PLC BASED CONTROL OF 3-PHASE INDUCTION MOTOR DRIVEN BY 1-PHASE SUPPLY

Abstract

Smith connection is a new winding connection that enables a three-phase induction motor to achieve perfect phase balance when operating on a single-phase supply. Three-phase induction motors are nowadays available with 6 or 12 terminals brought out for the three-phases. With this new unique connection of the terminals and with three capacitors it is possible for the induction motor to operate with balanced phase currents and phase voltages at a particular load if the motor impedance angle is between 300 to 60° . This three-phase motor on single-phase supply has lower cost and high efficiency than a comparable-quality single-phase motor. Phase imbalance would result when the rotor speed or load has been changed. To ensure satisfactory machine performance over a wide load range, the concept of multi-mode operation was used. In this report multi-mode operation of an induction motor with the Smith connection, with the automatic control being realized by Programmable Logic Controller (PLC) has been implemented. A systematic analysis of the Smith connection that enables perfect phase balance to be achieved in a three-phase induction motor when operating on a single-phase supple has been discussed . PLC may be viewed as a. compact computer having digital,. analog I/O modules with memory system- so that we can read or write programs. Its analog module contains built in A/D and D/A functions which reduces the circuit complexity and improves the system reliability. Using PLC we can implement logic, sequencing, timing, counting and arithmetic control through digital or analog input or output modules. iii Experimental work has been done on a 3.7-kW induction machine, by taking stator voltage as the control signal. Ladder diagram has been developed to implement the necessary control action using KV-300 PLC. Solid State Relays are used to switch ON/OFF the capacitors. Experimental results are compared with the theoretical values to confirm the feasibility of the proposed controller. iv