Fault-Tolerant Soft Starter Control of Induction Motors With Reduced Transient Torque Pulsations

Fault-tolerant operation of induction motors fed by soft starters when experiencing thyristor/silicon-controlled rectifier open-circuit or short-circuit switch fault is presented in this paper. The present low-cost fault mitigation solution can be easily retrofitted, without significant cost increase, into the existing off-the-shelf three-phase soft starters to enhance the reliability and fault-tolerant capability of such soft starter systems. In the event of either thyristor open-circuit or short-circuit switch fault in any one of the phases, the fault-tolerant soft starters are capable of operating in a two-phase control mode using a novel resilient closed-loop control scheme. The performance resulted from the present fault-tolerant soft starter control has demonstrated reduced motor starting transient torque pulsations as well as reduced motor inrush current magnitude. The present fault-tolerant approach is applicable to any soft starters that control small to large integral horsepower induction motors. Simulation results along with supporting experimental results for a 1.492-kW, 460-V, four-pole, three-phase induction motor are presented here to demonstrate the soundness and effectiveness of the present fault-tolerant approach.