| 模糊与PI分段调控肥液EC的优化设计与试验 |
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| 引用本文： | 王海华,付强,孟繁佳,梅树立,王俊衡,李莉.模糊与PI分段调控肥液EC的优化设计与试验[J].农业工程学报,2016,32(15):110-116. |
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| 作者姓名： | 王海华 付强 孟繁佳 梅树立 王俊衡 李莉 |
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| 作者单位： | 1. 中国农业大学现代精细农业系统集成研究教育部重点实验室,北京100083;中国农业大学信息与电气工程学院,北京100083;2. 中国农业大学现代精细农业系统集成研究教育部重点实验室,北京,100083;3. 中国农业大学信息与电气工程学院,北京,100083 |
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| 基金项目： | 国家自然科学基金项目(31301240)；土壤植物及其系统技术国家重点实验室开放课题(2014-SKL-03) |
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| 摘 要： | 设施蔬菜生产中对肥液电导率(EC)的精量调控是实现智能灌溉的关键技术之一。肥液混合过程中,由于母液浓度、吸肥方式和灌溉流量等存在差异,试验检测到的EC值会产生滞后和不稳定现象。针对上述问题,本研究设计了一种通过测量频率间接得到肥液电导率的传感器,并以MSP430单片机为主控制器构建了一套水肥调控试验系统。同时,在肥液调控方法方面设计了粗细分段控制策略,控制方法均为以输出相应的占空比来控制吸肥电磁阀的开闭。当实测EC值与目标EC值相差较大时,采用PI控制方法,能够快速缩小差距;而当两者偏差较小时,采用模糊控制可以使混肥EC值逼近设定值。此外,试验利用多管路复合式文丘里,设计了4组不同的EC目标值和4种不同的吸肥管路组合进行吸肥测试。结果表明,EC传感器间接测量到的频率与实际肥液EC值有显著的线性关系,决定系数为0.999 5,保证了测试精度。当目标EC值设定为2 m S/cm时,分段控制情况下实测EC达到稳态的用时为122 s,最大EC值为2.34 m S/cm,优于采用单PI控制的180 s和2.62 m S/cm。且目标EC值越大,稳态EC值越精确,但是稳态时延和过量超调现象更明显。本研究表明分段调控能够较好地克服EC值的过量超调,同时混肥时间和实测EC值能够满足实际需求。
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| 关 键 词： | 温室 灌溉 传感器 模糊控制 PI控制 分段调控 水肥一体化 |
| 收稿时间： | 2015/3/14 0:00:00 |
| 修稿时间： | 2016/5/10 0:00:00 |
Optimal design and experiment of fertilizer EC regulation based on subsection control algorithm of fuzzy and PI |
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| Wang Haihu,Fu Qiang,Meng Fanji,Mei Shuli,Wang Junheng and Li Li.Optimal design and experiment of fertilizer EC regulation based on subsection control algorithm of fuzzy and PI[J].Transactions of the Chinese Society of Agricultural Engineering,2016,32(15):110-116. |
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| Authors: | Wang Haihu Fu Qiang Meng Fanji Mei Shuli Wang Junheng and Li Li |
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| Institution: | Key Laboratory on Modern Precision Agriculture System Integration Research of Ministry of Education, China Agricultural University, Beijing 100083, China;College of Electrical and Information, China Agricultural University, Beijing 100083, China,Key Laboratory on Modern Precision Agriculture System Integration Research of Ministry of Education, China Agricultural University, Beijing 100083, China,Key Laboratory on Modern Precision Agriculture System Integration Research of Ministry of Education, China Agricultural University, Beijing 100083, China,College of Electrical and Information, China Agricultural University, Beijing 100083, China,Key Laboratory on Modern Precision Agriculture System Integration Research of Ministry of Education, China Agricultural University, Beijing 100083, China and Key Laboratory on Modern Precision Agriculture System Integration Research of Ministry of Education, China Agricultural University, Beijing 100083, China |
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| Abstract: | Precise control of EC for fertilizer solution is one of the key technologies to realize smart irrigation in the production of protected vegetable.Serious lag and instability in EC detection will happen during the mixing of fertilizer and water due to differences in mother liquor concentration, fertilizer suction method and irrigation flow etc.To solve this problem, a new EC sensor was designed to measure the EC value of fertilizer solution indirectly by measuring the frequency based on different EC values leading to different equivalent resistances, and the smart irrigation system was developed as microcontroller (MSP430) was the master controller.Meanwhile, a subsection control strategy was introduced to regulate and control the EC value of fertilizer solution, and the opening or closing of electromagnetic valve for the suction of fertilizer solution was controlled by outputting corresponding duty cycle.When the difference between the target EC value and the measured value was large, PI control was adopted to narrow the gap as fast as possible.In this study, the threshold is defined as 0.2 mS/cm according to practical knowledge, therefore, fuzzy control with good robustness and high adaptability was adopted when the difference was smaller than 0.2 mS/cm.In fuzzy control stage, triangle function and centroid method were selected as membership function and defuzzification calculation with 63 rules and the output language variable value was divided into 13 levels.A compound venturi was designed as fertilizer solution suction device, with the diameter of inlet and outlet pipes was both 40 mm, and a closed-container (10 cm×10 cm×6 cm) was installed at the throat part to connect the inlet and outlet pipes, and 7 suction interface were located at the bottom of the container to link with the electromagnetic valves.The main pipe of the irrigation system was controlled by 24VDC electromagnetic valve and the drippers of the branch pipes were inserted into the substrate near plant roots.The filter was installed between inlet water and the irrigation system to avoid blocking venturi and drippers.An experiment including 4 different target EC values and 4 different suction pipelines was carried out to test the effect of the designed control system.The results showed that the frequency measured by our EC sensor had a significant linear correlation with the measured EC value with R2 is 0.999 5.In the case of subsection control, when the target EC value was 2 mS/cm, the steady response time was 122 s and maximum overshoot is 0.34 mS/cm when 4 channels were used for fertilizer solution suction, which performed much better than only PI control with steady response time 180 s and maximum overshoot up to 0.62 mS/cm.In addition, the higher the target EC value set, the more accurate the steady EC value was, however, the steady response time became longer and overshoot was more serious.The subsection control strategy used in this study can effectively overcome excessive overshoot, also the time for mixing fertilizer solution and the measured EC value can both meet the requirements for the practical production of protected vegetable. |
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| Keywords: | greenhouses irrigation sensors fuzzy control PI control subsection control integration of water and fertilizers |
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