Thermal Management Of Electrical Machines Research Articles

Thermal management of electrical machines for propulsion – challenges and future trends

Thermal management of electrical machines for propulsion – challenges and future trends

Analysis of power loss in heat pipes for integrated thermal management of next generation electrical machines

This paper presents analysis of eddy-current power loss in heat pipes (HPs) for integrated thermal management of electrical machines. Here, a close integration of HPs with winding body is considered. Such an arrangement is particularly attractive, as it targets the main heat source within the machine assembly. However, there are several challenges associated with the subsystem compatibility, which include electromagnetic, thermal, and mechanical design aspects. The HP’s power loss, which is generated as a results of the time varying stator and/or rotor slot magnetic flux leakage, requires careful considerations. Although, the HP-enabled thermal management of electrical machines (electrical windings) has been previously investigated, the additional HP generated power loss has had a very little attention. In this work, the author proposes alternative techniques for accurate predictions of HP generated power loss accounting for the HP’s wick structure. Three alternative custom-built HP constructions Copper-Water and Titanium-Water with sintered and mesh wicks have been investigated in this analysis. Both theoretical finite element (FE) electromagnetic and experimental methods are discussed in detail. The results show that the proposed experiment informed FE model of HP with an equivalent electrical resistivity wick region provides an accurate HP representation useful in design of electrical machines. Further to these, the proposed approach is demonstrated on an example custom vapor chamber (VC) highlighting the importance of accurate power loss predictions in HPs and VCs.

Heat pipe based thermal management of electrical machines – A feasibility study

In this paper the use of off-the-shelf heat pipes (HPs) are assessed for the thermal management of electrical machines. The stator-winding assembly has been selected to assess the suitability and effectiveness of cooling systems based upon HPs. The proposed approach targets the main heat source in electrical machines, which is generally associated with the winding subassembly. Two thermal management systems are investigated from a conceptual point of view. The first one uses HPs to improve heat removal for a machine with conventional cooling, e.g. a liquid or air-cooled housing. The second variant uses HPs as the main heat transfer route, e.g. a fully enclosed machine with no integrated, actively cooled housing. Both active- and end-winding regions are considered for direct heat removal from the winding body using HPs. The analysis of the electromagnetic and thermal compatibility of the proposed HP-based thermal management systems is via three-dimensional (3D) finite element analyses (FEAs). It is theoretically shown that the winding active region is better suited for effective HP-based thermal management, compared with the end-winding alternative. Also, the results suggest that proposed thermal management systems allow for a considerable improvement in heat removal from the machine body, up to 43% and 25% for the concepts one and two respectively (applied to the winding active region) respectively, as compared with a more conventional heat removal system. The overall performance gains of course depend upon the specific manufacture and assembly processes used in construction of the stator-winding. The initial results from tests on the hardware subassemblies confirm validity of the theoretical methods employed in this feasibility study.

Thermally conductive polymer composites for thermal management of electric machines: A modeling and experimental study

With ever-increasing drive to improve the power output of electric machines and reduce heat accumulation based insulation failure, efficient thermal management is highly desirable. Increasing thermal conductivity of impregnation resin is critically important for thermal dissipation in electric machines. In this work, we investigated how the improvement in thermal conductivity of impregnation resins could benefit the heat dissipation of electric machines. To this end, a two-dimensional (2D) finite element analysis (FEA) was conducted, which revealed that increasing the thermal conductivity of impregnation resins to 0.6–0.8 W·m−1·K−1 could significantly decrease the winding temperature. Meanwhile, epoxy-based composites with different thermally conductive fillers were synthesized. The effect of filler type/loading on thermal conductivity and viscosity were investigated. After systematically measuring the thermal conductivity and viscoelastic properties of these composites, a “viscosity-thermal conductivity” correlation was plotted to sort out candidate resin for impregnation trials. In addition, impregnated prototypes comprising enamel wires and both neat epoxy resin and thermally conductive composite impregnation resins were fabricated. Under both natural and forced convection, the epoxy/BN composite resin was shown to be effective in reducing the core temperature of prototype by 9.1–18.6 °C compared with neat epoxy-impregnated prototype. The results indicated that thermally conductive polymer composites had the potential to greatly improve thermal management of electric machines. The findings in this work provide insights and guidelines for future development of thermally conductive impregnation resins.

Advances in Thermal Management Technologies of Electrical Machines

Given the fact that the operation of electrical machines generates various loss components that finally become heat, developing advanced thermal management technologies is essential to control temperature increases and to guarantee safe operations. Meanwhile, the armature winding can stand larger currents when the machines are equipped with advanced cooling systems, which directly improves torque/power densities. This paper aims to provide a systematic review of the latest developments of advanced thermal management technologies of electrical machines. According to different heat dissipation mechanisms, the cooling systems studied in this paper are categorized into five major types: enclosed housing cooling, enhanced conductive cooling, embedded heat pipe cooling, direct oil cooling, and enhanced rotor cooling. The advantages and disadvantages of these cooling systems are researched and compared comprehensively. This study contributes to the revelation of insights on the thermal management of electrical machines and offers good guidance for the thermal management of electrical machines.

Thermal Management in Electrical Machines

Apart from protecting electrical machines from temperature related failures, thermal management of electrical machines is employed in the design phase of electrical machines to achieve higher efficiencies and higher power densities [...]

Cooling Analysis of High-Speed Stator-Permanent Magnet Flux-Switching Machines for Fuel-Cell Electric Vehicle Compressor

Thermal management of electrical machines is an important issue to improve electromagnetic performance, reduce system size and prolong lifetime. Based on the equivalent thermal circuit (ETC) and computational fluid dynamics (CFD) methods, the temperature rise characteristic of a high-speed stator-permanent magnet-type flux switching (HS-SPMFS) machine for fuel-cell electric vehicle compressor is predicted. Firstly, the structural features, key dimensions, material properties and heat generation rate of the HS-SPMFS machine and its cooling system are introduced. Secondly, the ETC model of the machine with a liquid cooling channel is proposed, and the size of the cooling system is preliminarily designed. The influence mechanism of the number, size and flow rate of the water channel on the convective heat transfer area, convective heat transfer coefficient, water head loss and winding temperature rise is revealed. On this basis, combined with the CFD method, the temperature distribution of the machine is studied, and the detailed temperature distributions of each component of the machine are obtained and verified by the ETC method considering the cooling system. Finally, a HS-SPMFS machine prototype is manufactured and the temperature test platform of the prototype is built. The temperature rise behaviors of the machine under different working conditions are tested, verifying the theoretical analysis and the prediction methods.

Opportunities and Challenges of Utilizing Additive Manufacturing Approaches in Thermal Management of Electrical Machines

The additive manufacturing approach is considered a new manufacturing technology method and is evolving dynamically in recent years. It is advancing and achieving as the key enabling technology in a wide range of applications, from medical sciences to the aerospace and automotive industries. This novel approach opens a new path to overcome the conventional manufacturing problems and challenges by providing more design freedom, new ranges of materials, lightweight and complex geometries. According to demands metrics such as lightweight and high power density motors. This offers clear motivation to develop the advanced thermal management method with new materials and a novel additive manufacturing (AM) approach. The paper aims to provide a comprehensive review of all the attempts in various electrical machines' thermal management methods using AM method. It considers the opportunities and challenges that designers are facing while implementing these approaches. Finally, the authors make some comments/forecasts on how the AM could improve the performance and manufacturability of the future thermal management system of electrical machines.

Corrections to “Opportunities and Challenges of Utilizing Additive Manufacturing Approaches in Thermal Management of Electrical Machines”

In the above article <xref ref-type="bibr" rid="ref1" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">[1]</xref> , Figs. 3 and 19 are modified versions of Fig. 18 from the article. Although this source was cited in our article as [6], the captions for these figures are missing the appropriate citation/reference.

Experimental and numerical study of heat transfer characteristics of single-phase free-surface fan jet impingement with automatic transmission fluid

Due to the ever-increasing power density of the advanced electric machines (motors/generators) in electric vehicles and hybrid electric vehicles, thermal management of electric machines has become increasingly critical to permit high power output, enhanced reliability, and miniaturization. The cooling of electric machines is mostly accomplished by depositing fluids or oils directly onto the machine's coil windings to remove the excessive heat. As an efficient approach of direct cooling, jet impingement has been attracting significant attention from researchers and industry due to the high heat transfer rates and large cooling capacity. In this work, we present a study of fan jet impingement of automatic transmission fluid (ATF) on a target surface with a constant heat flux. Experiments were carried out with ATF temperatures varying from 50 °C to 90 °C and flow rates varying from 1 × 10−5 to 2.5 × 10−5 m3/s to encompass potential operating conditions within the automotive transaxle environment. A numerical model of the test section was developed and validated with experimental results and used to investigate the influence of flow parameters and nozzle geometry on the heat transfer characteristics of the impinging fan jet. Major controlling parameters studied in this work include flow rate, fluid temperature, nozzle-to-target distance, and incidence angles. Average heat transfer coefficients are calculated as the major metric to compare the impact from various controlling parameters. Correlation of flow and heat transfer characteristics of fan jet impingement is explored within the scope of this work. In addition, heat transfer coefficient results of fan jet impingement are compared with the circular jet, which is commonly applied to cool electric machines. At all flow velocities, circular jets yield heat transfer coefficients 20%–25% higher than those obtained from the fan jet impingement.

Improved Thermal Management and Analysis for Stator End-Windings of Electrical Machines

In an electrical machine design, thermal management plays a key role in improving the performance and reducing size. End-windings are commonly identified as the machine hot-spot. Hence, lowering and predicting end-windings temperature are crucial tasks in thermal management of electrical machines. This paper proposes and investigates a noninvasive but effective cooling method that aims for a uniform cooling of a machine's winding by implementing direct cooling on its end-windings. Modeling and experimental results show that a 25% hot-spot temperature reduction on a particular application can be achieved. To analyze the proposed technique in detail, an accurate but computationally economic lumped parameter thermal network is developed. Comparison between a “standard” thermal network and its simplified equivalent (with less nodes) is presented where the models are developed and fine-tuned based on experimental data. All the above is used to investigate the potential of the proposed end-winding cooling method with different configurations of the methodology.

Thermal management of electric machines

Electric machines have broadly been used in many industries including the transportation industry. With the evolving trend of electrification in transportation, electric machines with higher power density and higher efficiency are demanded and, thus, more stringent thermal management requirements are needed for electrified vehicle applications. This study comprehensively presents various important aspects of thermal management in electric machines with the main focus on transportation applications. Design considerations, challenges, and methods for enhanced thermal management are discussed. Fundamental thermal properties of common materials are presented and sources of losses in various parts of machines are explained. Furthermore, typical cooling techniques and thermal analysis approaches for electric machines are reviewed in detail. This study will serve as a reference guideline for machine designers, who are interested in thermal management, and for thermal researchers working on electric machines.

Computational fluid dynamics modelling of an entire synchronous generator for improved thermal management

This study is the first in a series dedicated to investigating the airflow and thermal management of electrical machines. Owing to the temperature dependent resistive losses in the machine's windings, any improvement in cooling provides a direct reduction in losses and an increase in efficiency. This study focuses on the airflow which is intrinsically linked to the thermal behaviour of the machine as well as the windage power consumed to drive the air through the machine. A full computational fluid dynamics (CFD) model has been used to analyse the airflow around all major components of the machine. Results have been experimentally validated and investigated. At synchronous speed the experimentally tested mass flow rate and windage torque were under predicted by 4% and 7%, respectively, by the CFD. A break-down of torque by component shows that the fan consumes approximately 87% of the windage torque.

Real-time thermal management of permanent magnet synchronous motors by resistance estimation

Real-time thermal management of electrical machines relies on sufficiently accurate indicators of internal temperature. One indicator of temperature in a permanent-magnet synchronous motor is the stator winding resistance. This study applies two current injection techniques to a commercially produced permanent-magnet servomotor, which are applicable under load and cause minimal disturbance to the shaft torque. The current injection techniques applied here enable the temporary boosting of resistive voltage and consequent application to low-resistance, high-voltage machines. The effectiveness of the approach is demonstrated by tracking the change in winding temperature during a 2 h load cycle.

Methods of Resistance Estimation in Permanent Magnet Synchronous Motors for Real-Time Thermal Management

Real-time thermal management of electrical machines relies on sufficiently accurate indicators of internal temperature. One indicator of temperature in a permanent-magnet synchronous motor (PMSM) is the stator winding resistance. Detection of PMSM winding resistance in the literature has been made on machines with relatively high resistances, where the resistive voltage vector is significant under load. This paper describes two techniques, which can be applied to detect the winding resistance, through “angle” and “magnitude” current injection. Two further methods are described, which discriminate injected current and voltages from motoring currents and voltages: “unipolar” and “bipolar” separation. These enable the resistance to be determined, and hence the winding temperature in permanent-magnet machines. These methods can be applied under load, and in a manner that does not disturb motor torque or speed. The method distinguishes between changes in the electromotive force constant and the resistive voltage. This paper introduces the techniques, while a companion paper covers the application of one of the methods to a PMSM drive system.