Enhancement in thermal monitoring and fault tolerance in multiphase electric drives

Resum

Multiphase electric drives have emerged as a potential solution for a number of in- dustrial applications due to their benefits compared with their three-phase counterparts; namely, lower current per phase, fault tolerance, and lower torque ripple, to name a few. To exploit the aforementioned advantages, the research and development in the field of multiphase drives has been a very active area in recent years. The main reasons for these developments are related to an increment of the electrification of safety critical ap- plications such as electric and hybrid electric vehicles, ship propulsion, the "more electric" aircraft, locomotive traction, and remote wind farms. Fault tolerance is crucial for all the applications requiring a high degree of reliability, and hence it is one of the most studied topics in multiphase drives. However, although multiphase drives are claimed to be "fault tolerant", true fault-tolerant operation involves the following processes: conditioning monitoring, fault detection, and post-fault control. This dissertation is mainly focused on the first and the last aspects. Regarding three-phase machines, several strategies have been proposed for thermal monitoring based on dc-signal injection. However, due to such injection, a certain torque ripple is produced. In this dissertation, the additional degrees of freedom available in multiphase drives for condition monitoring are exploited to develop an algorithm based on dc-signal injection that enables the drive to estimate online the stator winding tem- perature avoiding the production of torque ripple. Open-circuit phase faults are, by far, the most studied case scenario. For this situ- ation, it is important to develop a suitable post-fault control strategy so that the best performance of the drive in terms of torque ripple, torque operation range (TOR), and minimum losses is achieved. The already proposed post-fault strategies do not minimize the stator winding losses in the whole torque operation range TOR. Thus, in this thesis, a post-fault strategy that improves the performance of the previous ones in this regard is developed. Aside the minimization of the stator winding losses under faulty situation, the con- verter losses also play an important role in the whole drive, and hence, they should be considered in the analysis. Therefore, in this dissertation, a comparison of the main post- fault control strategies in terms of converter losses for dual three-phase machines is carried out. In addition, a strategy aiming to optimize both the converter and the stator copper losses is obtained and also compared with the previous ones. Contributions of this dissertation have been published in three JCR-indexed journal papers and presented at two international conferences.