Study And Application Of Cascade Control Based On H Infinity Optimal Sensitivity

The manufacture process in modern industry was more and more complex, especially in the process control fields such as petroleum and chemical industry. With the increments of the quality requirements in control system, the single-loop systems weren’t able to meet the requirements. Cascade control was a control system which could improve the performance of the traditional single-loop structure. The researches on the cascade control have been mainly focused on two aspects:one area is the tuning of two controllers. Due to the difference between two the controllers in cascade control structure, the tuning methods also had different options. Compared with a single-loop system, the tuning method for cascade control was also more complex. The other area of study was mainly focused on the optimization of traditional cascade control structure. For example, a cascade control structure combined with internal model control or Smith predictors, which could track input signals with no steady-state error and make compensation in time-delay systems.In this paper, an improved control system was proposed, based on the analysis of two areas in cascade control mentioned above. By using the IMC controller in the secondary loop, the quadric disturbance could be eliminated effectively and rapidly according to internal model control theory. Minimum sensitivity was used as the design criteria in the primary loop and the tuning parameters of the primary controller were obtained by H, optimal control theory. This two-degree-of-freedom control system could be simplified into the standard cascade control structure. Simulation research was done on a two-capacity-tank object. Compared with other cascade control algorithms, the results showed this algorithm provided a better performance in set-point tracking, load disturbance rejection and robustness etc.At last, the turning method proposed in this paper was embedded into the Global Script of WinCC by programming C function, and was applied on "THJFCS-1fieldbus system experimental device’" to control the level of two-tank process by using Siemens S7-300PLC. Real-time monitoring software WinCC was used to monitor the process. The experiment results showed that using this algorithm provided faster response speed, smaller overshoot, and better set point-tracking performance.