Optimum cascade PID controller design for SISO systems

The paper has presented two methods to determine cascade PID controller parameters for a SISO system. When the transfer function of a process is known, the optimization procedure can be used to tune the cascade controller for the given process. From the examples considered, it can be seen that the method usually results in a good closed-loop performance with small overshoot and short settling time for both tuning methods. The performance obtained when determining the controller settings by individual optimisations for each loop is often not far from the true optimum and normally produces satisfactory results. The auto-tuning method can also provide good tuning when the PID controller parameters are tuned by the use of formulae previously proposed by the authors (1993). The advantage of this approach is that it can be used when no mathematical model is available for the process.