PLC based power factor correction of 3-phase Induction Motor

A Programmable Logic Controller (PLC) based power factor correction method for a 3-phase Induction Motor (IM) through switching of shunt capacitors is proposed in this paper. A 3 phase IM has a low power factor (pf) at no load as it draws large magnetizing current and the active power delivered to the motor is low, which is utilized to overcome the no-load losses. The PLC based power factor improvement algorithm is developed and implemented on a 3 Phase laboratory prototype IM coupled to a DC generator and the effectiveness of the algorithm is tested under no-load and loaded condition. Based on the instantaneously measured value of power factor, the PLC switches the appropriate bank of capacitors into the circuit depending on the load condition to improve the pf. Large scale use of PLC in industrial automation, adaptability, simple implementation and economics justified its selection as the switching controller. A significant improvement in power factor under different loading conditions is observed.