Superposition techniques for analyzing cogging torque sensitivity to manufacturing errors in fractional pitch PMSM

Abstract

Theoretically, the layout of fractional pitch permanent magnet motors should ensure the cancellation of most cogging torque harmonics. In reality, manufacturing errors lead to incomplete cancellation and higher than expected cogging torque. Two potential manufacturing errors are the variation in angle between successive magnets and the strength of the magnets.To determine the sensitivity of cogging torque to magnet strength and placement, a superposition technique is used. This technique is validated by first demonstrating that the total cogging torque can be reconstructed by summing offset versions of the torque from experimentally determined single-magnet/singleslot interactions.Following this validation, Monte Carlo simulations are conducted to statistically determine the sensitivity of cogging torque to magnet placement and strength errors. It is demonstrated that the mean RMS cogging torque increases by 4 % for every degree increase in magnet placement standard deviation and by 0.06% for every 1% increase in magnet strength standard deviation.

Cogging torque sensitivity considering imperfect magnet positioning for permanent magnet machines of different slot and pole count

“…8 gives the relative increase as function of the positioning error ∆γ for all topologies and all α r /β rcombinations. Overall, the characteristics can be reasonably approximated as linear relationship for any particular setting, which is in agreement with a single design analysis presented in [39]. As can be observed, the 12S8P-topology shows no noticeable cogging increase, while the 12S10P-and the 9S8Pvariant feature up to a 6-and 8-fold increase, respectively.…”

Process capability control procedure for electrical machines by using a six‐sigma process for achieving six‐sigma quality level

“…Kim et al presented a stochastic simulation for analysing variations in motor characteristics due to the tolerance of design variables [9, 10]. A few groups have presented studies on how cogging torque is influenced by the manufacturing tolerance, and how robust design methods can be used to address this problem [11–18]. Cho et al [19] presented reliability‐based optimum tolerance design using the Akaike information criterion (AIC) method to guarantee the high reliability of electromagnetic devices while maximising manufacturing tolerances.…”