PLC混凝投药复合控制系统的设计

Design of PLC-based Compound Control System for Coagulant Dosing Process

针对水厂混凝投药过程的非线性、时滞性等特点,设计了混凝投药控制系统。该系统采用流量比例前馈控制与模糊自整定PID串级控制的复合控制策略,以西门子S7-200 PLC作为处理器核心。介绍了系统的工作原理、控制算法设计、硬软件实现方案。Matlab仿真结果表明,模糊自整定PID串级控制系统的超调量、调节时间和抗干扰能力明显优于常规PID串级控制;此外,由于系统增加了流量前馈控制,使加药量能随原水流量变化及时得到调整。

In accordance with the characteristics of the coagulant dosing process in water works, e.g. non-linearity and time delay, the control system has been designed. Compound control strategy is applied in the system, which adopts flow rate feed forward control and fuzzy self-tuning PID cascade control. Siemens $7-200 PLC is the kernel of the processor. The operational principle of the system, design of control algorithms, implementation of hardware and software are introduced. The system is simulated with Matlab. The overshoot, regulating time and anti-interfer- ence capability of fuzzy self-tuning PID cascade control system are all better than those of conventional PID cascade control, and since flow feed forward control is added, the dosage can be adjusted on time following variation of raw water flow.