A Practical Approach to Hairpin Winding Design: Patterns Investigation, Feasibility Verification and Fractional Slot Solutions

Abstract

The hairpin winding technology is increasing its impact in the industrial and automotive sectors, thanks to the well-known advantages in terms of motor performance and manufacturing process. Since wave patterns must be adopted, there are significant differences compared to the traditional winding design, in particular concerning the parallel paths conductors disposition. Design rules for hairpin windings with parallel branches are proposed in literature to avoid circulating currents and extra losses. Due to the nonlinearity or in case of short pitched windings, some patterns present a weak symmetry and parasitic currents can circulate. This paper investigates the circulating currents issue in commonly adopted hairpin winding patterns, analysing working points with different saturation levels and speeds. New patterns for more than 2 parallel branches are proposed with reduced parasitic currents with respect to the already known solutions. In the second part of the paper, fractional slot winding configurations are proposed.