using LQR over PI are not so clear cut, as was suggested in previous work [9]. The LQR controller manages to respect all of the constraints set by the controller specifications, whereas the PI controller fails to maintain the minimum level of superheat.…”

“…This paper aims to further that research effort by designing an linear quadratic regulator (LQR) controller, augmented with integral control, to investigate the potential for rejecting large heat pulses in the evaporator. In our previous work, we developed an LQR integral controller for a simple vapor cycle with only a single evaporator [9]. This paper extends those results by studying a dual-evaporator system, with an added liquid injection valve, based on a previous system studied by AFRL [2].…”

“…Unfortunately, this source of error is difficult to mitigate in the framework of linear control theory. However, our analysis suggests that a significant amount of the steady state error is caused by the feed-forward term introduced in the residualization step of model reduction [9]. When introducing integral control to the regulator, there is a feed-forward term that is ignored, because these feed-forward terms are known to cause instabilities whenever any modeling errors are present.…”

“…This paper presented simulation results comparing the performance of LQR and PI control in a dual-evaporator vapor cycle, in extension of the results presented in [9]. LQR outperformed PI in superheat regulation by a wide margin, but PI outperformed LQR in all of the other categories by a small margin.…”

“…The new controller differs from the PI architecture, in that it is based on a linear model, and it is multiinput multi-output (MIMO), so as to account for cross-couplings between the different actuators and sensors. The design process for creating this new controller was covered in depth in [9], with Fig. 2 providing an overview of the techniques used.…”