The plate heat exchanger (PHE) is a strong nonlinear cascade process, where the input is the steam valve position and the outputs are the steam flow-rate of inner loop and the supply water temperature of outer loop. In general the PHE operation is subjected to the large random disturbances caused by the outdoor temperature and the water randomly discharged by users. These disturbances will make the temperature and the flow rate of return water fluctuate a lot. This causes the supply water temperature to fluctuate outside the targeted range and leads to the frequently changes of steam flow-rate. To solve this problem, an intelligent cascade control method for the temperature interval of PHE is proposed for such a nonlinear process. The proposed method combines a feed forward compensation, a range limitation unit, rule base reasoning (RBR) and cascade control together. The intelligent control for the intervals of supply temperature method is established that includes a PI-based feed forward control for the supply water and a PI-based upper bound constraint control for the steam flow. The successful application to a real PHE confirms the effectiveness of the proposed method. In particular, the real application has shown that the proposed method can ensure the supply temperature to be within its technically specified range and can realize a small fluctuation range of steam flow-rate when the system is subjected to the disturbances of outdoor temperature and the randomly discharged water by users.
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