This paper presents an accurate modeling method to investigate the thermal performance of the windings under steady state. The model considers the heat conduction of active windings and heat convection of end windings. To verify the validity of this model, a 20/24 poles/slots permanent magnet (PM) in-wheel motor is taken as an example. Firstly, the temperature distribution of the active windings in the slot is calculated by a multi-block 2-D temperature field model, which is verified by the model built according to the reality. The numerical results of blocks model agree well with those of the real model. Secondly, a 3-D temperature field model with the end windings is built on the 2-D blocks model. Furthermore, to include the air inside the motor, computational fluid dynamics (CFD) has been utilized, and the numerical results are experimentally verified. Finally, the distribution of the heat transfer coefficient (HTC) of the end windings and the influence of rotor speed on the HTC are investigated. These HTCs acquired from CFD results and empirical formulas are compared and analyzed carefully.

This article investigates the asymmetric temperature distribution of a modular permanent magnet (PM) synchronous in-wheel motor under fault conditions, and based on this, proposes a fault-tolerant (FT) strategy named minimum temperature difference strategy (MTDS) to avoid the high temperature appearing at local winding. First, the modular motor system and the FT principle are introduced, and the reconfiguring fundamental magneto motive force (MMF) under open-circuit of one phase in one module is deduced. Second, the loss and temperature distributions of the motor with normal operation are analyzed by the coupled electromagnetic–thermal method. And the mutual verification between simulation and experiment is adopted to separate the copper losses, iron losses, and PM losses from total losses. Furthermore, the asymmetric temperature distributions of the motor operating with part of modules are analyzed in detail. Finally, the influence of the faulty windings on the temperature of healthy windings is investigated, and the FT strategy of MTDS is proposed. The asymmetric temperature distributions of the motor under various FT strategies are compared. The result shows that the MTDS can significantly reduce the maximum temperature of the windings and makes the winding temperature distribution more uniform.

In-wheel motors, as the core power component of electric vehicles, require not only high power density but also high reliability and fault-tolerant (FT) capability. This article proposes a modular permanent magnet (PM) in-wheel motor and design to receive the high FT performance and low magnetomotive force (MMF) space harmonic. First, according to the working mechanism and main faulty types of the modular FT motor, the corresponding FT control strategies are given, and the slot–pole combination with high FT performance for the modular motor is developed. Second, the electromagnetic characteristics of the modular in-wheel motor are investigated. The relationship between the FT performance and the inductance parameters is linked through the magnetic coupling coefficient. The design requirement for the inductance of this kind of motor is proposed. Third, the torque performance of the motor is studied, and the factors affecting torque performance during fault and FT operations are revealed. Finally, a prototype with a slot–pole combination of 24S16P and four modules is produced, and the electromagnetic characteristics of the motor under FT operations are verified by experiments.

High power density outer-rotor motors commonly use water or oil cooling. A reasonable thermal design for outer-rotor air-cooling motors can effectively enhance the power density without the fluid circulating device. Research on the heat dissipation mechanism of an outer-rotor air-cooling motor can provide guidelines for the selection of the suitable cooling mode and the design of the cooling structure. This study investigates the temperature field of the motor through computational fluid dynamics (CFD) and presents a method to overcome the difficulties in building an accurate temperature field model. The proposed method mainly includes two aspects: a new method for calculating the equivalent thermal conductivity (ETC) of the air-gap in the laminar state and an equivalent treatment to the thermal circuit that comprises a hub, shaft, and bearings. Using an outer-rotor air-cooling in-wheel motor as an example, the temperature field of this motor is calculated numerically using the proposed method; the results are experimentally verified. The heat transfer rate (HTR) of each cooling path is obtained using the numerical results and analytic formulas. The influences of the structural parameters on temperature increases and the HTR of each cooling path are analyzed. Thereafter, the overload capability of the motor is analyzed in various overload conditions.

This paper studies the radial force and vibration performance of the modular three-phase permanent magnet synchronous machine under typical two-phase open-circuit faults: symmetrical and asymmetrical. First of all, the expressions of armature magnetomotive force are formalized in normal and fault conditions; thus, the air-gap magnetic fields and radial force density can be analyzed theoretically. Second, the theoretical analysis is verified by running the finite-element simulation of a four-unit modular machine. The relationship between the fault types and radial force harmonic contents is also discussed with the help of 2-D fast Fourier transform. This is followed by the transient and harmonic structural analysis, with the exciting forces imposed on the stator system in order to get the acceleration response. The simulation results are validated by vibration measurement experiments of a similar small-sized modular motor. This investigation can instruct the designer to lower the modular machine’s vibration under different fault conditions.

This paper presents an analytical method for the calculation of the iron losses in a spoke-type permanent magnet synchronous in-wheel motor. According to the magnetic field distribution, the iron cores are divided into tooth, yoke, bridge, and shoe. Based on the boundary conditions of the subdomain model, the bridge is equivalent to the fan-shaped region with constant permeability. Then, the no-load and on-load magnetic fields in the air gap, tooth, yoke, bridge, and shoe are analytically calculated. The impacts of slotting and bridge saturation are considered. On the basis of the analytical expression of the magnetic fields, the iron losses of the tooth, yoke, bridge, and shoe are obtained by the Bertotti model. The analytical results in the no-load and on-load conditions are compared with that of the finite-element analysis. The validity is verified by the finite-element analysis.