Design and Analysis of a Thyristor Based Three Point Automated Starter for DC Motor

This article presents a novel automatic starter circuit design for a separately excited DC motor, including a sequential resistor shorting mechanism using thyristors. In the proposed design, four identical resistors are connected in series with the motor armature during the initial starting phase to limit the high inrush current. As the motor speed increases and sufficient backEMF is developed, each resistor is sequentially bypassed. The starter design automatically shorts the resistors stepwise as the armature current decreases with the motor's increasing speed. This approach offers improved control over the motor starting process and eliminates issues associated with traditional mechanical starters (3-point/4-point). The thyristor triggering circuit is developed using low-voltage MOSFETs to ensure proper sequencing of the thyristor triggering. Finally, the design is connected to a 3.7 kW separately excited DC motor to experimentally validate the proposed starter designed starter design.