Research and optimization of hydraulic characteristics of large-scale variable sprinkler irrigation machine based on PWM technology

Although the variable sprinkler irrigation machine based on pulse width modulation (PWM) technology can achieve more sophisticated water management in plots, the continuous opening and closing actions of the solenoid valve that realise variable rate irrigation make the flow rate of the main pipeline of the variable sprinkler irrigation machine a continuous and stepped change, which in turn leads to pressure pulsation and mechanical excitation in the variable sprinkler irrigation process. Based on Matlab/Simulink, the pressure pulsation of the large-scale variable sprinkler irrigation machine based on PWM technology in the variable sprinkler irrigation process was analyzed and improved. Regarding the developed large-scale variable sprinkler irrigation machine based on PWM technology, the hydraulic model of the key components and the whole machine were constructed first, and the correctness of the models were verified by experiments. Then based on the built hydraulic models of the whole machine, the pressure pulsation of the variable sprinkler machine was analyzed, and the law of the pressure pulsation in the variable sprinkler irrigation process was obtained. The results indicated that the amplitude of pressure pulsation had no effects on the duty cycle of the PWM pulse while was positively related to the operating pressure level of the system, the number of valves opened or closed at the same time, and the response time of the pressure adjustment of the water supply system. Furthermore, in order to reduce the number of valves that are opened or closed at the same time, the mitigation method of PWM pulse phase staggering was proposed, and three specific implementations of the method had been introduced, including staggering phase between stations, staggering phase in the station, and staggering phase between stations and within the station. Finally, the simulation analysis of the whole machine with implementing the PWM pulse phase staggering method on the model proved that three proposed staggering methods could significantly reduce the pressure pulsation amplitude in the variable sprinkler irrigation process, and also effectively improve the utilization rate of the pumping station. In particularly, the method that staggering phase between stations and within the station had the most obvious effectiveness on reducing pressure pulsation, which can reduce the maximum pressure pulsation amplitude from 0.60 MPa before phase staggering to 0.01 MPa. In addition, field experiments after realizing the PWM pulse phase staggering method on the developed large-scale variable sprinkler irrigation machine based on PWM technology further verify the effectiveness of the proposed PWM pulse phase staggering method in reducing pressure pulsation and mechanical excitation. The results in field experiment showed that the variable sprinkler irrigation machine still has good spray uniformity and variable irrigation control error when using the PWM phase staggering method. These research results can not only provide relatively stable pressure conditions for variable rate irrigation based on PWM technology to ensure the control accuracy in the variable sprinkler irrigation process, but also reduce the mechanical excitation caused by pressure pulsation to ensure the safety of the equipment.