Abstract:
AC machines are desirable over DC machines. Because of their simple and utmost robust structure without any mechanical commentators. Considering the machine efficiency, reliability, durability, power factor, ripples, stable output voltage and torque, three phase induction motor stays on the top. When we start the motor, rotatory magnetic field starts inducing emf on rotor, but initially rotor acts as a short circuited transformer and it takes time to build up voltage across it, and draws seven to eight times rated current, this continues for some time, which may burn the winding. So we need a starter that limits the starting current and starts the motor soft and smoothly. Throughout previous times, mechanical starters like we delta, direct online and autotransformer starters were used. But they could start single motor and had lack of efficiency. Soft starters is a solid state device that controls the starting current of motor by adjusting the gate pulse of switches like IGBT, thyristor and MOSFET.” In this study, a closed loop soft starting technique by means of controlling supply voltage using IGBT’s, 8 bit pic18f4431 controller and hall effect current sensor acs712 is implemented, which starts multiple motors on the basis of their selection. Supply voltage is provided smoothly in the form ramp function to minimize the inrush starting current. This has done by adjusting the pulse width fed by controller to the gate of IGBT.
