Design of fuzzy control system for orchard frost protection wind machine and experiments of frost protection effect

Abstract: In order to prevent the frost damage of fruit trees and improve the management method in orchard, an orchard frost protection wind machine and control method based on fuzzy control was designed in this paper. The control system contained micro controller STM32, temperature and wind speed sensors, touch screen, inverter and power supply device. Temperature and wind speed sensors collect the environmental information and transmit data through wireless radio frequency network. The touch screen displays the environmental status information, users can set temperature values to control the wind machine automatically. An axial fan was installed on the rotation device as the air supply system, the diameter of the fan is 900 mm, and the motor power is 4 kW. The fan is located at the height of 9.5 m with tilt angle 20°. The effective distance of frost protection wind machine is 5-48 m, and the rotation device drives the fan to sweep with angle of 360°, the maximum protection area of the wind machine is about 7 150 m2. An intelligent frost protection strategy based on fuzzy control with dual input and single output was designed. The 2 input variables are inversion temperature difference and temperature difference rate respectively, the output variable is rotation speed changes rate of wind machine. Due to the limitition of weather conditions and test site, the suitable test days are few, and the occurrence time of frost with inversion temperature is short. Frost protection effect tests were conducted in a Fuji apple orchard. The total area of the orchard is 6 000 m2, and the apple trees are planted with row spacing 4 m and plant spacing 2 m. The frost protection effect of the fuzzy control and the basic control was tested on frost nights in March and April, 2018. The test results showed that the rotation speed and the distance from the wind machine have interaction effects. Under fuzzy control mode, the average wind speed and temperature drop range were less than that of the basic control mode, and the maximum differences were about 0.5 m/s and 0.2 ℃ respectively. With the increase of the distance from the frost protection wind machine, the temperature drop range increased. The average temperature rise in the working area was 3.1 ℃ under fuzzy control mode, which was higher than that of basic control mode of 2.8 ℃. The temperature distribution under fuzzy control was more uniform, and the operation time was saved by 21.1% compared with the basic control. Under the 2 control modes, the frost damage rate of apple tree buds was 5.6% and 11.6% respectively, the frost damage was reduced by 6% under fuzzy control, the frost protection effect under fuzzy control had a better performance. This study provides a reference for intelligent control of frost protection wind machine, but the performance of the wind machine still needs to be optimized.