Clara-Mihaela Ionescu

A MATLAB Interactive Tool for Computer Aided Control Systems Design in Frequency Domain: FRTool

Looking back at the history of control engineering, one finds that technology and ideas combine themselves until they reach a successful result, over the timeline of several decades (Bernstein, 2002). Simple dynamical compensators (such as PID, Phase-Lead, Phase-Lag, etc) have done in the past a remarkably good and efficient job in real-life control applications. Theoretical insight in the closed-loop behavior is provided by powerful and well-developed theories – which are considered as basic knowledge for every control engineer – such as the Root Locus and the Frequency Response techniques. In the past, these theories have been extensively used as analysis tools – e.g. the stability analysis of a given control system based on closed loop poles (Root Locus RL) or Nyquist criterion (Frequency Response FR). However, analysis implies that a controller is already available, irrespective of its design method. Nowadays, thanks to the computational and graphical power of modern computers, many of these theories can be implemented as interactive graphical design tools. In this way, control engineering moves away from being an abstract and mathematical-oriented discipline and it evolves gradually towards a mature engineering discipline. An extensive reflection upon the role of information science in control engineering has been given in (Dormido, 2004). This new way of interactive control education provides practical insights into control systems fundamentals (Wittenmark et al, 1998; Dormido et al, 2002). Such combinations of interactive environment and animation bring visualization to a new level and aid learning and active participation by control engineering students (Kheir et al, 1996; Johansson et al, 1998). Recently, a Root Locus RL toolbox has been introduced in Matlab – in this chapter, a Frequency Response toolbox (FRtool) will be presented. Although some other computer aided design (CAD) tools based on frequency response have been developed in the past (Balakrihsnan & Boyd, 1994; Satoh et al, 1994; Piguet & Gillet, 1997; Pouliz & Pouliezos, 1997; Piguet et al, 1999), the one presented in this contribution is highly interactive, graphical, easy-to-use and posing an elegant simplicity (especially for non-experts, as limited control engineering insight is required). The Matlab® controller design tool based on the root locus method (rltool) cannot handle systems with time-delay without approximating the dead5