毕业论文-PID温控系统的设计及仿真.doc

CENTRAL SOUTH UNIVERSITY
本科生毕业论文
题目
PID温控系统的设计及仿真
学生姓名
指导教师
学院
信息科学与工程学院
专业班级
完成时间
年月
摘要
温度是工业控制的主要被控参数之一。可是由于温度自身的一些特点,如惯性大,滞后现象严重,难以建立精确的数学模型等,给控制过程带来了难题。
要对温度进行控制,有很多方案可选。PID控制简单且容易实现,在大多数情况下能满足性能要求。模糊控制的鲁棒性好,无需知道被控对象的数学模型,且在快速性方面有着自己的优势。研究分析了PID控制和模糊控制的优缺点,把两者相互结合,采用了用模糊规则整定、两个参数的模糊自整定PID控制方法。本研究以电烤箱为控制对象,用MATLAB软件对PID控制、模糊控制和参数模糊自整定PID控制的控制性能分别进行了仿真研究。仿真结果表明PID对于对象模型复杂和模型难以确定的控制系统具有很大的局限性,不能满足调节时间短、超调小的技术要求。由于模糊控制的理论(如量化因子和比例因子的确定问题)并不完善,其可能获得的控制性能无法把握,而且模糊控制易受模糊规则有限等级的限制而引起稳态误差。参数模糊自整定PID控制吸收前两种方法的长处,满足了调节时间短、超调量为零且稳态误差较小的控制要求。因此本论文最终确定采用参数模糊自整定PID控制方案。
本系统硬件采用了以 AT89C52 单片机为核心的温度控制器,选用 k 型热电偶为温度传感器结合MAX6675芯片构成前向通道,同时双向晶闸管和SSR构成后向通道,由按键、LED 数码显示器及报警单元等组***机联系电路。
关键词:单片机,PID,模糊控制,仿真
ABSTRACT
Temperature is one of the main parameters in the industrial process control. Yet there are difficulties to have a good control of temperature because of the characteristics of the temperature itself: the temperature inertia is great, its time-lag is serious and it is hard to establish an accurate mathematical model.
There are many methods to be selected in order to control a system. The PID control is simple, easily realized and in most cases it meets the control demand. Fuzzy control has the advantage of quickness, its robustness is good and there is no need to know the object’s mathematical model. This paper analyses the advantages and disadvantages of both PID control and fuzzy control es to the method bining them together, fuzzy self-tuning PID control. In this method, and of the PID controller are adjusted by fuzzy control the paper simulations of PID control, fuzzy control and fuzzy self-tuning PID control are done by MATLAB to control a electric oven. Conclusions are that for those control objects of which models plicated or hard to establish, the PID method has limitation and doesn’t meet the control demand. As the fuzzy control method theory is not perfect, a good control performance cannot be expected. And it could easily cause the stead