A combined time and frequency domain method for model reduction of discrete systems |
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| Authors: | Chyi Hwang Yen-Ping Shih Ruey-Yinn Hwang |
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| Institution: | Department of Chemical Engineering, National Cheng Kung University, Tainan, Taiwan, People''s Republic of China;Department of Electrical Engineering, National Cheng Kung University, Tainan, Taiwan, People''s Republic of China |
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| Abstract: | A new combined time and frequency domain method for the model reduction of discrete systems in z-transfer function is presented. First, the z-transfer functions are transformed into the w-domain by the bilinear transformation, z = (1+w)/(1?w). Then, four model reduction methods—Routh approximation, Hurwitz polynomial approxima- tion, stability equation, and retaining dominant poles—are used respectively to reduce the order of the denominator polynomials in the w-domain. Least squares estimate is then used to find the optimal coefficients in the numerator polynomials of the reduced models so that the unit step response errors are reduced to a minimum. The advantages of the proposed method are that both frequency domain and time domain characteristics of the original systems can be preserved in the reduced models, and the reduced models are always stable provided the original models are stable. |
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