Understanding closed-loop identification with ITCLI

Prior work by the authors (featured in software sessions held during SYSID 2009 and 2012) described ITSIE and ITCRI, a series of interactive tools designed to aid students and practitioners in better understanding the role of design variables associated with classical prediction-error and control-relevant identification, respectively. This paper presents ITCLI (Interactive Tool for Closed-Loop Identification), an interactive software tool for understanding design variables in closed-loop identification of LTI SISO systems using prediction-error techniques. The tool enables an interactive evaluation regarding how bias and variance effects are manifested when identification is performed under closed-loop circumstances. The role of external signal design, choice of model structure, controller tuning during identification testing, and signal injection points (at either the manipulated variable or the setpoint) while in the presence of autocorrelated disturbances can be evaluated in a comprehensive and easy-to-operate tool. The software is developed using Sysquake and is provided as a stand-alone executable version in the Windows and Mac OS operating environments.