Abstract: This paper presents a mixed method for finding stable reduced order models using error minimization technique and modified pole clustering technique for single input-single output (SISO) large scale systems. The denominator polynomial of the reduced order model is determined by forming the clusters of the poles of original system and the cluster centers are identified by using inverse distance measure criterion and the numerator polynomial is obtained by the error minimization technique. This reduced system with PID is stable even when the original high order system is unstable.

Keywords: Modified pole clustering, Order reduction, Error minimization technique, Stability, Transfer function