Control structure design and dynamics modelling of the organic Rankine cycle system

In this paper, the control structure for the organic Rankine cycle (ORC) system is proposed. This control structure is derived by using the state space model of the overall ORC system. The state space model is obtained from nonlinear equations of elements of ORC which are given and described. Because ORC is a multiple-input and multiple-output (MIMO) process, a loop pairing with minimum interactions is needed to be determined to obtain the optimal control structure. To make the best loop pairing decisions and to analyse the interactions of ORC, the non-square relative gain array (NRGA) and dynamic non-square relative gain array (DNRGA) methods are used. Approximated transfer functions are derived from Bode diagrams which are given by using definitions of DNRGA method. These transfer functions are used to get the optimal parameters of the control structure. The proposed control structure uses proportional and integral (PI) linear controllers. A given control performance of the proposed control structure is shown and analysed in a simulation.