施肥播种机肥料流量分段式PID控制系统设计与试验

Design and Test of Fertilizer Flow Piecewise PID Control System of Fertilizer Planter

施肥稳定性是评价变量施肥系统性能的重要指标,针对常规外槽轮式排肥器排肥时脉动性明显导致排肥均匀性差的问题,提出了基于肥料流量反馈的分段式PID控制方法,并设计了施肥播种机高精度肥料流量控制系统,系统采用肥料流量检测模块获取实时肥料流量并作为反馈输入,结合目标肥料流量,根据分段式PID控制算法得到控制输出量,驱动施肥电机,实现肥料流量的准确控制。搭建了施肥试验台,进行了肥料流量变化阶跃响应与施肥精度的台架试验,结果表明,肥料流量控制系统的阶跃响应时间最大值为1.42 s,均值为0.98 s,超调量最大值为3.49%,均值为2.82%,稳态误差最大值为0.89%,均值为0.64%,施肥量控制精度最小值为97.83%,均值为98.14%。在不同试验条件下,肥料流量控制系统的肥料流量控制精度与施肥精度均优于恒定转速系统。田间试验表明,当车速为4、6、8 km/h时,肥料流量控制系统的施肥量控制精度分别为97.84%、97.78%和97.82%,施肥量控制精度平均值为97.81%,标准偏差为0.28%,能够满足高精度施肥需求。

Fertilization stability is an important index to evaluate the performance of variable rate fertilization system.In order to solve the problem that the precision of fertilization is reduced due to obvious fluctuation during fertilizer discharge with external trough wheel type fertilizer drainer.A piecewise PID control method using fertilizer flow rate as feedback value was proposed.And a high-precision fertilizer flow control system of fertilizer planter was designed.The system regarded the real-time fertilizer flow value collected by the fertilizer flow detection module as the feedback value of the fertilizer flow controller in the vehicle terminal.Controller calculated output based on target and real-time fertilizer flow,and sent to fertilizer motor through USB to CAN module.Accurate control of fertilizer flow rate was realized.Fertilizer application test stand was built.Mathematical model between fertilizer and accumulative value of capacitance was established and validated.The results showed that the maximum measurement error of sensor was 1.20% when using this model,which met the requirement of fertilizer flow detection.Indoor bench test on response of fertilizer flow rate change and fertilization accuracy was carried out.The results showed that the response time of the fertilizer flow control system was 1.42 s,mean value was 0.98 s,maximum overshoot value was 3.49%,mean value was 2.82%,maximum steady-state error was 0.89%,mean value was 0.64%,minimum fertilization accuracy was 97.83%,and mean value was 98.14%.Under different test conditions,the accuracy of fertilizer flow control and fertilization of fertilizer flow control system was better than that of constant speed system.Field tests showed that at vehicle speeds of 4 km/h,6 km/h and 8 km/h,the accuracy of fertilizer application rate of fertilizer flow control system was 97.84%,97.78% and 97.82% respectively,and the average accuracy of fertilizer application rate was 97.81%,and the standard deviation was 0.28%,which met the requirements of fertilizer application accuracy of fertilizer system.