1. A method of automatically switching an adaptive PID controller comprising: defining a model set having a plurality of individual models representative of the controlled process, wherein each of the models includes a plurality of parameter values; defining a plurality of model subsets within the model set; wherein each of the model subsets includes a state parameter representative of a process variable input and a plurality of initial parameter values representative of the model subset; determining the state parameter and updating the PID controller with the plurality of initial parameter values associated with the state parameter; evaluating each of the models in the model subset corresponding to the state parameter and calculating a model squared error for each model; determining an adaptive parameter value as a function of the model squared error; and updating the PID controller in response to the adaptive parameter value.