In this paper, the settling time of closed-loop systems controlled with PID, which is established by using magnitude and symmetric optimum methods, is analyzed. These methods have some limitations such as limited frequency bands, existence of overshoot and larger settling time. | Vietnam Journal of Science and Technology 55 (3) (2017) 357-367 DOI: SETTLING TIME ASSIGNMENT WITH PID Nguyen Doan Phuoc, Nguyen Hoai Nam Hanoi University of Science and Technology, 1 Dai Co Viet Street, Hanoi * Email: Received: 24 October 2016; Accepted for publication: 21 February 2017 ABSTRACT In this paper, the settling time of closed-loop systems controlled with PID, which is established by using magnitude and symmetric optimum methods, is analyzed. These methods have some limitations such as limited frequency bands, existence of overshoot and larger settling time. Thus, our aim is to improve these performances of the closedloop system for a certain class of transfer functions. The proposed method will be tested on a DC motor by simulation. It can be concluded that the method provides a larger range of frequency, smaller settling time and no overshoot. Keywords: PID controller, magnitude optimum criterion, symmetric optimum criterion, firstorder system, first-order plus integral system. 1. INTRODUCTION Many PID tuning methods have been developed since 1940s. These methods can be classified into groups: practical approach [1 - 4]; optimal approach [5 - 8]; gain and phase margin specification based approach [9 - 13] and others [14 - 18]. However, there have not been yet any method that concurrently dealing with both the settling time and the overshoot of the closed-loop system. It is known that when plants, having transfer functions of first-order, second-order and third-order systems the magnitude optimum method based parameter determination k p , TI and TD [5 - 8] for the PID controller seems to be one of the most effective methods, validated in reality. However, there has been no fundament until now to conclude that the magnitude optimum method is the only one to provide PID controller parameters to make the closed-loop system stable and the settling time short in the sense that the closed-loop .
