Research On Temperature Optimization And Predictive Control Of Microwave Heating Process

Microwave is a kind of electromagnetic wave in a specific frequency band.As a clean and efficient new energy,it has been widely used in chemical,biological,metallurgical,and food industries.Microwave heating has the advantages of fast heating speed,energy saving,selective heating,and easy control,which makes it more efficient than traditional contact heating or radiant heating methods based on fire,electricity,steam,etc.However,due to the uneven distribution of microwave electromagnetic fields,microwave heating also has the phenomenon of uneven temperature distribution of the material being heated,and local hot spots may occur.Therefore,the main points to improve the uniformity of material temperature during microwave heating are: 1.strict Control the rate of temperature rise at the highest temperature of the material;2.Change the microwave electromagnetic field distribution so that the material can absorb microwave energy as evenly as possible.In this paper,multi-feed microwave heating of solid particulate minerals is taken as the research object,and the improvement of the temperature uniformity of materials in the microwave heating process is the main purpose,taking into account the economic benefits of the multi-source microwave heating process.Based on the key points of improving the temperature uniformity of materials in microwave heating process,the increase of the number of microwave feeds is taken as the means to improve the temperature uniformity of materials in microwave heating process.The model predictive control method and the double-layer structure predictive control method are used to complete the following work by combining theoretical analysis,numerical calculation and computer simulation:(1)Combined with the characteristics of microwave heating,the model predictive control method is used to track and control the highest temperature of the microwave heating process with the highest temperature of the material as the controlled variable and the input microwave power as the manipulate variable;The weighting selection method of dynamic matrix is designed to overcome the adverse effects caused by the nonlinear characteristics in the microwave heating process,and the constraints adjustment method is designed to dynamically adjust the input microwave power to improve the heating rate of materials.Through computer simulation,the application of the model predictive control method can achieve the accurate tracking result of the highest temperature of the material to the target temperature,and after the application of the constraint adjustment method,the highest temperature of the material can reach the target temperature about 900 s in advance,which improves the efficiency of the microwave heating process,and effectively realizes the above-mentioned key point 1 for improve the temperature uniformity of the material in the microwave heating process.(2)Based on the premise that the microwave heating process has reached a steady state,the steady-state target calculation is introduced on the basis of the dynamic predictive control to form a double-layer structure predictive control method.In the steady-state target calculation,the expected target,constraint conditions,economic benefits and other factors for the purpose of improving the temperature uniformity of materials are considered comprehensively.An objective function is set to improve the economic benefits.The optimal steady-state target of input electric power of magnetron and material temperature is calculated within the constraints.In the dynamic predictive control,the input power of each magnetron and the temperature of each temperature measurement point are controlled to track the optimal steady-state target under the restriction of the constraints.Through the computer simulation of a 2-input-2-output microwave heating process,it is concluded that the economic optimization function of steady-state target calculation can increase 10.143 economic benefits for the process;after setting the expected target of each temperature measurement point as 105 ?,the temperature of each temperature measurement point can be close to the expected target,and the above-mentioned key point 2 to improve the material temperature uniformity in the microwave heating process is effectively realized.Compared with the traditional PID control,the double-layer structure predictive control can effectively eliminate the overshoot of the process and ensure the smoothness of the temperature change.