Abstract:

The main contribution of this dissertation is the conception and development of a new control strategy that allows Delta-connected induction motors to operate under a faulty two-phase open-Delta mode of operation with a resulting performance characterized by nearly balanced line currents and acceptable levels of torque pulsations in either the open-loop mode of operation, or the vector-controlled closed-loop mode of operation. The main aim and accomplishment of this control strategy is to maintain a quality of performance of a two-phase open-Delta mode of operation of a faulty motor as close as possible to the quality of performance of such a motor under normal healthy three-phase Delta-connection. Hence, one anticipates that such a procedure would be triggered after the process of isolating the faulty phase is accomplished successfully. Typical applications that can rely on the benefits of this newly introduced control strategy are in cases that involve open-coil faults that may occur due to internal winding rupture, loose internal connections, or in cases that involve an inter-turn short-circuit fault that has been diagnosed and successfully isolated in an incipient stage. This control topology does not require any hardware modification or even oversizing of the drive. However, oversizing of the motor may be necessarily if it is required to develop the motor's rated power under this faulty two-phase open-Delta mode of operation. Another advantage of this newly conceived control strategy is that it can be enabled in the three-phase normal mode of operation as well as the two-phase open-Delta mode of operation with hardly any transient disturbance affecting the quality of the torque or the balanced line currents. Thus, this newly conceived control strategy enhances the "robustness" of the system. This is because this control strategy avoids transients that may occur during the transfer between a control algorithm that is provided to control the machine under a healthy operating condition, and another control algorithm that is provided to control the machine under a faulty operating condition "fault mitigation algorithm". The newly conceived control strategy was thoroughly explained and successfully verified through numerous results obtained from several simulation runs and corresponding experimental tests in this dissertation.