Page - 172 - in Adaptive and Intelligent Temperature Control of Microwave Heating Systems with Multiple Sources

5. ExperimentalResults 0 5 0 0 1 0 0 0 1 5 0 0 2 0 0 0 2 5 0 00 5 1 0 1 5 2 0 T i m e ( s ) P I DL i n e a r M P CN o n l i n e a r M P C (d)Standarddeviationwithrespect to the target temperature. Figure5.30. Control performance of PID, linear MPC and nonlinear MPC in the second setup. Due to slightly different duration in the three experiments, the comparison of standard deviation lasts until 2760s. not have the flexibility to deal with fast varying effects from the ther- malconduction,andthiskindofinfluenceisfurthertransmittedtothe estimation error of the heating effect. Using the setup 5.29, the cool- ing effect of each workpiece is more stable than the first setup, and correspondingly theaccuracyof thenonlinearsystemidentification is higher than the case with the first setup. Consequently, the final con- trolperformance is improved. In figure 5.30c, when the target temperature is increasing from 75◦C to100◦C, therearethreecontrolaccidentsoccurredconsecutively. Due to these three accidents, the controlled temperatures fail to follow the target temperature curve and the standard deviation becomes much larger than the normal level (from 1600 s to 1800 s). But after that period, the system estimator takes a short time to recover from the accidents and the control behavior is back to normal quickly. It also 172