Constant pressure water supply automatic device designed for micro-irrigation system based on solar energy

Abstract: The stability of micro-irrigation system inlet water pressure affects the uniformity of the micro-irrigation and the mixed fertilizer accuracy of automatic fertilizer mixing device. In order to provide a constant inlet water pressure for small and medium-sized irrigation pipe network which adopts gravity drip irrigation, a constant pressure water supply automatic control device was developed, through employing a diaphragm pump DP-60 powered by solar energy to carry water to the reservoir built in high place, and maintaining the reservoir' water level at a fixed height in the drip irrigation process. The water level was detected online by using a level sensor YZ-YO-LAG1, and the controller control DP-60 carrying water to the reservoir according to the water level detected. Due to the certain distance between reservoir water level detection terminal and DP-60 control terminal, two wireless communication modules CC1100 were installed in each terminal respectively to realize wireless data transmission and control between two terminals. To reduce power consumption of wireless communication, a regular communication strategy combining with sleeping mechanism was adopted, and a kind of time synchronization technology was employed to keep time synchronization between the communication parties, and the WOR (wake on radio) mode of CC1100 module was enabled while communicating, the communication success rate was 100% verified by practical test. Photovoltaic capacity of the system had been designed for obtaining an optimal capacity combination of solar cell array and lead-acid battery, and the solar panel power was determined to be 60 W and the battery capacity to be 60 A·h, the capacity combination could meet the electricity demand of 500L irrigation norm for each drip irrigation cycle, and ensure that the system operates normally in seven consecutive days without sunshine. In order to maximize the use of solar energy, the relationship between solar panel power and the output frequency of solar radiation sensor TSL230 was calibrated through experiment, and then the controller could select the battery or solar panel as the direct power for DP-60 automatically, based on actual output power (obtained from the output frequency of TSL230) of the solar panel and the stage of charge of battery. To guide the application and installation of DP-60 in actual engineering, the maximum pumping head, maximum suction head, current characteristics and flow characteristics of DP-60 had been determined by experiments, with its inlet and outlet connecting with a PVC pipe of DN15 diameter respectively. To avoid the large peak pulse current, a soft start-up control was applied to control DP-60 by employing PWM (pulse width modulation) technology, and the frequency of PWM was 20 kHz, and the period for accomplishing a soft start or a soft stop was 2s. Practical application experiment for the constant pressure water supply automatic control device had been taken for more than 6 months, and the results showed the device was stable and the error of the reservoir water level was less than 1 cm.