Design of Low-Cost PLC to Drive Three-Phase Induction Motor using Variable Frequency Drive

In this paper, we have designed a low-cost indigenous logical control that is not only affordable by micro-and small-scale industries to further the manufacturing and production processes but also to add value to the accuracy and reliability of process automation. A Programmable Logic Controller (PLC) is a specialized computer used for the control and operation of manufacturing processes and machinery. The logical control is designed with two microcontrollers, which are programmed to interface with the Human Machine Interface (HMI) panel and also to communicate with the variable frequency drive. Here, the analog signal scaling method is used to vary the frequency for induction motor speed control. The range of speed achieved was both step-wise and in a continuous manner. The developed prototype is verified in the laboratory as well as with loading conditions, i.e., lathe and computer numerical control (CNC) machines at 40 degrees C.