PLC based DC drive control using Modbus RTU communication for selected applications of sugar mill

DC Drives are serving in industries with their efficient motion control ability. These Drives can operate in Local Mode as well as in Overriding Control mode. In Local Mode the Drive is controlled by its control panel where as in Overriding Control mode, it can be controlled remotely by a Programmable Logic Controller (PLC). This PLC based control of Drive is essential for process control in industries like Sugar Mill. Further, this control can be employed using any of the industrial communication protocols which reduce the wiring complexity. Modbus Remote Terminal Unit (RTU) is one such protocol which is open, robust and widely used in industries because of its simplicity. Therefore the same protocol has been implemented in the presented work. This paper depicts initially about configuring a DC Drive (DCS800 of ABB) for Modbus RTU communication and a preliminary test to verify the proper working of intermediate components and cables by communicating the Drive with PC using Modscan32 software. Later, the PLC and Drive communication details and development of ladder program are presented. Further, the results obtained from testing PLC-Drive communication considering the two applications of Sugar Mill are put forth. These ensure the successful implementation of PLC-Drive communication. The applications considered are; speed raise and lower of a DC motor by PLC and secondly, achieving a speed pattern (speed versus time graph) required by a process of Centrifugal Machine in Sugar Mill.