Abstract
Research and/or Engineering Questions/Objective
Introducing 48V mild hybrid system into conventional vehicles can effectively reduce fuel consumption and CO2 emission. The belt starter & generator (BSG) machine, as the core component of the 48V system, is required to be designed with high efficiency, high power/weight ratio and low cost. An 8- pole/36-slot machine with common winding and an 8-pole/48-slot machine with hair-pin winding has the same design of rotor structure are designed and compared to find an optimal design. The calculation and analysis of Electromagnetic field is done by finite element method.
Methodology
Two IPM machines are designed for the application in a 48V mild HEV system, and the specification of the machine is listed. Due to the limitation of winding design and manufacturability, two stators sharing the same 8-pole rotor structure were developed to accomplish the same design requirements, one with a 48-slot hair-pin winding and the other with a 36-slot common winding. The no-load performance, the inductance parameters, and the load performance including the external characteristics, the torque-perampere characteristics, the current distribution, efficiency, and torque ripple were analyzed through electromagnetic FEM calculation and compared. Besides, the volume, weight and manufacturability of machines were also considered. Finally a bench test was performed to exam the analysis result.
Results
This paper compared two machine design of a 48V mild HEV system. The 8-pole/48-slot machine with hairpin winding has a better performance on torque density which value is 18% bigger than the common winding, and it saves about 20% volume. The 8-pole/48-slot machine with hairpin winding has an advantage on torque-per-ampere, so the requirement of inverter current is about 10% lower than the other. On the other hand, because of the winding type and pole/slot combination, the 8-pole/36-slot machine with common winding has a better performance on the harmonic, cogging torque and torque ripple. Considering the limitation of space and cost, the 8-pole/48-slot machine with hairpin winding is chosen for a 48V mild HEV system.
Limitations of this study
The present stator design has different slot number due to the limitation of stator dimension and manufacturability. And the skin effect and proximity effect in the hair-pin winding are neglected in this study. Usually, the efficiency of high-speed operation points is influenced by these effects. What does the paper offer that is new in the field including in comparison to other work by the authors? The analysis and comparison with two different design of machine in this paper is new as well the application of machine have some certain requirements. A comprehensive comparison has been performed between hair-pin winding and common winding in this paper. It is indicated that the hair-pin winding has more advantage in limited space and cost.
Conclusions
Two different machines for 48V mild HEV system are designed. Advantages and disadvantages of two machines are analysis and compared. Considering the limitation of space, demand for large torque, power density and low cost, the 8-pole/48-slot hair-pin winding design is more suitable for the 48V mild HEV system.
Key Words: 48V mild hybrid system; IPM; Hair-pin winding; Electromagnetic FEM analysis