Feasibility Analysis of Multiphase Machines for Electric Vehicle Applications

The feasibility of utilizing multiphase machines in electrical vehicles (EVs) is investigated in this paper by designing three-phase, five-phase, six-phase, and nine-phase interior permanent magnet synchronous machines (IPMSMs) with the same sizing parameters as the Tesla Model 3 IPMSM which is used as a reference. The optimized three-phase machine results in a 20% higher average output torque per permanent magnet (PM) volume compared to the reference design. Multiphase machines show 3-5% higher torque per PM volume over their three-phase counterpart while achieving inherently low torque ripples. The torque-speed analysis of the multiphase machines demonstrates enhanced efficiency regions attributable to the increased output power although this improvement is accompanied by increased iron losses due to high winding factors of harmonics. PWM losses are calculated, and thermal simulations of the machines are performed to validate that the designs work with thermal limitations. It is also shown that the DC-link capacitor size can be reduced by up to 55% compared to a three-phase system by using a multiphase structure. The total number of power switches used in the drive remains the same for the six-phase machine since the lower phase currents can be achieved by increasing the number of phases. The cost analysis for each of the machines has shown that multiphase machines are not necessarily more expensive than three-phase machines since the same total number of switches considering paralleled switches in three-phase machine can be used in six-phase machine while having smaller DC-link capacitors and PM volume. As a result, 14.2% higher output power per cost can be achieved compared to the reference design.