Constraint Handling in ESC Control Strategies with Application to HVAC Systems

When applying ESC to a complex system, internal variables within the system may be subject to constraints that cannot be handled explicitly by limiting the range of the variable(s) manipulated by ESC. This is particularly evident in HVAC systems where ESC is often used to minimize energy use but where internal variables need to be constrained to satisfy comfort requirements. To address this problem, the paper proposes the use of penalty functions that are incorporated in the objective function. This approach is generally applicable because mathematical information about the relationship between the constrained variables and the ESC manipulated variables is not required. The paper describes the application of penalty functions to two types of HVAC systems: variable refrigerant flow (VRF) systems; and roof-top air-conditioners. Different penalty function formulations are described and results are shown from tests on detailed simulation models.