Abstract
Thermal analysis represents a key factor in electrical machine design due to the impact of temperature increase on insulation lifetime. In this context, there has been a wide investigation on thermal modeling, particularly for machines used in harsh working conditions. In this perspective, brake-by-wire (BBW) systems represent one of the most challenging applications for electrical machines used for automotive smart actuators. Indeed, electro-actuated braking systems are required to repeatedly operate the electric machine in high overload conditions in order to limit the actuator response time, as well as to enhance gravimetric and volumetric specific performance indexes. Moreover, BBW systems often impose unconventional supply conditions to the electric machine, consisting of dc currents in three-phase windings to keep the rotor fixed during the braking intervals. However, a dc supply leads to uneven temperature distributions in the machine, and simplified thermal models may not accurately represent the temperature variations for the different machine parts. Considering such unconventional supply conditions, this paper initially investigates the applicability of a conventional lumped-parameters thermal network (LPTN) based on symmetry assumptions for the heat paths and suitable for surface-mounted PM synchronous machines used in BBW systems. An extensive test campaign consisting of pulses and load cycle tests representative of the real machine operations was conducted on a prototype equipped with several temperature sensors. The comparison between measurements and predicted average temperatures, together with insights on the unbalanced heat distribution under the dc supply obtained by means of finite element analyses (FEA), paved the way for the proposal of a phase-split LPTN with optimized parameters. The paper also includes a critical analysis of the optimized parameters, proposing a simplified, phase-split lumped-parameters thermal model suitable to predict the temperature variations in the different machine parts for PM synchronous electric machines used in BBW systems.
Highlights
Permanent magnet synchronous machines (PMSMs) are nowadays widely used in the automotive industry for the electrification of smart actuators
lumped-parameters thermal network (LPTN) were proposed paths in the machine with finite element analyses (FEAs), ‘asymmetrical’ LPTNs were pro- to closely matchmatch the temperature evolution for eachfor stator phase and all the machine posed to closely the temperature evolution eachwinding stator winding phase and all parts, both for the test conditions and the operative load cycles
The literature reports a considerable number of research papers that focus on thermal analysis of electric machines
Summary
Permanent magnet synchronous machines (PMSMs) are nowadays widely used in the automotive industry for the electrification of smart actuators. Electric braking is a cutting-edge technology in which the traditional hydraulic brake architecture is substituted by electro-actuated braking sys- the traditional hydraulic brake architecture is substituted by electro-actuated braking systems tems supplied at 12 or 48 V. In addition to dimension and weight constraints, the machines used in these actuators are operated in overload conditions to limit electric the machines used in these actuators are operated in overload conditions to limit the brake brake response time and, the vehicle braking distance. Conventional lumped-parameters thermal models based on circumferenential symmetry assumptions for the heat paths may not properly predict the temperature tial symmetry assumptions for the heat paths may not properly predict the temperature variation for the different machine parts during the real operation.
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