No abstract

The coupled tanks process is a two input-two output system. It presents a nonlinear behavior and interactions characteristic. After the nonlinear model is obtained, it is linearized around an operating point. A fractional-order proportional–integral–derivative based on the internal model control paradigm (1DOF-IMC-PID-FO) multi-loop controller is determined without considering the interactions, and a fractional-order proportional–integral–derivative based on the 2-degree-of-freedom internal model control structure (2DOF-IMC-PID-FO) multi-loop controller is determined by considering the interactions. Thus, an interactions reduction effect controller is calculated. Both controllers are implemented on a real-time process using the Real Time Windows Target of MATLAB. The objective of the control is to maintain the water level in the lower tanks at desired values. In the experiment, setpoint tracking and disturbance rejection tests are carried out to assess the performance of both 1DOF and 2DOF-IMC-PID-FO multi-loop controllers.

This paper is aimed to propose a multiloop control scheme for fractional order multi-input multi-output (FO-MIMO) systems. It is an extension of the FO-multiloop controller design method developed for integer order multivariable systems to FO-MIMO ones. The interactions among the control loops are considered as disturbances and a two degrees-of-freedom (2DOF) paradigm is used to deal with the process outputs performance and the interactions reduction effect, separately. The proposed controller design method is simple, in relation with the desired closed-loop specifications and a tuning parameter. It presents an interest in controlling complex MIMO systems since fractional order models (FO-models) represent some real processes better than integer order ones and high order systems can be approximated by FO-models. Two examples are considered and compared with other existing methods to evaluate the proposed controller.