Fuzzy logic based soft starting of induction motor with current control

Abstract

Induction Motors are the most commonly used machines in industries mainly because it is robust, inexpensive and easy to maintain. For an Induction Motor, the starting current is around ten times the rated current and this persists for a few cycles. This may be very much detrimental for the machine and hence there is a need for using starters to limit the starting current. During earlier times, mechanical starters like star delta, direct online and autotransformer starters were used. Thyristorized soft starters are of low cost. Their reliability is on the higher side and they are simple and occupy lesser space, and hence their use is a fruitful solution to the induction motor starting problem. The ac motor starters incorporating power semiconductors are used frequently nowadays for their controlled soft starting ability with reduced starting current. In this study, a closed loop Matlab Simulink model is developed which would reduce the current at the soft starting period. A fuzzy logic based soft start scheme for induction motor drives is used which would give optimal performance. Fuzzy logic has received higher emphasis in the field of power electronics because of its adaptive capability. The three phase stator currents are converted into two phase currents. The magnitude of current is then converted to per unit. Then it is compared with a reference value. The error is passed through a Fuzzy Logic Controller (FLC).The FLC output is used to control the amplitude of the reference sine wave. Hence by controlling the modulation index, the applied voltage to the stator is controlled and hence the starting current is limite