Study On Adaptive Control System Of Kelp Solar-Heat Pump Drying

Besides possessing valuable edible and medicinal values,kelp was also an important raw material in chemical and agricultural fields.Due to the characteristics of high moisture content,seasonality and concentrated production,drying of fresh kelp was an indispensable part of the kelp processing process.In response to the problems of long adjustment time,poor steady-state accuracy and high energy consumption in traditional kelp drying,this paper combined solar energy and heat pump drying technique and applied them to the kelp drying process,designed the adaptive control system of solar-heat pump drying,and realized real-time monitoring and self-adaptive regulation of the kelp drying process.The specific research work was as follows.Based on the principles and characteristics of solar drying technology,heat pump drying technology and solar-heat pump synergistic drying technology,this paper determined the mode of using the combination of greenhouse-type solar drying and air-source heat pump drying.The solarheat pump synergistic drying system was designed according to the drying demand of kelp,and the specific operation mode of the system was analyzed,and the solar-alone drying mode,heat pump-alone drying mode and solar-heat pump synergistic drying mode were constructed to meet the demand of all-weather drying operation of kelp.The first-order inertia link transfer function with delay was established for the structural parameters of greenhouse-type solar drying chamber.The fuzzy logic toolbox of MATLAB software was used to design a fuzzy controller with the structure of "two-dimensional input and one-dimensional output",and the Simulink platform was used to simulate and analyze the drying chamber transfer function as the control object.The final steady-state error was maintained within±3? without over-tuning.The software and hardware of the control system were designed and developed.The Siemens S7-1200 PLC was selected as the processor for the control system,and the KTP 700 Basic PN touch screen was used for human-machine interaction.The EPLAN software was used to design the control system power distribution diagram and PLC wiring diagram,and the physical wiring and hardware platform were built according to the electrical design drawings.In addition,the software design of the control system was carried out with the help of Siemens-TIA Portal,and the self-adaptive control system of solar-heat pump drying including the main program module,data acquisition module and execution module was designed with the modular design idea.In addition,a human-machine interface with multi-level menu structure was designed to realize functions such as environmental data acquisition and real-time monitoring of equipment operation status during the drying process.A no-load verification test was conducted on the solar-heat pump cooperative drying system,and the target temperature of the drying chamber was set at 40°C.The results showed that the system took about 20 min to dry the preheating stage,the overshoot was about 3.03%,and the steady-state error was about 1.21°C.The temperature control effect was good and could meet the temperature requirements of kelp drying.The solar energy alone,the heat pump alone and the solar-heat pump cooperative drying tests were conducted with the kelp as the drying object.The test showed that the temperature fluctuation range became larger and the temperature extreme difference became larger as the setting temperature increased;the maximum average error of temperature was 1.84? under different setting temperature conditions,and the maximum temperature deviation was within ±5?.The average error of drying room temperature under different weather conditions was ±2?.For drying a batch of kelp,the solar energy alone used the least amount of electricity,but the target moisture content could be reached only under sunny conditions,which took about 7 h.The heat pump alone used the most electricity,which was 19.73 kW·h.Under sunny conditions,the drying time of the solar-heat pump cooperative drying was shortened by 3 h compared with the solar energy alone,and the energy consumption was reduced by 27.14% compared with the heat pump alone.The dried kelp dried by solar-heat pump was better than traditional drying in terms of color and morphology,and the character was better.