Simple model reduction technique for transfer function models

In this work, a novel model reduction method is proposed for transfer function models. The method is based on equating the ratio of the coefficients of the 's', powers of 's' in the numerator to the corresponding coefficients of the s, powers of 's' in the denominator of the closed-loop transfer function of the higher order process to the closed-loop transfer function of the reduced order model with PI controlling settings. Using this method, a stable higher order process is reduced to a first-order plus time delay (FOPTD) model. The step response of the closed loop of the reduced order model is compared with the corresponding higher order process. The efficiency of the proposed method is shown for several examples and for the experimental temperature control process. By the proposed reduction method for higher order processes without zero, the reduced model time constant is simply written with the addition of the all time constants of the higher order process.