Page 260 - Modern Control Systems

CHAPTER Feedback Control System
4 Characteristics

4.1 Introduction 235
4.2 Error Signal Analysis 237
4.3 Sensitivity of Control Systems to Parameter Variations 239
4.4 Disturbance Signals in a Feedback Control System 242
4.5 Control of the Transient Response 247
4.6 Steady-State Error 250
4.7 The Cost of Feedback 253
4.8 Design Examples 254
4.9 Control System Characteristics Using Control Design Software 268
4.10 Sequential Design Example: Disk Drive Read System 273
4.11 Summary 277

PREVIEW
In this chapter, we explore the role of error signals to characterize feedback control
system performance. The areas of interest include the reduction of sensitivity to
model uncertainties, disturbance rejection, measurement noise attenuation, steady-
state errors and transient response characteristics. The error signal is used to control
the process by negative feedback. Generally speaking, the goal is to minimize the
error signal. We discuss the sensitivity of a system to parameter changes, since it is
desirable to minimize the effects of parameter variations and uncertainties. We also
wish to diminish the effect of unwanted disturbances and measurement noise on the
ability of the system to track a desired input. We then describe the transient and
steady-state performance of a feedback system and show how this performance can
be readily improved with feedback. Of course, the benefits of a control system come
with an attendant cost. The chapter concludes with a system performance analysis of
the Sequential Design Example: Disk Drive Read System.

DESIRED OUTCOMES

Upon completion of Chapter 4, students should:
Q Be aware of the central role of error signals in analysis of control systems.
Q Recognize the improvements afforded by feedback control in reducing system
sensitivity to parameter changes, disturbance rejection, and measurement noise
attenuation.
G Understand the differences between controlling the transient response and the steady-
state response of a system.
G Have a sense of the benefits and costs of feedback in the control design process.

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