Identifying an Unstructured Flexible Nonlinear Model for the Cascaded Water-tanks Benchmark: Capabilities and Short-comings

In this case study, we will illustrate the capabilities, flexibility and short-comings of an unstructured nonlinear modelling approach applied to the cascased tanks system benchmark problem. This benchmark combines soft and hard nonlinearities to be identified based on relatively short data records. The major identification challenges associated with this benchmark problem are: 1. the hard saturation nonlinearity combined with the weakly nonlinear behavior of the system in normal operation, 2. the overflow from the upper to the lower tank, this effect also introduces input dependent process noise, 3. the relatively short estimation data record. 4. the unknown initial values of the states.