10.4. Cascade-Control Design
Tuning the cascade controller consists of two steps. First, tune the inner-loop controller [gc2(s)] based on the secondary process [gp2(s)] and use the inner-loop/closed-loop transfer function [Equation (10.2)] to find an effective process transfer function [Equation(10.4)] for tuning the outer-loop controller [gc1(s)].
The inner-loop control system design can be based on IMC-based PID or any other procedure, such as frequency-response gain and phase margins. Once the inner-loop is tuned, the effective outer-loop transfer function can be used to tune the outer-loop controller. Again, any control design procedure can be used.
Figure 10-9. Series cascade structure using a closed-loop transfer function for the inner-loop. ...
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