Efficiency and utilization benefits of five-phase squirrel cage induction and permanent magnet synchronous machines with third harmonic voltage injection

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Subject of innovation: The objective of this research project is the systematic comparison of pulse width modulation inverter-fed three- and five-phase squirrel cage induction (SCIM) and permanent magnet machines (PMSM) concerning maximum efficiency, torque per total loss ratio and torque per volume at a given temperature rise of the stator winding. Content of the project: The investigation is based on a standard three-phase induction motor (15 kW, 1474 /min, 400 V) and a standard three-phase inverter from well-known manufacturers. For the same mechanical, electrical, thermal and geometrical constraints, a five-phase SCIM and a three- and five-phase PMSM are analytically and numerically designed. The four machines are built and an experimental study shall verify the theoretical results. Preliminary work: Analytical and numerical calculations led to the design of several five-phase SCIMs for an automotive supplier. The benefits and drawbacks of five-phase SCIMs versus PMSMs for the special application of a belt-starter-generator were worked on. Basic findings were published or are in preparation for publication. Objective of the project: As a thorough comparison of three- versus five-phase SCIMs and PMSMs concerning achievable efficiency and motor utilization is still missing, a theoretical and experimental comparison at identical active mass will highlight the possible benefit of an increase of phases from three to five and of the third harmonic injection. The following questions shall be answered by the proposed research project: a) At rated operation: How does the torque per total loss ratio change by the increase of phases from three to five? Do five-phase machines operate more efficient than three-phase machines? How much does the efficiency improve if third harmonic injection is applied? b) Can the maximum achievable torque (overload capability) at the inverter current limit be increased by an increase of phases from three to five? c) How is the rotor topology influenced by the increase of phases from three to five? The number of rotor bars and the skewing angle shall be analyzed for the SCIM. The magnet arrangement (buried, surface, V-shape) shall be analyzed for the PMSM. d) How is the performance in terms of maximum torque and efficiency influenced in field weakening range by an increase of phases from three to five? e) How is the acoustic noise, the vibration and the torque ripple influenced by the increase of phases from three to five? A final recommendation for the use of three- or five-phase machines and general rules for design and application of third harmonic voltage injection shall be the final output of the project. General rules on the benefits of five-phase SCIMs and PMSMs will be set up. These results shall help to judge if the increased system complexity is worth the benefits of five-phase variable speed drives.