Article

A critical review on thermal management technologies for motors in electric cars

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Abstract

The development of electric cars has well been regarded as a major solution for tackling the challenges of carbon-neutrality faced by the modern communities. Electric motor is certainly the core and most important components of an electric car, and the thermal management for electric motors has drawn increasing attention from both industry and academic society. This is because electric motors in modern electric cars are required to be more powerful and competitive with higher torque, higher speed and higher power density, therefore the efficient thermal management has become essential to maintain the motors efficiency, durability and safety. The failure of thermal management will result in demagnetization of magnets, aging of the insulation materials, decrease of efficiency, shorter lifetime and even burnout of motors. To enlighten the future research, in this paper, both the theoretical modeling and experimental investigations of the latest thermal management methods are reviewed. The state-of-the-art of various thermal management techniques, including air cooling (natural and forced air cooling, air impingement cooling) and liquid cooling (water/oil jacket cooling, jet impingement cooling, spray cooling, immersion cooling, slot channel forced convection cooling) for the stator, winding and rotor are critically presented. Meanwhile, heat transfer enhancement methods by conduction based on potting materials, thermal paste, heat guides, PCMs and heat pipes are highlighted. Following that, hybrid thermal management technologies to address extreme conditions are also discussed. In the last section, some suggestions are given for future possible research and applications. The paper is expected to be a good reference and inspiration for the development of new thermal management concepts of electric motors.

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... In recent years, with phenomenal progress in the technology of cooling materials and manufacturing tools, highly effective strategies have been investigated to mitigate the temperature of electric motors [11]. Creating a coolant flow through a centrifugal pump in a cooling jacket is the most efficient and straightforward way to decrease the temperature of motor components, where the location of cooling jackets determines the effectiveness of the cooling [12,13]. In an indirect cooling configuration for a 60 kW , 4000 r:p:m axial flux PMSM, ref. [14] proposed a casing-embedded spiral cooling jacket, in which the temperature reduction of the stator side is through the conduction heat transfer from its elements to the cooling channels and then convection through the coolant fluid. ...
... When the residual value of the solution in the energy equation is 10 − 6 , and for the solution of the turbulence, momentum, and continuity equations is 10 − 3 , it is judged as converged. (5)- (12) according to the flowchart of numerical study in Figure 9. Firstly, the 3-D models of solid and fluid parts are designed, and the region of solution is discretised through meshing. Subsequently, the material properties are set in the solid and fluid region according to Table 3, and the initial and boundary conditions of the fluid region are determined. ...
Article
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Permanent magnet synchronous motors (PMSMs) experience considerable performance degradation due to the rise in temperature and the resulting partial demagnetisation in the PMs, as well as the shortenings in the insulations' lifetime. To mitigate the temperature of motor components, it is crucial to investigate and continually improve the design of efficient cooling systems. This study implements the water immersion cooling (WIC) concept on a surface‐mounted PMSM (SMPMSM), where through comparing its cooling performance with the forced ventilation cooling (FVC), it is indicated that, even at high inlet velocities for the latter, it cannot maintain the temperature below the specified thresholds and the required input electric power to run the ventilation fan will be increased exponentially to compensate for its ineffectiveness. While in the WIC configuration, the winding and PM temperature values remain well below the margins when the heat transfer coefficient of this method is 40% %\% higher than the FVC. By incorporating the effect of the cooling process through the heat transfer coefficient, the lumped‐parameter thermal network (LPTN) is utilised to study the operation mode of the motor under the mentioned cooling configurations. Besides achieving higher cooling efficiency, the WIC strategy can quickly reduce temperature, which is reflected in the thermal time constant of the cooling method extracted from the LPTN. Consequently, it is demonstrated that up to 35% %\% higher than the nominal generated heat, the SMPMSM under the WIC can operate continuously, while for the FVC, the frequent start‐stop driving scenario should be employed.
... The heat transfer depends on air circulation velocity and must be calculated by combining natural and forced convection. The circulation velocity of air inside the motor depends on the frequency of the rotor and can be shown as [28]: ...
... It should be noted that R744 has the best values ( Figure 11). For coolant temperatures of +10 °C, the temperature increases from 81. 28 ...
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This article presents modeling results and a comprehensive analysis of evaporative cooling systems designed for electric motors using the refrigerants R744 (trans-critical), R134a, R600a, and R290. This study aims to determine the most suitable refrigerant for use in a cooling system, optimize the system design, and calculate the maximum achievable motor power while adhering to specified temperature constraints. The modeling was validated by an experimental setup, which had the cooling system’s configuration featuring three circuits for motor housing, stator, and rotor cooling, respectively. The modeling of an evaporative system was used to present the cooling efficiency under varying loads and external temperature conditions. Mathematical modeling encompasses complex algorithms to simulate heat transfer phenomena, accounting for fluid dynamics and refrigeration cycle dynamics. The analyses revealed trends in winding temperature, rotor temperature, air temperature inside the motor, heat transfer coefficient, coefficient of performance (COP), and motor power across different operating conditions while using different cooling refrigerants. The maximal heat transfer coefficients were calculated for all the refrigerants for winding temperatures in the range from 32 to 82 °C, while air temperature and rotor temperatures were between 42 and 105 °C and 76 and 185 °C, respectively. Lowering the evaporation temperature of the coolant to −35 °C resulted in a significant decrease in the winding temperature to 15 °C, air temperature to 38 °C, and maximum rotor temperature to 118 °C at a motor power of 90 kW. Refrigerant R744 emerged as a promising option, offering high heat transfer coefficients and achieving high motor power within temperature limits. At the same time, the COP was lower when compared with other working fluids because of the high ambient temperature on the gas cooler side.
... Due to their superior output power per unit weight or volume, there is an increasing demand for high-power density motors in various vehicle applications, including electric vehicles, electrified aircraft, rail transportation, and maritime applications [1][2][3][4][5]. According to the definition of motor power density, there are two potential avenues for enhancing motor power density: firstly, by augmenting its output capacity through improving its cooling efficiency [6][7][8]; and secondly, by reducing the weight or volume of the motor. ...
... (1) Motor weight reduction: 20.27%~30% [11,31] (2) Shaft weight reduction: 50% [16] (1) Low thermal conductivity (2) Limited mechanical strength Aluminum windings [35][36][37] Aluminum alloys (1) Motor weight reduction: 9%~10% [35,36] (2) Slot fill factor: 75%~83.8% [35][36][37] (1) High resistivity (2) The impact on the reliability of the wire insulation layer Soft magnetic composites [41][42][43] High purity and compressibility of iron powder (1) Power per unit volume: 526~673 kW/m 3 [41] (2) Efficient: 78%~88% [41][42][43] (1) Low permeability and high hysteresis loss (2) Low mechanical strength Superconducting materials [46][47][48] YBCO, REBCO ...
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The demand for high-power density motors has been increasing due to their remarkable output capability and compact construction. To achieve a significant improvement in motor power density, lightweight design methods have been recognized as an effective enabler. Therefore, extensive investigations have been conducted to reduce motor mass and achieve lightweight configurations through the exploration of lightweight materials, structures and manufacturing techniques. This article provides a comprehensive review and summary of state-of-the-art lightweight implementation methods for electrical machines, including the utilization of lightweight materials, structural lightweight design, and incorporation of advanced manufacturing technologies, such as additive manufacturing techniques. The advantages and limitations of each approach are also discussed in this paper. Furthermore, some comments and forecasts on potential future methodologies for motor lightweighting are also provided.
... Modern automobiles have about 100 different kinds of electric drives [14], however only six possible machines for EV propulsion are considered here (Fig. 1): ...
... Modern automobiles have about 100 different kinds of electric drives [14], however only six possible machines for EV propulsion are considered here ( of the initially developed motors used in EVs due to its appropriate management, strong torque at low speeds, dependability, simple control system, and low cost [15]. It could be a viable choice for an EV powertrain [16]. ...
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Utilizing electric vehicles (EVs) in place of conventional vehicles is now necessary to lower carbon dioxide emissions, provide clean energy, and lessen environmental pollution. Numerous researchers are trying to figure out how to make these electric vehicles better in order to address this. Electric motors and batteries are necessary parts of electric cars. As such, the development of these vehicles was associated with the development of these two entities. This review lists all of the sophisticated electric machines, their control schemes, and the embedded systems that are utilized to put these schemes into practice. Due to this review, we determined out, the induction motor and permanent magnet synchronous motor have been demonstrated to be the most efficient and suitable alternative for propulsion drive in electric vehicles. Furthermore, because torque and speed can be controlled simultaneously with minimal noise and ripples, the FOC approach continues to be the ideal control method. This evaluation offers comprehensive information regarding the application of various control measures. Whereas the model-based design technique made it easier for engineers to program, validate, and fine-tune the system's controllers before deploying it in the field, STM32 and DSP320F28379 are the best embedded systems for implementation because of their low cost and compatibility with the SIMULINK environment.
... Extensive research in electric vehicles' thermal management has been targeting the component level. Multiple review articles are available on the thermal management of battery systems [9][10][11][12], electric machines [13][14][15], power electronics [16][17][18], and fuel cell systems [19]. However, sustainable solutions for electromobility with electric vehicles are not only about batteries, power electronics, and electric machines. ...
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Electric vehicle thermal management systems have in the last two decades grown to become complex systems. This development has come as a response to the unique challenges faced by electrified powertrains, particularly the driving range reduction in cold climate operation. The rapid increase in complexity makes the systems harder to design, control, and evaluate, and consequently, a need for systematic analysis and design tools has emerged. The key contribution of this work is a model-based simulation tool developed to enable the combined evaluation and control of state-of-the-art thermal management systems. To show how engineers may use the tool to solve industrially relevant problems, two simulation case studies are performed and presented. The first case study compares three thermal management system layouts of increasing complexity and shows how their performance varies as ambient temperature decreases. The second case study concerns the potential benefits of additional cooling radiators for fuel cell trucks under heavy load in hot climates.
... Due to the longer thermal path [11], the heat extracted is lower in the indirect cooling, than the direct one, therefore, they are less compact and the torque density capability is restricted. However, direct cooling strategies has superior costs and manufacturing challenges [12]. ...
... Consequently, liquid-based cooling systems are preferred for this type of application, thanks also to the higher specific heat and convective coefficient of liquids compared to gaseous coolants [23]. These systems may be designed in many different ways, according to the type of liquid (dielectric properties), the cooling strategy (direct or indirect), and the position of the hotspot inside the motor (stator, windings or rotor). ...
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The on-the-road transportation sector is living a strong transition era, shifting from a technology massively based on internal combustion engines (ICEs) toward electric powertrains. Even though the electrification of vehicles as it is presented today still deserves an in-depth analysis for many reasons not only technological, a share of pure electric vehicles in the future will be present on the market, but reoriented to an urban use where a strong reduction of the harmful pollutants is needed. Within this aim, the improvement of the electric motor reliability, operability, safety, continuity of operation, and peak power delivery as well as the integration of them into the powertrain with the ICE technology is particularly required. Electric motor thermal management influences all the mentioned aspects. Electric motor cooling is usually realized with cooling jackets inside the stator. However, when the specific power (kW/m ³ ) increases (as it is needed for the automotive electric traction), the rotor also requires an intensive cooling introducing some additional complexities. This can be done by cooling the shaft of the rotor via a dedicated inner fluid circulation contributing to keep the electric motor performance closer to the rated conditions. In this paper, a liquid cooling of the shaft on an electric traction motor has been studied thanks to a Computational Fluid Dynamic (CFD) model and under variable boundary conditions. The cooling can be realized with a double concentric tube in the shaft: the first is fixed, and the second one rotates with the rotor. This concept requires a dedicated mechanical sealing system which ensures fluid sealing. The model has been used to enhance the heat transfer coefficient in order to approach rotor temperature to the one of the cooling fluids. With reference to different operating cooling conditions and designs, the temperatures of the rotor have been predicted also considering different fluids, and geometrical design choices of the cooling double pipe. The proposed design solution reduced the rotor temperature by 30°C compared to a baseline rotor cooling system represented by a simple direct-through cooling passage.
... The primary heat sources in electric machines are the losses in the copper and iron components [7]. High temperatures in electric motors can lead to demagnetization of the magnets [8], insulating material damage [9], decreased efficiency [10], shortened motor lifespan [11], and potential motor burnout [12]. An increase in the temperature of a motor leads to an escalation in the resistivity of copper. ...
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Electric vehicle (EV) proliferation is accelerating, characterized by the rising quantity of electric automobiles on global roadways. The electric machine is a crucial component of an EV, and the heat generated within the motor requires consideration as it impacts performance and longevity. A prevalent form of machine in EV is the in-wheel motor (IWM), which is notable for its compact size. However, it presents more significant cooling challenges. This research offers a new cooling method to cool the IWM. The system consists of wafters mounted on the housing of the IWM. Testing was conducted to determine the effect of wafters on the thermal properties and performance of IWMs. The machine used in this research is a brushless direct current (BLDC) motor featuring an outer rotor configuration and a peak power output of 1.5 kW. Testing was carried out experimentally and by simulation, and the simulation used Ansys Motor-CAD software. The research results show that applying wafers to IWM reduces the temperature of IWM components by up to 13.1%. IWM with wafters results in a torque increase of 0.14%, a power increase of 0.64%, and an efficiency improvement of 0.6% compared to IWM without wafters.
... The thermal characteristics of the airgap are critical as the thermal connection between the stator and rotor is through this narrow region. The circulating flow in the smooth annular airgap subjected to inner cylinder rotation is considered completely radial flow with an equivalent thermal conductivity, which is calculated based on (13) to consider the self-ventilation effect of the rotor rotation on the temperature [47,48]. ...
Article
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Severe temperature rise is not tolerated in the windings and permanent magnets (PMs) of the electric motors due to the resultant performance degradation, increased maintenance cost, and eventually the short-circuit faults. This article suggests a new approach to mitigating the temperature of components in a flux-switching PM (FSPM) motor using the concepts of heat transfer paths and heat flow diagrams. Accordingly, changing the location of the armature windings from the adjacency of the PMs to the middle tooth of the E-core stator blocks brings multiple thermal and electromagnetic merits to the proposed motor. In the heat generation stage, the numerical studies indicate that the total power losses of the motor decreases from 56.6 W to 39.6 W. Moreover, the maximum working temperature of the windings and PMs is cut by 36.4% and 40%, respectively, demonstrating the remarkable effect of the proposed strategy on temperature. From the electromagnetic point of view, the proposed motor outperforms the E-core FSPM motor due to the separation of the electrical and magnetic loading sources, resulting in the uniformity of the steel cores' flux density. Lastly, the thermal and electromagnetic experimental studies are provided to verify the outcomes of the analytical and numerical investigations.
... The flow in the airgap is laminar when < , and the equivalent thermal conductivity can be selected approximately equal to the thermal conductivity of air under atmospheric conditions. Otherwise, it is turbulent, and the equivalent thermal conductivity, is calculated by (6), where is a constant based on geometrical dimensions [57,58]. It is evident that the effect of rotor rotational speed is applied through the Reynold number, and therefore, the self-ventilation effect is considered. ...
Article
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When electrical machines operate without a specific cooling system, the surrounding environment plays a crucial role in the rise of temperature and the duty cycle of operation. More clearly, a natural convection cooling system with a low value of heat transfer coefficient carries the risk of thermal breakdown, insufficient safety, and reliability. This paper studies the heat transfer aspects of a low-power flux switching permanent magnet (FSPM) motor under natural convection cooling to implement a novel real-time sensor-less temperature monitoring system. Thermal and electromagnetic experiments are carried out to create foundations for transient and steady-state numerical models. A data-driven, deep learning algorithm estimates the core and permanent magnet (PM) eddy current losses in real-time, besides the already available copper and friction losses. Subsequently, a two-node thermal equivalent circuit in a hybrid model with a feed-forward neural network estimates the dynamic temperature profile of windings and PMs. It is indicated that the worst-case estimation error is below 7.5%, and the configuration is applicable under a wide range of operation states and environmental conditions. Lastly, the system, including the power source, FSPM motor, and hybrid temperature estimation unit, will be implemented in MATLAB/Simulink to investigate the fault prediction and operation management capabilities.
... The core losses can be estimated analytically, or most commercial software can calculate them during post-processing. The critical challenges in accurate CFD thermal modelling and numerical analysis are calculating or estimating the thermal transport properties of the solid components for heat conduction and evaluating the heat transfer coefficient at the end space and air gap for convection heat transfer [38]. A comparison study between finite element (FEM) and CFD analysis shows that CFD conjugate heat transfer analysis is more accurate than FEM thermal analysis for predicting the temperature distribution in the windings and other components of an axial flux wheel hub motor [39]. ...
Article
An experimental and 3D CFD (computational fluid dynamics) based numerical investigation of the in-wheel hub internal permanent magnet synchronous machine (IPMSM) has been carried out to understand the thermal dynamics associated with the power loss within the motor. This study can serve as a clear case baseline for the future development of thermal management systems in micro-powertrain systems. Experimental results show that the maximum winding temperature of 65.9 °C has been observed on the end-windings (EW) for an operating condition of 500 rpm (base speed), 4.5 Nm. Stretching beyond this operating point would increase the winding temperature beyond 65.9 °C, potentially damaging the winding insulation’s capabilities and magnetic properties of the permanent magnets (PMs) and adversely affecting the performance of the wheel motors. The hysteresis and eddy current loss coefficients for the stator core have been identified as 14.5 x10e-2 and 1.6 x 10e-4 respectively. The experimentally identified losses have been distributed among the motor components for the development of the numerical thermal model in commercial CFD software Star-CCM+™. The CHT (conjugate heat transfer) thermal paths show that 68.4 % and 31.4 % of the total power loss from the stator components undergo convection and conduction, respectively. This indicates that convection heat transfer dominates on the in-wheel hub IPMSM motor topology. Almost 34.5 % of the heat loss is transferred radially through the air gap to the Permanent Magnets. When the air gap size decreased by 80 %, the amount of convection heat transfer through the air gap increased by a factor of 2 (69 %) and reduced the winding temperature by 13 % (57.3 °C).
... However, higher power ratings inevitably lead to a greater thermal load on the motor's windings and push the insulation towards its thermal limits [5]. Therefore, an effective thermal management becomes crucial [6]. According to [7], the lifetime of the commonly used insulation materials will be halved if the temperature increases to an additional 10°C. ...
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Accurate prediction of winding insulation degradation path is critical for preventing catastrophic equipment failures and optimizing maintenance schedules in electric motors (EMs). Existing methods, such as those based on monitoring high-frequency electrical parameters, often rely on point estimates and neglecting the inherent uncertainties associated with real-world degradation processes. This paper proposes a novel approach utilizing Gaussian Process Regression (GPR) to address this limitation. Building upon recent advancements in high-frequency electrical parameter monitoring in which identifying inter-turn insulation creep is a key degradation indicator, this work adopts GPR to predict the degradation path. GPR offers a powerful framework for incorporating uncertainty quantification into the prediction process. It not only excels at interpolation within the observed data range but also provides a distribution of possible future degradation values. This probabilistic approach acknowledges the variability present in both real-world measurements and the inherent process variability of insulation degradation. The prediction results from proposed GPR-based approach are compared to a nonlinear Wiener-processbased model as a conventional method, and a state-of-the-art optimization algorithm. The estimation accuracy in the worst case scenario of the proposed method gives an error of 0.7% which is more accurate than 4.2%, and 50% resulted from the Wiener-process-based model and the commercial optimization solver respectively. These results demonstrate a significant improvement in estimation accuracy by effectively handling both data and process-related uncertainties.
... At the same time, due to the limitation of the radial size of the casing in the slimhole wells, the outer diameter of the motor housing is small, the internal space of the motor is narrow, and the structure is compact, which is more unfavorable for heat dissipation. In addition, the high-speed rotation of the rotor inside the motor can lead to increased losses such as oil friction and core loss [13,14], which in turn increase the heat production of the motor. Based on the above, SHS-PMSM are prone to high temperature rise. ...
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The small-diameter high-speed submersible permanent magnet synchronous motor (SHS-PMSM) is essential equipment for rodless oil and gas extraction in slimhole wells and high-water content oil wells. The SHS-PMSM typically operates for extended periods of time underground in high temperatures. Because of its compact size, the heat is difficult to dissipate, which increases the risk of motor overheating and damage. In order to accurately predict temperature, the method of magnetic-heat-flow multiphysics bidirectional coupling is studied in this paper. A SHS-PMSM with an outer diameter of ø89mm is taken as the object, and its copper loss, friction loss and convective heat transfer coefficient are studied by analytical derivation. The relationship between them and temperature are expressed by functions which can be compiled into User-Defined Functions (UDFs) as variable during the calculation process of finite volume method. Both coupling calculations and experiments are conducted. The temperature calculated by magnetic-heat-flow bidirectional connection is higher than that produced by the conventional method and more in line with experimental results after the results of both simulations and experiments are carried out and compared. The accuracy of the magnetic-heat-flow bidirectional coupling method is verified and the design basis of temperature for SHS-PMSM can be provided.
... Temperature, particularly within critical components such as rotor magnets, windings, and bearings, significantly influences motor performance, safety, and lifespan. However, traditional thermal management techniques often rely on sensors placed away from the crucial components, leading to latency and imprecise observations of temperature dynamics [18]. ...
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... The fluxes by convective heat transfer serve as the boundary condition for the conductive heat transfer models. 3D finite element models (FEM) offer detailed results but demand long computation times, complex mesh setup and are not suitable for real-time simulations [3]. Lumped parameter thermal networks (LPTN) offer a practical solution through simplified approaches. ...
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... As electric vehicle technology becomes more and more mature, its advantages such as low energy consumption are becoming more prominent and it will gradually become one of the commonly used means of transportation in daily life [1]. Permanent magnet motors have the advantages of high efficiency and high power density and are widely used in electric vehicles. ...
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This paper describes the thermal modelling of a permanent magnet alternator (PMA). The principal focus is to investigate the effect of adding thermal paste into the machine end winding region. A thermal lumped parameter network is proposed to quantify the change in heat flow paths for a flange mounted alternator. The thermal model is implemented in Simulink, which allows many different heat paths to be easily combined. Since addition of a thermal paste introduces new axial heat flow by conduction paths between the stator windings and frame, the developed thermal network considers the detailed heat flow paths in the PMA. The thermal network is extended to the machine frame and part of the mounting plate. It is shown that axial heat flow has been improved 5.6% for the PMA with addition of the thermal paste. This in turn reduces winding temperature by around 10.5% at standstill DC tests. The model accuracy has been validated by performing FEA thermal simulations and experimental results.
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Convection coefficient in the end-winding is a critical thermal parameter in Lumped Parameter Thermal Network (LPTN) model solution for an accurate motor winding temperature prediction. However, it is a challenging task to determine this convection coefficient due to complex heat and air circulation characteristics in the end-winding region. Until now, all researches focus on Totally Enclosed Fan-cooled (TEFC) Aluminum Rotor Induction Motor (ARIM) with a rotor having fins on its end-rings. But Copper Rotor Induction Motor (CRIM) has a rotor that does not have any fins on its end-rings. Hence, this research will determine convection coefficient in the end-region of Copper Rotor Induction Motor (CRIM) that has smooth rotor end. A Computational Fluid Dynamic (CFD) technique along-with a Lumped Parameter Thermal Network (LPTN) model is proposed to determine this convection coefficient. Thermal experiments on a 20-hp Copper Rotor Induction Motor (CRIM) are conducted to validate this proposed approach.
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This paper presents a switched reluctance motor (SRM) torque ripple reduction strategy with deadbeat current control and active thermal management. In this method, the SRM torque is indirectly controlled by the phase current. A deadbeat current control method is used to improve the SRM phase current control accuracy, so that SRM torque control error can be reduced significantly. According to the online measurement of the power switching device temperature, the switching frequency will be reduced to prevent the SRM power converter from being damaged by over-temperature. The feasibility and effectiveness of the proposed strategy have been verified in both simulation and experimental studies.
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The electric motor market has witnessed a major change in the last decade in several aspects: in structure, with company mergers contributing to a more global market, in content with energy-efficiency policies, and in its economy due to increasing electricity prices, all aspects contributing to push the market towards more energy-efficient electric motors. Additionally, the growing market penetration of Variable Speed Drives (VSD), introducing large energy savings in systems with variable loads, was accompanied by a growing concern over their operating efficiency in full and especially in part-load, as well as in stand-by mode. A Motor Driven Unit (MDU) consists of the core components of a motor system: electric motor, variable speed drive (VSD), mechanical transmission and end-use application, like a pump or fan. Regulating the entire Motor Driven Unit (MDU) would translate into 1400 TWh of cost-effective electricity savings (7% of the World motor systems electricity consumption), with a corresponding reduction in emissions of 469 Mton of CO2eq by 2040. Even larger potential energy savings can be made available by the optimization of the entire motor systems, which translates into 3100 TWh of global electricity savings by 2040. Still to date, Minimum Energy Performance Standards (MEPS) have been mostly targeted at individual components only. Difficulties arise in the standardization of measuring and classifying the entire MDU but the larger energy savings achievable by the motor system is leading to the launch a combined system standard by the International Electrotechnical Committee (IEC) and the International Organization for Standardization (ISO). MEPS and standardization at the component and MDU level must be carefully complemented to achieve the maximum energy savings and carbon emission reductions. This paper carries out novel technical, economic and environmental analyses of introducing new policy measures (standards and MEPS) for both individual components and MDUs.
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This paper investigates a new heat extraction approach in application to the high-specific-output electrical machines. The proposed technique employs thermally conductive heat guides (HGs) to provide supplementary heat evacuation paths for the machine regions, which are particularly susceptible to high power loss. Here, the research focus has been placed on the stator-winding assembly. The HGs investigated in this work rely solely on conductive heat transfer, in contrast to the solutions involving working fluid phase change, e.g. heat pipes (HPs). It is intended for the HGs to be an integral part of the stator-winding assembly, e.g. HGs incorporated in the winding active and/or end region. Such arrangement however, imposes several design challenges. These are related with the HGs being a source of additional power loss due to the machine's magnetic flux leakage. The objective of this study is to evaluate a concept of HGs, which are immune to the external magnetic field with good heat transfer capability. To facilitate that, a combination of detailed multi-physics design-optimization together with modern additive manufacturing (AM), i.e. selective laser melting (SLM) method, has been employed here. A number of stator-winding hardware exemplars (motorettes) incorporating alternative HGs designs have been fabricated and tested. This paper provides a new set of experimental data in support of the authors' initial work on HGs' thermal behaviour. The new research findings show that the optimised HGs allow for up to 85% improvement in dissipative heat transfer from the winding body and insignificant additional power loss, for the analysed stator-winding assembly
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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.
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Hairpin windings are gaining increasing popularity in recent years due to their advantages in improving electrical machine performance while reducing manufacturing time and costs. Their geometrical features introduce new challenges and opportunities on thermal management. In particular, spray cooling is increasingly being used, since hairpin windings open up regular and accurately defined gaps in the end-windings compared to the traditional random windings. To date, technical literature on the effectiveness of spray cooling with hairpin windings is lacking, with no practical guidelines available to researchers. In this research, taking an existing hairpin-wound stator, a test rig is developed to investigate the cooling ability of different spray cooling setups on the end-windings. Three types of commercial spray nozzles are chosen to carry out a series of experiments, varying the oil flow rate, pressure, outlet velocity, and number of nozzles. The winding temperature and heat transfer coefficients are presented and discussed. Furthermore, the efficiency of spray cooling is reviewed based on the experimental results. Finally, suggestions on designing similar cooling setups and increasing the cooling efficiency are also provided.
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Modeling of electrical machines is a multiphysics problem. Depending on the phenomena of interest and the computational time constraint, this can be done at different levels of detail. In this paper, the main approaches to model the thermal behaviour of electrical machines with a liquid cooled casing around the stator (often referred to as cooling jacket) are analyzed and a novel approach is presented. The proposed method aims at creating computationally efficient 3D multi-physics models of electrical machines with liquid cooled jacket. This model is based on the assumption of a fully developed flow in the cooling jacket which allows to scale the CFD simulation to 1D. The slot with a two layer concentrated winding and potting material is modeled using a composite material comprising of both the conductors and slot filler. Similarly, a unified material is used to model the end-windings. Experimental results on a traction machine for vehicle applications are presented showing good agreement with the simulations. Also, a comparison with a 3D CFD is presented to verify the pressure drop in the pipe bend. Finally, the model is used to simulate a dynamic load cycle, which would be computationally extremely demanding with combined 3D CFD and thermal FEA of the machine and its cooling.
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For high-speed permanent magnet machines (HSPMMs), the permanent magnet (PM) is more likely to suffer irreversible demagnetization because the heat dissipation is serious in the HSPMMs, especially for the high power machines. This paper focuses on the comprehensive research results on the power loss and thermal characteristic for a high power HSPMM. First, the power loss at rated load is investigated by finite element analysis. Then, the temperature distribution of four cooling schemes are compared by the electromagnetic-thermal iteration calculation. The effect of different parameters on thermal behavior is obtained to reduce rotor temperature, which includes an examination of the axial flow duct, cooling medium, sleeve thickness and sleeve thermal conductivity. Finally, an improved loss separation method is employed to obtain the loss distribution from the measured total loss and the comprehensive experiments are implemented based on one HSPMM prototype (800 kW, 15 000 rpm) to verify the related theoretical analysis.
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In this paper, a novel predicting model of artificial neural network (ANN), which can be used for the PHP with different working fluids and wide operational conditions, was proposed for the first time to the author's knowledge. The Kutateladze number (Ku), Bond number (Bo), Morton number (Mo), Prandtl number (Pr), Jacob number (Ja), number of turns (N), and the ratio of the evaporation section length to the diameter (l e /D)were selected as the input parameters. The characteristic temperature to calculate the dimensionless number was the coolant temperature, rather than the average temperature of the evaporator and condenser, considering the latter one was still unknown in the early design stage. The predicted results agreed with the experimental data very well. The MSE and the correlation coefficient of the ANN model were 0.0138 and 0.9824, respectively. Meanwhile, the evaluation method for the evaporation section and condensation section temperature was also presented with a lumped parameter method. The calculation flow charts for two typical conditions, with the knowing of coolant temperature and knowing the heat source temperature, were also given. This paper was expected to be a good reference for the potential application of PHP.
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The output, efficiency, and durability of in-wheel motors in electric vehicles (EVs) depend on heat dissipation performance; therefore, effective active cooling is essential. However, investigating flows under high-speed conditions and predicting component temperatures that cannot be measured by direct contact requires a reliable numerical analysis model. In this study, the oil spray cooling of an in-wheel motor was compared with an in-wheel motor with only simple channel cooling, and to motors with conventional stagnant and circulating which is adapted conventional motors, and at base speed (4400 RPM) the coil absolute temperature induced by spraying was 25.0%, 11.6%, 15.8% lower than conventional methods, respectively. At base speed (4400 RPM) and maximum speed (11,000 RPM), the average heat transfer coefficients of the direct spray cooling area were 5270 Wm ⁻² K ⁻¹ and 10,849 Wm ⁻² K ⁻¹ , respectively; the heat transfer coefficients of the secondary flow cooling area were 2372 Wm ⁻² K ⁻¹ and 8913 Wm ⁻² K ⁻¹ . The oil film's cooling effect increased with increasing motor speed, and the ratio of the oil film's conduction heat transfer to the oil spray's convection heat transfer was 9.8 times higher at maximum speed that at base speed.
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Permanent magnet synchronous motors (PMSMs) are widely used in pure or hybrid electric vehicles for transportation applications. The cooling strategy for PMSMs is still a challenge in the field of thermal engineering. This study presents a novel thermal management method/design based on phase-change heat pipes for PMSMs. Two thermal management modules (TMMs) with different heat-pipe layouts are prepared, including the straightly embedded module in an enclosure (SEME) and three-dimensional rounding module (RM). The impacts of different ambient temperature and various working condition on the cooling effectiveness of the two modules are analyzed experimentally and numerically. Experimental results show that by replacing the convectional motor stator with this heat-pipe-based enclosure component, the effective time to control the temperature of a PMSM can be prolonged by 28.6 and 21.4% when the motor operates continuously under high-speed and high-torque conditions, respectively. The peak temperature of the PMSM under rated conditions can be significantly reduced by 22.3%, which helps increase the power density of PMSMs. Besides, both experimental and simulation results show that the use of a SEME promotes higher heat dissipation ability than RM.
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A direct cooling design using hollow conductors with the coolant flowing inside can significantly improve the heat dissipation in an electrical machine. To predict the thermal performances of an electrical machine with such cooling configuration, this paper proposes a computationally efficient thermal model of hollow conductors with direct cooling features. The hollow conductor is modelled using four equivalent solid cuboidal elements with a three dimensional thermal network and internal heat generation. The heat transfer coefficient between the coolant and conductors is determined by an empirical model considering fluid dynamics behaviors. Axial discretization is performed to take into account the non-uniform temperature distribution along the axial direction. Experimental validation is performed with a U-shaped hollow conductor test rig. Compared to computational fluid dynamics analysis, the proposed thermal model is much more computationally efficient, and thus can be incorporated into design optimization process and electro-thermal simulations of the electrical machine over a driving cycle.
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Thermal analysis is a key aspect in electrical machine design and in particular for those operating with severe duty where a high-reliability thermal analysis is required. This paper presents a comprehensive analysis of techniques for calibrating generic thermal model of electrical machines. The proposed approach combines two existing experimental methods commonly used in thermal testing of electrical devices. The first method uses a short-duty transient excitation to derive the winding thermal parameters, whereas the second method uses a steady-state excitation to inform thermal parameters related with heat transfer across from the winding body into the machine periphery. Both testing methods are based on a well-defined heat source provided by a dc excitation. In contrast, the existing methods for calibrating thermal models usually combine the winding thermal data predictions and a set of experimentally derived temperatures from dc tests. Such approach however, might be inadequate if not supported by experimental data with a sufficient number of test points. This frequently leads to an under-defined calibration process, with several unknown factors, each of which has a significant impact on the reliability of temperature predictions. The main advantage of proposed approach is the combination of the short-transient and steady-state testes that allows reducing the number of free parameters and it provides a more systematic calibration process. In addition, a detailed test procedure for generic thermal model calibration is presented and discussed.
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