Temperature sensing in electric motors is an important task to ensure component protection against excessive heat while maximizing the power and torque capabilities. In order to optimize the dynamic performance limits of a motor during online operation, important motor temperatures must be known in real time. Since temperature measurements are associated with costs and integration efforts, model-based estimation methods became highly relevant. In recent years, many promising contributions have been made to this field leading to a vast literature basis. This paper organizes the literary landscape and gives a bird's-eye overview of the three most important estimation classes: Indirect methods, which track temperature-sensitive electrical motor parameters, and direct methods, namely lumped-parameter thermal networks as well as supervised machine learning. Practical limitations as well as special challenges of the respective methods are emphasized throughout the text. The aim of the paper is therefore to facilitate the entry for interested researchers and engineers in this field as well as to stimulate new research impulses. Hence, open problems as well as future research questions are addressed at the end of this review.

Thermal Monitoring of Electric Motors: State-of-the-Art Review and Future Challenges

This article focuses on the electromagnetic vibration source and its reduction design in fractional-slot concentrated-windings (FSCWs) permanent magnet (PM) machines. First, the electromagnetic force and vibration characteristics of a 12-slot/10-pole FSCW PM machine are investigated. Then, four electromagnetic vibration sources are investigated and compared, in which the machine operating state is considered. The result shows that the electromagnetic force modulation and stator magnetomotive force (MMF) harmonics are the two sources that contribute most to the vibration underrated and heavy load condition, respectively. Afterward, two new designs to reduce the vibration caused by the electromagnetic force modulation and stator MMF harmonics are proposed, and the reduction principles are described in detail. Finally, the prototypes of the existing and proposed 12-slot/10-pole FSCW PM machines are manufactured. The tests are conducted to validate the theoretical analysis and proposed vibration reduction design. 

Analysis and Reduction of Electromagnetic Vibration in Fractional-Slot Concentrated-Windings PM Machines

Multiphysics modeling and analysis are classic but vital problems for permanent magnet brushless (PMBL) machine design Bulk of studies give analysis but lack modeling guidelines, comparisons, and rational validations Accordingly, the principal objective of this article is to systematically investigate the accuracy and rationality among five proposed multiphysics models Also, it will offer guidelines of modeling and progressive validation for in-depth PMBL machine design optimization from multidisciplinary aspects of electromagnetic, mechanical, vibration, and control A combined mathematical modeling, finite element analysis, cosimulation, experimental coupling methodological approach is carried out As a critical phenomenon, electromechanical vibration necessitates theoretical analysis of modified excitation forces considering inverter-side harmonics Based on a typical spoke-type PMBL machine prototype and tests, the performances under different operation modes are verified, which serve as the prerequisite of vibration prediction Finally, parallel comparisons between multiphysics simulation and experimental results verify the accuracy and rationality of proposed models, and a balance between model complexity and accuracy is thus presented

Exact Multiphysics Modeling and Experimental Validation of Spoke-Type Permanent Magnet Brushless Machines

This paper investigates the electromagnetic force and vibration characteristics of a dual-stator consequent-pole hybrid excitation (DSCPHE) motor for electric vehicles. Firstly, the topology and operation principle of the DSCPHE motor are introduced. Subsequently, the temporal and spatial harmonic characteristics of airgap flux and electromagnetic force are derived and analyzed theoretically. The influences of circumferential-segmented winding, consequent-pole rotor, and excitation modes on radial force harmonics are investigated by finite element analysis (FEA). The vibration behaviors of the DSCPHE motor are investigated by the multi-physics FEA model based on mode superposition method. The radial force harmonics that dominate the motor vibration are analyzed. Finally, the DSCPHE motor prototype is built and tested. The motor vibration behaviors are experimentally measured and compared with an interior permanent-magnet synchronous motor (IPMSM) to validate the theoretical results. This work will contribute to the vibration suppression and optimization of the DSCPHE motor.

Electromagnetic Force and Vibration Study of Dual-Stator Consequent-Pole Hybrid Excitation Motor for Electric Vehicles

This paper describes a simple method of approximating hysteresis changes in electrical steel sheets. This method is based on assumptions that flux density or field strength changes are a sum or a difference of functions that describe one curve of the limiting hysteresis loop and a certain ‘transient’ component. Appropriate formulas that present the flux density as functions of the field strength and those that present inverse dependencies are proposed. An application of this approximation requires knowledge of the measured limiting hysteresis loop and a few minor loops. Algorithms for determining changes in the flux density or field strength are proposed and discussed. The correctness of the proposed approximation of hysteresis changes was verified through a comparison of measured hysteresis loops with the loops calculated for several different excitations of the magnetic field occurring in dynamo and transformer steel sheets. Additionally, an example of the application of the proposed approximation of hysteresis changes is discussed in the paper. The proposed approximation of hysteresis changes is recommended for numerical calculations of the magnetic field distribution in dynamo and transformer steel sheets.

https://www.mdpi.com/1996-1073/14/14/4110/pdf

Approximation of Hysteresis Changes in Electrical Steel Sheets

This article aims to disclose the negative effect of bread-loaf magnet on vibration performance in fractional-slot concentrated-winding (FSCW) permanent magnet synchronous motors (PMSMs). First, the initial phase relationship in PM flux density harmonics is clarified. Then, the effect of bread-loaf magnet on electromagnetic force, including radial and tangential components, is investigated, in which the force modulation effect is considered. Bread-loaf magnet greatly weakens PM flux density harmonics. However, the dominated electromagnetic force generated by these weakened PM flux density harmonics has an opposite phase angle to that of the synthetic one. As a result, the bread-loaf magnet has a negative effect on reducing the dominated electromagnetic force component. Afterward, two 12-slot/10-pole FSCW PMSMs with conventional and bread-loaf magnet are used to evaluate electromagnetic force and vibration response. It is found that the bread-loaf magnet significantly increases the electromagnetic force and vibration response in the FSCW PMSM. Finally, two 12-slot/10-pole FSCW PMSMs with conventional and bread-loaf magnet are manufactured and tested to validate the theoretical analyses.

Investigation of Bread-Loaf Magnet on Vibration Performance in FSCW PMSM Considering Force Modulation Effect

In this article, a new equivalent thermal network (ETN) model for surface-mounted permanent magnet machines is proposed by applying a mesh-based method with bidirectional coupled winding solution. The key is to couple the winding temperature distributions with thermal network meshes in stator dynamically. First, the meshing method is proposed and combined in the lumped parameter thermal model to obtain temperature distributions instead of the average temperature. The mesh elements have identical shapes and unified thermal conductivity, which can greatly enhance the modeling flexibility and efficiency. Second, the slot winding is established by a 2-D analytical solution method under segmented boundaries with a temperature gradient. Then, the winding solution is coupled with mesh nodes and integrated in the ETN model to accurately predict the temperature distributions in slot including the maximum temperature and position offset. Finally, the effectiveness of the proposed ETN model is verified by comparison with the finite-element analysis and experimental results.

A Generalized Mesh-Based Thermal Network Model for SPM Machines Combining Coupled Winding Solution

This paper investigates the effects of eccentric magnet design on sideband electromagnetic force (SEMF) and hence high-frequency vibroacoustic performance of integral-slot surface-mounted permanent magnet (SPM) machines. Also, the tangential SEMF components are considered to investigate their contribution for high-frequency vibration and acoustic noise. Firstly, the mechanism of sideband current harmonics introduced by space vector pulse-width modulation technique of open-winding drive system is derived. Moreover, the critical components of sideband synthetic magnet field in air-gap are derived to obtain the radial and tangential SEMF density components, and the effects of concentric magnet design of that is discussed. Then, the vibration synthesis model and acoustic radiation model are used to predict the vibroacoustic performance of machines. The results shows the eccentric magnet design can reduce the high-frequency vibration and noise of integral-slot SPM machines. Finally, two integral-slot SPM machines with concentric and eccentric magnets are manufactured and tested to validate the theoretical investigations.

Effects of Eccentric Magnet on High-Frequency Vibroacoustic Performance in Integral-Slot SPM Machines

This article proposes a mesh-based magneto-electric coupling network model for prediction and reduction of permanent magnet (PM) eddy current loss in a flux-switching permanent magnet machine. The key is to couple the electromagnetic inductions between the eddy current network and the equivalent magnetic network (EMN) in stator PMs dynamically. First, the eddy current networks of PMs are established with electric meshes. The electromotive forces of electric mesh are induced by considering double-side effects based on Maxwell's equations. Second, the stator meshing method is propose with PM segments, and combined in the EMN matching to the eddy current mesh. High efficiency and accuracy with detailed magnetic field distributions can be obtained. Then, the magnetic fields generated from EMN PM nodes are coupled in eddy current network to accurately predict the flow directions and density distributions. Finally, the original design and two other structures with rotor magnetic barriers are analyzed for reduction of eddy current losses. The effectiveness of the proposed model is verified by finite-element analyses and experimental results.

Magneto-Electric Coupling Network Model for Reduction of PM Eddy Current Loss in Flux-Switching Permanent Magnet Machine

The invention relates to a 2D magnetic circuit subdivision modeling method for a stator and rotor double permanent magnet cursor motor, which comprises the following steps: dividing a complex magneticfield region and a regular magnetic field region of the motor, and performing diamond small mesh subdivision and magnetic circuit permeance equivalence on the two regions respectively; improving theconnection relationship of permeance nodes at the boundary of the two types of regions to construct a complete 2D magnetic circuit division model, and establishing permeance solution matrix equationsin turn; constructing a relational formula between a permeability convergence factor and the maximum difference of the magnetic density of the motor tooth part; solving the permeance matrix equation,using an iterative algorithm to realize fast solution of the matrix to obtain the magnetic flux and magnetic potential of each permeance node, and further calculating the magnetic flux density and permeability of each permeance; and calculating the electromagnetic parameters such as the flux linkage of each phase, counter electromotive force of the winding of the motor and the like according to the electromagnetic calculation constraint of the motor, and finally comparing with the result of a finite element. For the first time, the 2D magnetic circuit subdivision modeling method for stator androtor double permanent magnet cursor motor in the present invention performs 2D magnetic circuit subdivision for a stator and rotor double permanent magnet cursor motor, and the provided scheme can provide reference research for this type of double permanent magnet motor.

Tong Liu

Papers

Investigation of Bread-Loaf Magnet on Vibration Performance in FSCW PMSM Considering Force Modulation Effect

A Generalized Mesh-Based Thermal Network Model for SPM Machines Combining Coupled Winding Solution

Effects of Eccentric Magnet on High-Frequency Vibroacoustic Performance in Integral-Slot SPM Machines

Magneto-Electric Coupling Network Model for Reduction of PM Eddy Current Loss in Flux-Switching Permanent Magnet Machine

2D magnetic circuit subdivision modeling method for stator and rotor double permanent magnet cursor motor