Modern Control System Theory and Design, 2nd Edition

7.10.  TRADEOFFS OF USING VARIOUS CASCADE-COMPENSATION METHODS AND MINOR-LOOP FEEDBACK

This chapter has presented the use of phase-lag, phase-lead, and phase-lag–lead cascade compensation networks, and minor-loop feedback, compensation (such as rate feedback). The question arises as to which compensation method should be used: cascade compensation or minor-loop feedback compensation. If the answer turns out to be cascade compensation, the question arises as to whether we should use phase-lag, phase-lead, or phase-lag–lead networks? This section addresses these reasonable questions by discussing the tradeoffs of these different methods of compensation, and guidelines are provided for the practical design of control systems.

I cannot provide a simple answer as to what compensation approach is the “best” method to use. Table 7.2 [11] compares the advantages and disadvantages of phase-lag, phase-lead, and phase-lag–lead networks, and minor-loop rate feedback for compensation. They are compared on the basis of characteristics, performance, applicability, and relative cost. Each of these four approaches will improve system stability if used properly, as shown in Chapters 6 and 7. Therefore, each system must be considered separately in order to determine the most effective, optimimum, or “best” approach.

If the system specification requires the need for a low-noise (“quiet”) control system ...