A closed-loop subspace identification method for continuous-time systems based on δ-operator model

This paper is concerned with a subspace identification of a continuous-time plant operating in closed-loop in the framework of the joint input-output approach. The main procedure consists of two steps. Firstly, the dual-Youla parametrization of the plant is used for obtaining an equivalent open-loop problem to the original closed-loop identification problem. Then, a delta-operator based IV-MOESP type subspace identification algorithm is developed to estimate the state space model for the joint input-output process, whereby a higher-order state space model of the plant is obtained by an algebraic operation. Subsequently, a model reduction procedure is employed to derive a lower-order plant model removing irrelevant modes from the higher order model. Simulation results by using numerical and chemical plant models demonstrate the feasibility of the proposed method.