基于PWM技术的平移式变量喷灌机喷头流量分配方法

大型平移式喷灌机采用脉冲宽度调制(Pulse width modulation,PWM)技术实现变量灌溉作业,因喷头间喷洒区域相互重叠,由地块管理区的设计处方值求解单喷头流量较为困难。首先根据Nelson R3000型单喷头喷洒特性,得到平移式喷灌机沿桁架方向的一维叠加水量分布特性,以及平移运动后的二维叠加水量分布特性,分析确定了由4个喷头重叠喷洒控制一个管理区,并得到喷头区域喷洒分配率,在此基础上提出了按处方值进行喷头流量分配的加权均分法和基于遗传算法(Genetic algorithm,GA)的分配法。通过管理区喷洒误差分析得出,当相邻处方值变化幅度不超过最大处方值的33%时,精度可以达到5%。为了弥补GA法导致喷洒均匀性下降的不足,将加权均分法和GA法组合应用,有效降低了处方值突变带来的喷洒误差,同时保证了处方值变化较小区域的喷洒均匀性。本文方法可以扩展到4个以上喷头重叠喷洒控制一个管理区的应用场合。

Sprinkler Flow Rate Distribution Method in Lateral Moving Variable Rate Irrigation System Based on PWM

During the variable rate irrigation operation of large-sized lateral moving irrigation system based on pulse width modulation (PWM) technique, it is quite difficult to solve the flow rate of each sprinkler from the designed prescriptions of management zones because the spraying areas of sprinklers will overlap with each other. At the beginning, the overlapped water distribution in lateral direction, and the two-dimensional contour plot of overlapped water distribution were gotten based on the feature of single sprinkler water distribution of Nelson R3000. Then four sprinklers were determined to control a management zone and the water distribution rate of spraying area was solved. And on this basis a weighted average method and a genetic algorithm (GA) method based on genetic algorithm were proposed to perform sprinkler flow rate distribution according to the prescription. It was found that the solution accuracy can reach 5% when the change between adjacent prescriptions was less than 33% of the maximum prescription by analyzing the irrigation error in management zone. In order to make up for the reduction of irrigation uniformity caused by GA method, a combined method of weighted average method and GA method was put forward. Related examples had showed that the irrigation error caused by the saltation of adjacent prescriptions can be reduced by the combined method effectively and the irrigation uniformity of management zones where prescriptions changed little can also be guaranteed at the same time. By changing the mapping relationship between sprinkler flow rate and actual irrigation volume in each management zone, this method can be extended to more than four sprinklers controlling a management zone.