Implementation of a laboratory-based low cost AC Chopper Soft-Starter

This paper presents a laboratory scale implementation of an AC Chopper Soft-Starter topology for Three Phase Induction Motors, which was designed to be used in power quality and in power electronics didactical laboratories, as a project proposal for students from electrical engineering and from control engineering. The issue of costs was considered as a constraint, most of the components were chosen based on feasibility of the project and the availability of the local stores. To reduce the required programming skills, the control algorithm was developed using Arduino platform. The paper also presents the simulation results and the real results of the prototype.

Introduction

The three phase induction motor is the most significant load in the industrial plants, with a demand that may exceed more than half of the delivered electrical energy [1]. Different from the other common loads, these motors present a highly inductive characteristic. The induction motor circuit behavior may be compared to a power transformer with shorted circuited secondary terminal. Fig. 1 shows the equivalent circuit of an induction motor, where it can be seen that when the motor is static, the slip (S) is maximum , resulting in R_L equals to zero. In consequence of this fact, there is a large current through the terminals of the motor at the starting procedure. Fig. 1.

Equivalent circuit of an induction motor.