PLC BASED FUZZY LOGIC CONTROLLER FOR SPEED

Abstract

Basically, Programmable Logic Controller (PLC) consists of input/output, memory, CPU and power supply. PLC executes program like a microprocessor device and changes output condition after reading input status. PLC is widely used in industries for sequential control and continuous control. In past, PLC was used for sequential control as a replacement of relay logic. Nowadays PLC provides variety of functions like, digital input/output, timers, counters, PWM output, analog input/output and P, PI, PID, 2/3 point regulation for continuous control. Successful implementation of the fuzzy method for speed control of DC motor using a general-purpose programmable logic controller (PLC) is demonstrated in this work. Speed control of DC motors by a changing armature voltage is a common practice throughout industry at the present time. In addition, general-purpose PLCs are the most common controllers utilized for the control of industries and power plants. However, this work suggests a method for increasing the utilization level of an existing general-purpose PLC. In effect, the PLC is requested to perform the additional task of speed control using the elegant and effective fuzzy scheme. With a control scheme based on fuzzy methods, the speed control algorithm has been implemented within the standard PLC ladder logic. Application of fuzzy logic controller in control systems proved to be superior to the conventional controllers like P, PI, PID controllers. PID type controllers do work fine when the process under control is in a stable and linear condition. Also they do not cope with the dead time of process. Fuzzy logic controllers can infer coherent results in dead time, nonlinear and unstable conditions. It is very desirable to integrate conventional control engineering techniques, such as ladder logic or instruction list language for digital logic and PID control blocks tightly together with fuzzy logic functionality. In present work, fuzzy logic algorithm (fuzzy PI and fuzzy PID) is implemented on GE/7 PLC for continuous speed control using ladder logic