Modern Control System Theory and Design, 2nd Edition

5.9.  OTHER PRACTICAL CONSIDERATIONS

The control engineer must be concerned with several other practical aspects before becoming able to state intelligently and completely the expected system performance. The concluding section of this chapter quantitatively discusses considerations of feedback system bandwidth, nonlinearities, size, weight, power consumption, and economics. Hopefully, this will aid in giving the reader a complete overall view of the problem.

Feedback system bandwidth is usually defined as the frequency at which the open-loop magnitude equals unity. Sometimes it is defined where it is −3 dB. The bandwidth of a system is indicated by its particular application. Usually, the control engineer is interested in designing the system to respond to a certain spectrum of input signal frequencies and to suppress all inputs above a certain frequency. It is important to emphasize that we should not arbitrarily design for a large bandwidth. Although large bandwidths usually result in large error constants, with small resulting system error, they also result in a system that responds to extraneous noise inputs and has considerable jitter due to the noise. The desirable approach is to design the feedback system bandwidth to be just large enough to pass the desired input-signal ...