Abstract
AC Voltage Controllers are finding important application in speed control of induction motors, light dimmers, heat controllers and soft starters. AC Chopper is an arrangement of bi-directional switches to control the output voltage by varying the duty-cycle of operation of the switches involved. In this paper, a new switching scheme for three phase ac chopper is discussed which requires only three variables for converting the fixed input ac voltage to a controlled ac voltage. The added advantage is that this scheme takes into account the safe operation of the ac chopper by preventing short-circuit conditions. At the same time it provides a path to the motor current when the terminal voltage falls to zero. Implementation of the proposed scheme leads to much simpler control circuitry than discussed in the literature. A Three phase 3HP induction motor-fed from three phase ac chopper is used for the work. The simulation results confirm the improvement in power factor, leading to power savings.
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