Linear approach to performance assessment of a 4-tank system

Monitoring performance of nonlinear system is an important task for many real world applications especially for industrial environments; however its realization is usually difficult. Many monitoring performance methods have been introduced but they all rely on loops with accurate linear models of the system. The methods that are capable to identify MIMO nonlinear systems are scarce and linear models are not so accurate in modeling nonlinear systems. In this paper, a combined series of two capable algorithms is used for identifying the system. The method also identifies the existence of any possible disturbance simultaneously in order to reduce the complexity of the model. The logic behind the proposed methods is to utilize and approximate the interaction between the loops in the system. Moreover, the model explicitly defines the relationship between the outputs and the inputs of the system such that the performance indexes can be easily calculated. A well designed control strategy is introduced to determine the optimal values that are required to calculate the performance index. A reasonable decision on optimal situation is necessary to evaluate the performance index of a system. A minimum variances control strategy (MVC) is considered here as the most suitable feedback controller because it achieves the smallest possible closed-loop output variance. The above method has been utilized for a 4-tank system and then a minimum variance controller is designed for determining the optimal output such that the minimum possible variance, and consequently the performance index have been calculated. The achieved Index can be then used for monitor performance of systems in online and offline applications.