Rectangular and Random Conductors: AC Losses Evaluations and Manufacturing Considerations

Abstract

This paper presents a comparison between hairpin and random distributed winding in electrical machines for automotive applications. Indeed, the overall performance of an electrical drive system is seriously affected by its winding design. The considered electrical machine has a peak power of 115kW and a maximum operating speed of 12000 rpm. Both cost and manufacturing aspects are here discussed in detail. Two different machine topologies have been investigated and Finite Element Analysis (FEA) results are presented and discussed. Then, the comparison between hairpin and random winding configuration in terms of AC copper losses are presented for the selected geometry. The accurate AC losses estimation can be done by modelling each single conductor. In order to significantly reduce the simulation time, a domain model reduction has been adopted. Based on two different driving cycles, Urban Dynamometer Driving Schedule (UDDS) and Highway Fuel Economy Test (HWFET), the AC losses have been evaluated. The main outcome of this work is the considerable reduction of AC losses by using a segmented hairpin winding.

Segmented Hairpin Topology for Reduced Losses at High-Frequency Operations

“…The number of parallel-connected elements should be kept low to avoid unfeasible solutions or excessive complications of the bending and welding processes [18]. Although the concept of parallel conductors has been widely implemented in large power machines equipped with pre-formed winding [19], to the of the authors' knowledge the parallel-connected concept in hairpin windings has been proposed in [20] for the first time, but the analysis only focused on the 2D aspects (i.e. end-windings effects are neglected) and no experimental validation was provided.…”

“…This work considers an electrical machine designed for automotive traction with power and maximum speed equal to 115 kW and 12000 rpm, respectively. As detailed in [20], the design and optimization process of such traction motor has led to select a permanent magnet assisted synchronous reluctance machine with 4 poles and 3 rotor barriers per pole, as shown in Fig 1 , and the geometrical parameters are provided in Table I. Regarding the stator, two different numbers of slots-perpole-per-phase q are envisioned (i.e.…”

“…q=2 and q=4), while fixing stator inner and outer diameters. Also in [20], both random and hairpin windings have been considered for the designed motor. In this work, the focus is on the hairpin option and the following layouts are considered: 1) q=2 and number of layers per slot k=4; 2) q=4 and k=8; 3) q=4 and k=44) q=4 and k=6.…”

“…Time harmonic simulations are used for the sake of resolution speed and consistency with the sinusoidal supply assumption. According to the [25] only the stator model is needed to reduce the computational effort without losing accuracy in estimating the AC losses, being the latter mainly dependant on the slot flux leakage [20].…”

Hairpin Windings: Sensitivity Analysis and Guidelines to Reduce AC Losses

“…A 2D analytical model able to calculate AC losses is presented in [17]. In [18], a comparison between random and hairpin windings is carried out always in terms of AC losses. In [19], innovative winding patterns that can significantly reduce AC losses are introduced.…”