Analysis of Copper Loss and Discharge Characteristics of Litz Wires and Flat Wires in Brushless Air-Core Pulsed Alternators

Pulsed alternators can generate extremely large instantaneous currents and are suitable for pulsed power loads such as rail guns. The traditional armature winding self-excitation synchronous pulsed alternator contains high-power carbon brushes and slip rings in its structure, which limits its development toward higher rotational speed and higher power. In recent years, many scholars have proposed a variety of new topologies for brushless air-core pulsed alternators, eliminating the carbon brush and slip ring structure. However, the magnetic field and current frequency on the stator side are relatively high, resulting in huge copper loss under pulsed discharge conditions. This article optimizes stator windings of a brushless air-core pulsed alternator and analyzes the influence of different Litz wires and flat wires on the slot fill factor, dc resistance, and ac resistance. The theoretical calculation model and finite-element simulation model of different wire types are established. The effects of wire types and transposition method on dc copper loss, eddy current loss, circulating current loss, and discharge current peak under extreme discharge conditions were obtained. On this basis, combined with common pulsed discharge conditions, a comprehensive comparison of copper loss and discharge characteristics during the discharge process of different wire types was carried out. The results show that selecting the appropriate wire type according to different loads and stator electrical frequency can help improve efficiency and discharge performance.