【摘要】 针对精准施肥机营养液的pH值调节过程控制本质非线性、时滞性、时变性、不确定性等特点,建立了描述该过程的数学模型。利用云模型能够处理定性概念和定量描述之间不确定转换的特点,提出了一种基于云模型推理的变论域模糊PI控制(CVFPI)算法。该算法采用正态云模型描述系统误差和误差变化率的语言值,通过X条件隶属云和Y条件隶属云分别实现规则前件和规则后件的推理,利用伸缩因子实时调整输入输出变量论域,由二维云推理机实现控制参数的在线修正。为验证该算法的有效性和优越性,分别对CVFPI、VFPI、PI等3种控制算法进行了仿真测试和田间试验。试验结果表明,提出的CVFPI控制算法能够适应精准施肥pH值调节过程的控制要求,相比于常规PI控制算法和VFPI控制算法,在不同工作点条件下超调量分别减小45.3%、21.2%,均方根误差分别减小54.9%、52.9%,在不同流量条件下超调量分别减小59.0%、48.4%,均方根误差分别减小54.1%、37.9%,具有较好的动态特性和稳态特性。更多还原

【Abstract】 The p H value regulating control process has the characteristics of nonlinearity, pure hysteresis,time degeneration and uncertainty in the precision fertigation system. A model described the p H value regulating process was established. The cloud model is a model that can deal with the uncertain transition between qualitative concepts and quantitative description. Based on this,a control algorithm with cloud inference in the variable universe fuzzy-PI controller( CVFPI) was proposed. In this algorithm,the normal cloud model was used to describe certain language concept corresponding to the system error and error rate. The inference of rule premise was realized by X conditional membership cloud while the inference of rule post was realized Y conditional membership cloud. A set of stretching factors with proportional exponential function was used to modify the universe of input and output variable real time,and a two dimensional inference engine based on cloud model was designed to adjust control parameters of PI controller on line. In order to verify the effectiveness and superiority of the proposed algorithm,the test platform of p H control process of the fertigation equipment was constructed. Two simulation experiments and two field experiments were carried out using CVFPI,VFPI and PI control algorithm respectively. The contrast testing results demonstrate that the proposed CVFPI control algorithm can meet the requirements of p H process control in the precision fertigation system,it has bettercharacteristics both in dynamic process and steady state. Compared to PI and VFPI,CVFPI has smaller overshoot,shorter stable time and stronger ability of anti-interference.更多还原