Page - 163 - in Adaptive and Intelligent Temperature Control of Microwave Heating Systems with Multiple Sources

5.3. ResultsofDifferentControlMethods 0 5 0 0 1 0 0 0 1 5 0 0 2 0 0 0 2 5 0 02 0 4 0 6 0 8 0 1 0 0 1 2 0 DT2 = 1 6 ° C T a r g e tT 1T 2T 3T 4T 5 T i m e ( s ) DT1 = 1 2 ° C 0 2 0 4 0 6 0 8 0 1 0 0 Figure5.24. Control performance of PID control method (old cavity 3, 36 sources). ModelPredictiveControl Besides the PID control method, all other adaptive control methods introduced in this dissertation have also been tested. In the tests of the MPC methods, the control period is ∆t= 1.5 s and the prediction length isp= 5. In theory, the prediction length should be defined as large as possible, because a large prediction length normally leads to a better control performance [Wan09] [CA13]. But in practice, a large prediction length is not affordable because of the increased compu- tation time, especially for the nonlinear MPC. In order to keep a fast control pace (1.5 s), the prediction length is set to be 5 in our experi- ments. TheperformanceofthelinearandthenonlinearMPCmethods areshowninfigures 5.25. The two dashed lines in figure 5.25a are used to denote the control ’accident’ occurred in the heating process, such as in figure 5.26. In HEPHAISTOS, to guarantee the reliability of the whole system, a ex- ternal watchdog timer [Mur00] is equipped as a hardware switch to the power supplies. During the normal operation, the LabVIEW con- 163