Page 44 - Modern Control Systems

Chapter 1 Introduction to Control Systems

designed devices and products. These uncertainties are embodied in the idea of un-
intended consequences or risk. The result is that designing a system is a risk-taking
activity.
Complexity, trade-off, gaps, and risk are inherent in designing new systems and
devices. Although they can be minimized by considering all the effects of a given de-
sign, they are always present in the design process.
Within engineering design, there is a fundamental difference between the two
major types of thinking that must take place: engineering analysis and synthesis.
Attention is focused on models of the physical systems that are analyzed to provide
insight and that indicate directions for improvement. On the other hand, synthesis is
the process by which these new physical configurations are created.
Design is a process that may proceed in many directions before the desired
one is found. It is a deliberate process by which a designer creates something new
in response to a recognized need while recognizing realistic constraints. The de-
sign process is inherently iterative—we must start somewhere! Successful engi-
neers learn to simplify complex systems appropriately for design and analysis
purposes. A gap between the complex physical system and the design model is in-
evitable. Design gaps are intrinsic in the progression from the initial concept to
the final product. We know intuitively that it is easier to improve an initial con-
cept incrementally than to try to create a final design at the start. In other words,
engineering design is not a linear process. It is an iterative, nonlinear, creative
process.
The main approach to the most effective engineering design is parameter analy-
sis and optimization. Parameter analysis is based on (1) identification of the key pa-
rameters, (2) generation of the system configuration, and (3) evaluation of how well
the configuration meets the needs. These three steps form an iterative loop. Once
the key parameters are identified and the configuration synthesized, the designer
can optimize the parameters. Typically, the designer strives to identify a limited set
of parameters to be adjusted.

1.5 CONTROL SYSTEM DESIGN

The design of control systems is a specific example of engineering design. The goal
of control engineering design is to obtain the configuration, specifications, and iden-
tification of the key parameters of a proposed system to meet an actual need.
The control system design process is illustrated in Figure 1.17. The design
process consists of seven main building blocks, which we arrange into three groups:
1. Establishment of goals and variables to be controlled, and definition of specifications
(metrics) against which to measure performance
2. System definition and modeling
3. Control system design and integrated system simulation and analysis

In each chapter of this book, we will highlight the connection between the de-
sign process illustrated in Figure 1.17 and the main topics of that chapter. The objec-
tive is to demonstrate different aspects of the design process through illustrative