PLC在闭环控制系统中计算偏差信号的方法

The Calculation Method of Deviation Signal for Closed-loop Control System Based on PLC

闭环控制系统中,控制器将给定信号与反馈信号进行比较后得到偏差信号,再将偏差按照一定的控制规律进行运算,实现对过程参数的自动控制。针对模拟式控制器,需要硬件电路转换属于不同量纲的给定与反馈才能计算偏差的特点,提出一种不需要转换电路,通过PLC的软件设计,直接计算偏差信号的方案。重点考虑PLC对模拟量信号的滑动平均值滤波与缩放处理。实践证明,该方案不仅节省硬件资源,而且增强了抗干扰能力,可广泛应用于工业闭环控制系统中。

In the closed-loop control system, reference signal and feedback signal are compared by the controller to generate deviation signal, and then the deviation is calculated according to the control law to re- alize the automatic control of the process parameters. When the reference signal and feedback signal belong to different dimensions, the analog controller needs the hardwired connection as a converter to calculate the deviation. This paper proposes a method directly calculating the deviation signals by designing PLC software rather than relying on a converter. The moving average filtering and scaling of analog signals are particularly elaborated upon. Practice shows that the method can save hardware resources, improve the capacity of resis- ting disturbance, and thus be widely applicable in industrial control system.