Mapping of IPM machine efficiency and Noise Vibration Harshness : An investigation into trade-offs with respect to efficiency and Noise Vibration Harshness

Abstract: Due to the recent shift towards electrification, electric machines has become a prominent option to be used in vehicle applications. Much effort is spent in the development process of these machines to make optimizations in order to improve the performance aspects of the machine. A key aspect to consider during electric machine development is the harmonics produced by the electric machine’s inverter and the topology of the machine. These harmonics will have consequences for the various performance aspects and are thus important in the analysis of the machine. This thesis investigates how the harmonic content in the machine affect two of these performance aspects; the efficiency and the vibrational levels. In order to conclude how the harmonics affect these aspects, quite complex translations from harmonic level to performance level are required. This thesis has performed such translations on a specific motor topology called Internal Permanent Magnet Synchronous Machine (IPMSM). The calculations have been done for a multitude of operating points in order to render two sets of high-fidelity maps, showcasing the efficiency and the mean radial tooth force for the entire operating region of the electric machine. In order to understand how the efficiency and vibration changes with harmonic content, the maps have been constructed for 3 different switching frequencies; 6, 8 and 10 kHz. The purpose of these maps is to increase the design space for motor control engineers by providing a tool that helps to make more informed decisions on how switching frequency impacts the various performance aspects in the machine. In order to facilitate this work, simulations based on the geometry of the IPMSM were performed. The current waveform for this simulation has been generated by an external circuit consisting of a control loop and an inverter in order to generate the harmonic components. Based on the results of these maps, one can conclude that the machine specific losses decrease for higher switching frequencies. However, the efficiency gains in the machine decreases further up in the switching frequency domain. The inverter instead continues to lose efficiency quite linearly across as the switching frequency domain. The mean radial tooth force showed a tendency to decrease for higher switching frequency. However, certain operating points still showed a higher tooth force for higher switching frequencies.