Abstract
As previously reported [1-3], ArcelorMittal has a specific electrical steel product line for core laminations, which optimises the performance for automotive traction electrical machines. This iCARe® product family consists of Save grades allowing for higher efficiency, Torque grades allowing for higher torque density and Speed grades for high speed rotors. The iCARe® electrical steels now have been developed towards further loss reduction and polarisation increase. This paper shows the improved machine performance achievable by using these new iCARe® grades. Automotive traction machines require high power density, high efficiency and high torque, to maximise the powertrain’s performance and minimise the use of battery power. Permanent magnet synchronous machines (PMSM) are the preferred choice for electric and hybrid vehicles. When searching for cost reduction via eliminating the need for permanent magnets, wound rotor synchronous machines (WRSM) are an alternative. In this paper, a material comparison study is presented for both a PMSM and a WRSM having the same nominal speed and rated mechanical power. The reference case uses M330-35A electrical steel. The impact of switching to either Save or Torque grades of the latest generation is compared numerically: to determine the efficiency of each combination of machine topology and lamination type, the ArcelorMittal loss model is used [4], an extension of Bertotti’s loss model [5]. The impact of each grade is checked by varying the stack height whilst keeping the output power level constant. Hence the bill of materials is affected, reflecting the amount of active materials (laminations, magnets, windings) needed within each machine type, depending on the chosen electrical steel grade. The results show the efficiency benefits when using low loss Save grades and the torque density benefits when using Torque grades. Moreover, the new Torque grades with lower losses present a new potential for further machine performance enhancement: for instance the Torque 27 grade combines outstanding increase of torque density with high efficiency.
Highlights
Electrical machines for propulsion of electric, hybrid and fuel cell vehicles need to present high power density, high efficiency and high torque at minimal cost
The following conclusions can be drawn from this numerical study, when comparing the investigated iCARe® electrical grades with the reference grade M330-35A:
ICARe® Torque grades result in a good compromise between high torque production and low losses of all active materials
Summary
Electrical machines for propulsion of electric, hybrid and fuel cell vehicles need to present high power density, high efficiency and high torque at minimal cost. The “classic” solution has been the use of permanent magnet synchronous machines (PMSM) given its high compactness and good break-away torque. This paper presents a case study of both PMSM and WRSM topologies, aiming for a numerical comparison of traction motor performance versus its bill of materials, for different choices of electrical steel. For a given application this translates on the material level into finding the optimal electrical steel having the best compromise between high polarisation and low iron losses. The iCARe® Save grades typically enable the machine producer to reduce the active material losses and to improve machine efficiency, whereas iCARe® Torque grades assist to produce more air gap flux, allowing the motor to develop more mechanical output for a given motor weight
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