Transient Torque Peak Reduction During DOL Starting of Three-Phase Induction Motors Using Zero-Crossing Switching Approach

Induction motors have widely been used in industrial factories due to their simplicity of design and operation, low cost of maintenance. The most common approach for starting them is a direct-on-line (DOL) method. However, it produces a large transient torque, causing a shortened lifetime of mechanical rotating parts of the motor, driven load, and gearbox. Therefore, this paper presents a generalized zero-crossing switching approach to reduce an unnecessary peak torque amplitude during the DOL start. Unlike the conventional DOL technique, the proposed method requires zero-crossing detection. When a random closing command is initiated, one of the three-phase voltages that go to zero first is regarded as a referenced voltage for connecting a pair of the remaining two voltages simultaneously at the exact instant when it crosses the zero point. The motor is initially started under two-phase operating mode. After a given 1/2 cycle of delay time is expired, the referenced voltage is subsequently supplied for a continued operation in full three-phase mode. The experimental and simulation results confirm that the proposed technique can help to alleviate the starting transient torque peak arising from the serious drawback of the DOL starting.