A subspace system identification algorithm guaranteeing the negative imaginary property

The negative imaginary (NI) property occurs in many important applications. For instance, flexible structure systems with collocated force actuators and position sensors can be modeled as negative imaginary systems. Obtaining a mathematical model for this class of systems using system identification methods may result into inaccurate models that poorly reflect the negative imaginary property. In this paper, a modified subspace system identification algorithm that ensures the negative imaginary property is presented. As an application of these results, an example of modeling a flexible system with a piezoelectric actuator and position sensor is presented.