Modeling and Control of Electrical Multiphase Machines for Pole-Transition and Fault-Tolerance
Time: Fri 2024-11-22 10.00
Location: Kollegiesalen, Brinellvägen 8, Stockholm
Video link: https://kth-se.zoom.us/s/66083589945
Language: English
Subject area: Electrical Engineering
Doctoral student: Yixuan Wu , Elkraftteknik, EMD
Opponent: Professor, Dr.-Ing. Nejila Parspour, University of Stuttgart
Supervisor: Associate Professor, PhD. Luca Peretti, Elkraftteknik; Professor, PhD. Stefan Östlund, Elkraftteknik
QC 20241018
Abstract
With falling semiconductor prices, multiphase electrical machines are gaining more attention from academic and industrial research. So-called variable-pole machines are multiphase induction machines with squirrel cage rotors with the ability to be excited with a different number of magnetic pole pairs. Using this kind of machines can reduce the total cost of ownership of an electrical drive, mainly through reduction of the cost of running and the cost of NOT running. The omission or reduction of the mechanical gear has the potential to increase the overall system efficiency. Moreover, the additional degrees of freedom allow for true fault tolerance.
This work first introduces the harmonic plane decomposition theory for a unified machine model independent of the excitation of the variable-pole machine. This allows continuous modeling in any condition without model discontinuity. Based on the harmonic plane decomposition, this work presents vector control schemes. Subsequently, it presents pole transition strategies generating the control references for minimum torque dip pole transitions. Moreover, flux weakening during the pole transition maintains the voltage within the drive’s limits.
Next, this work presents the harmonic-plane-decomposition fault detection, a fast, non-invasive, and computational lean fault detection for variable pole machines. By leveraging the additional degrees of freedom due to the increased amount of independent currents, the fault detection shifts partially from information over time to information over space. It continues by demonstrating a pole transition under faulty conditions by adapting a minimum stator copper losses current injection post fault control such that it can carry out a pole transition. In this way, true fault tolerance is achieved.
Lastly, this work also shows a sensorless operation of a multiphase electrical machine capable of operation at low and zero speeds. This is achieved by separating the torque generation and the sensorless observer in different harmonic planes as well as introducing feedback for all estimated state variables.
This work shows technical solutions to take advantage of all independent currents in a variable-pole machines. Applying these techniques in a drive system poses electrical drives with such machines as a viable option for industrial and traction applications.