Abstract:Engineers are sometimes asked to analyze the feasibility of existing control systems or design a new system. The conventional analysis and design methods heavily depend on mathematical calculation. In order to minimize calculation, graphical control is proposed. This paper aims to introduce three different graphical control tools (Root Locus, Bode diagram and Nyquist diagram) and then use these tools to analyze and design the control system. Finally, some realistic case studies are used to compare the advantages and disadvantages of graphical tools. The innovation of this paper is adding hand-drawn graphical control to greatly reduce the calculation complexity
List of SymbolsTs-settling time (s) -damping ratio n -natural frequency (rad.s -1) %OS-percentage of overshoot Ess-steady state error K-gain of the system Z 1 , Z 2 -zeros of the system P 1 , P 2 -poles of the system T p -peak time (s) M-magnitude of the phasor Φ-phase angle of phasor (degrees) Θ-angle of asymptote Z-the number of closed loop poles P-the number of open-loop poles Nthe number of counter clockwise rotation P M -phase margin (degrees) G M -gain margin h 1 , h 2 -feedback coefficient
IntroductionClassical control theory, modern control theory and robust control theory are commonly used today. In advanced engineering and science, automatic control plays a very important role. There are many applications using control systems: examples include rocket firing systems, splashing cooling water systems and car engine systems. Control theory is becoming incredibly important in daily life.
[1][2]It is now well known the response of closed-loop system is much faster than the open-loop. Thus more mathematical methods were developed to solve the closed-loop control, however they are not straightforward. [3] A system's performance will be greatly influenced by the position of the poles, especially by a pair of dominant poles. Since conventional mathematical techniques are too complex to effectively analyze the system, new graphical methods have been proposed to analyze the performance of control system. [4] In [5], Kinnen proposes a graphical control method to control multivariable control systems, a significant breakthrough in the control area. Compared with the traditional method (utilizing matrix formulation), the calculation is greatly reduced. In [6] O'Brien attempts to design a discrete control system, simply based on the Root Locus method. In [7], Koenig worked on analyzing a system's frequency response and then determining the stability of the control system using a Bode diagram. In This paper focusses on an improved process to design the system in a simple way and analyze which graphical technique should be used in different cases.