基于PWM技术的大型变量喷灌机整机水力性能研究及优化

基于脉冲宽度调制（Pulse Width Modulation, PWM）技术的变量喷灌机虽然能实现更精细的地块水分管理,但因实现变量的电磁阀的持续开闭动作,喷灌机主输水管道内流量呈现持续的阶跃变化,进而导致变量喷灌过程中存在压力脉动和机械激振现象。该研究基于Matlab/Simulink,对基于PWM技术的大型变量喷灌机在变量喷灌过程中的压力脉动进行了研究分析及改善优化。针对已研制的基于PWM技术的大型变量喷灌机实体系统,首先构建了其关键器件和整机的水力模型,并验证了模型的正确性。然后基于所建模型,对变量喷灌机的压力脉动进行了分析,得到了变量喷灌过程中的压力脉动规律,进而提出了PWM脉冲相位错开的缓减方法,并介绍了该方法的3种具体实施方式,即"站间"错相、"站内"错相和"站间+站内"错相。最后在实现了PWM脉冲相位错开的变量喷灌机整机水力模型上进行仿真分析,证明了所提3种错相方式均可明显减小变量喷灌过程中的压力脉动幅度,同时也可有效提高泵站的利用率。此外,通过在实现了PWM脉冲相位错开的变量喷灌机实体系统上开展田间试验,进一步验证了所提PWM脉冲相位错开方法对于缓减压力脉动和机械激振的有效性。且田间试验结果表明,在采用PWM脉冲相位错开方法时,变量喷灌机仍然具有较好的喷洒均匀性和变量灌溉控制误差。该研究成果不仅能为基于PWM技术的变量喷灌提供较平稳的压力条件从而保障变量喷灌控制精度,还能减小因压力脉动引起的机架激振从而保障设备安全。

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.