A Study On Temperature Control Based On Multirate Adaptive Control In Microwave Heating Process

Compared with the traditional heating,the method of microwave volume heating offers several advantages,including non-pollution,alternative heating,shorter processing,faster start-up speed and so on.And it has some successful applications in the industrial,agricultural and medical fields.However,the dielectric material under microwave radiation exist the phenomena of temperature distribution non-uniformity and local overheating,which may lead to some safety problems like thermal runaway.The main measure to solve or improve these problems is to control the temperature or temperature rising rate of heated material effectively.Since the characteristic of volume heating and rapid heating,and the system of time-varying,external disturbance and internal uncertainty,it is difficult to control the material's temperature accurately and real-timely control in the microwave heating process.Therefore,this dissertation aims to prevent thermal runaway and improve non-uniform temperature distribution,after comprehensive analysis for the microwave heating principle,characteristics and basic components of the system,two kinds of multirate adaptive control strategy are adopted to control single-point and multi-point temperature,respectively.And the main contents are as follows:(1)In order to achieve the objective of preventing thermal runaway,and considering the situation that the rate of input microwave power is faster than the temperature detection period,an SISO multirate adaptive control strategy is proposed to track the maximum temperature in multiple temperature detection points by controlling the microwave power quickly and accurately.In this control strategy,an internal model filter is introduced to simplify the tracking problem into the stability problem.And the adaptive output estimator is applied to identify the multirate system.Then,considering the system's asymmetric saturation input constraint,the adaptive algorithm based on ASPR condition is improved,and its effectiveness is verified by simulation and experiment.(2)Focusing on improving the temperature distribution non-uniformity,the SIMO multi-rate adaptive control strategy is then proposed to control multi-point temperature effectively.In this control strategy,the tracking control problem of the SIMO system is transformed to the stability of square MIMO system by multi-rate sampling and internal model filter,thus facilitating the design of adaptive controller.Further,taking into account the input constraint problem,an improved adaptive control algorithm is proposed,and its stability is proved by the Lyapunov second method.Finally,the effectiveness of this control strategy in improving the temperature distribution uniformity is analyzed by simulation.