Nonlinear observer design for a solar thermal water heater system

A nonlinear observer is constructed to observe the two unobservable states of the solar thermal system from the heat exchanger. At first, we discuss the observability of the model and four cases are discussed based on the variation of the model parameters. Then, we design full-order observer when the system is observable. Especially, we design a finite-time observer for one case. At last, a simulation is created for the solar thermal system model. The result is that the unobservable states of the solar thermal system can be estimated fairly closely to the model data by using the nonlinear observer.