The article presents a general synthesis method of controllers in the cascade system. At first, it determines structure for each of equivalent control loops in the cascade system and imposes robust conditions for these loops. | Journal of Automation and Control Engineering Vol. 4, No. 2, April 2016 A Synthesis Method of Robust Cascade Control System Nguyen Van Manh and Vu Thu Diep Department of Automation and Control of Thermal Processes, Hanoi University of Science and Technology, Vietnam Email: manhnv_2000@, Phan Duy Hung Department of Information Technology Specialization, FPT University, Vietnam Email: hungpd@ Abstract—The article presents a general synthesis method of controllers in the cascade system. At first, it determines structure for each of equivalent control loops in the cascade system and imposes robust conditions for these loops. After that, the structures of controllers in the system are defined. Then the proportional coefficients of controllers are retuned based on the “soft characteristic”. Finally, we show an example of using proposed method. II. A. The Viewpoint of High-Robust Control System [7] Let a control system has the transfer function: A( s) , where, s – complex variable; D(s) – the W (s) D( s ) characteristic polynomial with q real roots: si = – i and 2p pairs of conjugate-complex roots: sk k j k , k 0, Index Terms—cascade control system, soft characteristic, soft oscillation index I. j 1 ; q+2p = n; n – the order of D(s). Thereafter, we call roots of the polynomial symply characteristic roots. Let acting step input with Laplace transform: z(s) = 1/s. Our purpose is to construct robust control system therefore we consider only stable ones. So, the output system response can be written in the form: INTRODUCTION The cascade control is one of the most popular structures to improve performance of the single-loop control systems, by that arose the cascade control system. In the published works [1] [2] [3] [4] [5] [6], the authors deal with various concepts of a cascade control system. However, there is no identical view of cascade control system among them. The authors give some cascade structure .
