Fault Tolerant Operations in Adjustable-Speed Drives and Soft Starters for Induction Motors

Fault tolerant operations of soft starters and adjustable-speed drives (ASDs) when experiencing power switch open-circuit or short-circuit faults are presented in this paper. The present low-cost fault mitigation solutions can be retrofitted into the existing off-the-shelf soft starters and ASDs with only minimum hardware modifications. The fault tolerant soft starters are capable of operating in a two-phase mode under the condition of thyristor/SCR open-circuit or short-circuit switch-fault in any one of the phases using a novel resilient closed-loop control scheme. The performance resulted from the present soft starter fault tolerant control has demonstrated reduced starting motor torque transient and inrush current magnitude. As for the ASDs, a low-cost fault mitigation strategy for low-speed applications such as "self-healing/limp-home" needs for vehicles and propulsion systems, with capabilities for mitigating transistor open-circuit and short-circuit switch-faults was developed. The present fault tolerant drive topology requires only minimum hardware modifications to the conventional off-the-shelf six-switch three-phase drive, with only the addition of electronic components such as triacs and fast-acting fuses. In addition, the present approach offers the potential of mitigating not only transistor switch-faults but also drive related faults such as rectifier diode short-circuit fault or dc link capacitor fault. Given in this paper is a complete set of simulation results that demonstrate the soundness and effectiveness of the present fault tolerant approaches.