Lumped-Parameters Thermal Network of PM Synchronous Machines for Automotive Brake-by-Wire Systems

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.

Thermal Evaluation of a Short-Operating-Duty Dual-Lane Fault-Tolerant Actuator for Aerospace Applications

“…Note that when a more complex thermal model or limited test points experimental data is available an alternative approach of deriving thermal parameters is frequently used [24]- [26]. A search (optimisation) algorithm is employed to estimate the thermal parameters, which are challenging or not possible to derive directly from the measured data.…”

“…It is important to note that formulating the design procedure is non-trivial and requires a good balance between the models' fidelity and computational effort required to derive a feasible machine design. This problem is further exacerbated when analysing fault-tolerant machines, where alternative operating scenarios need to be considered [4]- [13], [24]- [25]. Frequently, design candidates from such a design process require further assessment to provide a more detailed and definitive insight into the machine performance.…”

Thermal Management in Electrical Machines

“…Graffeo Federica et al [3] present an improved, yet simplified thermal model, of an electrical machine used in a brake-by-wire (BBW) application. A conventional LPTN, based on symmetry assumptions, was investigated.…”

Multiple Physics Design of Induction Motor

“…On the other hand, the resistor element refers to the heat transfer over the system. Its function is conduction, heat dissipation, and radiation events, and it helps to analyze steady-state temperatures [8].…”

“…It usually takes place in liquid and gaseous environments. In Newton's law of cooling, it is expressed as:(8) where Q is the heat transferred per unit time; A is the area of the object (m 2 ); h, heat transfer coefficient (W/m 2 K); T indicates the surface temperature of the object (°K or °C) and finally Tf indicates the liquid temperature (°K or °C).…”