Quality control of low-cost electric machines for electric vehicles by DOE assisted six sigma DMADV method

Electric machines are the essential parts of the electric vehicle (EV) propulsion system. High performance and low-cost electric machines are desirable in mass production of EVs. Well-known for its economical control and global dominance of machine manufacture, China must now focus on quality control of the new generation of EV motors to prepare for the uptake of the EV market. This paper proposes a quality control approach to minimize variability of EV electric machine performance. The methodology of Six-Sigma DMADV is introduced into the quality control approach, the key of which is to control the geometrical tolerances of the machine parameters as the performance of a machine is fundamentally determined by its physical geometry. Due to a large number of tolerances need to be considered simultaneously as they are coupled with each other, “trial and error” or “one factor at a time (OFAT)” are not applicable in the quality control study. It is proposed to use design of experiment (DOE) method, which provides credible prediction and substantially reduces trial samples and computation time. The DOE assisted Six Sigma DMADV method is thoroughly discussed in the paper and validated at the end by a prototype of low-cost internal permanent magnet (IPM) machine with ferrite permanent magnets.