Comprehensive Load Loss Model of an Ironless Machine: Advantages of Current Source Inverter Supply

Abstract

Accurate lossmodeling in electric machines is a critical enabler for design optimization. By providing more faithful estimates of thermal stress, loss models may also contribute to extended insulation and permanent-magnet lifetimes. Loss modeling has been widely investigated, and existing approaches can be broadly grouped into three classes: (i) analytical models; (ii) numerical finite-element (FEA) methods; and (iii) hybrid schemes that combine analytical formulations with numerical field solutions. Ironless (coreless) machines constitute a special case for AC loss prediction. In such topologies, iron-core losses are essentially absent, so winding AC losses tend to dominate, and magnet losses may become non-negligible under high-frequency excitation. AC losses of these machines, which are suitable for FESS applications, have been under-investigated in literature. This paper presents a comprehensive loss model for ironless machines that jointly treats winding and magnet losses and distinguishes between fundamental and carrier-frequency components for both coils and magnets. The framework is experimentally assessed on a prototype for a flywheel energy storage system (FESS) application. A current source inverter (CSI) supply appears to reduce AC losses and current ripple relative to a conventional voltage source inverter (VSI), suggesting potential efficiency and thermal advantages for ironless drives under comparable conditions.