Thermal Modeling of Permanent Magnet Synchronous Motors for Electric Vehicle Application

Permanent magnet synchronous motor (PMSM) is a better choice as a traction motor since it has high power density and high torque capability within compact structure. However, accommodating such high power within compact space is a great challenge, as it is responsible for significant rise of heat in PMSM. As a result, there is considerable increase in operating temperature which in turn negatively affects the electromagnetic performance of the motor. Further, if the temperature rise exceeds the permissible limit, it can cause demagnetization of magnets, damage of insulation, bearing faults, etc. which in turn affect the overall lifecycle of the motor. Therefore, thermal issues need to be dealt with carefully during the design phase of PMSM. Hence, the main focus of this thesis is to develop efficient ways for thermal modeling to address thermal issues properly. Firstly, a universal lumped parameter thermal network (LPTN) is proposed which can be used for all types of PMSMs regardless of any winding configuration and any position of magnets in the rotor. Further, a computationally efficient finite element analysis (FEA) thermal model is proposed with a novel hybrid technique utilizing LPTN strategy for addressing the air gap convection in an efficient way. Both proposed LPTN and FEA thermal models are simplified ways to predict motor temperature with a comparatively less calculation process. Finally, the proposed thermal models have been experimentally validated for the newly designed interior and surface mounted PMSM prototypes. Again, a procedure for effective cooling design process of PMSM has been suggested by developing an algorithm for cooling design optimization of the motor. Further, a computational fluid dynamics (CFD) model with a proposed two-way electro-thermal co-analysis strategy has been developed to predict both thermal and electromagnetic performance of PMSM more accurately considering the active cooling system. The developed step algorithm and CFD modeling approach will pave the way for future work on cooling design optimization of the newly designed interior and surface mounted PMSM prototypes

Thermal management of the permanent magnets in a totally enclosed axial flux permanent magnet synchronous machine

Elevated magnet temperature in Axial Flux Permanent Magnet Synchronous Machines (AF PMSM) adversely affects torque production, material cost, and the risk of demagnetisation. These machines show promise in applications requiring high power density, however the factors which affect magnet temperature have rarely been investigated. This is therefore the focus of the thesis. A multiphysics numerical model was formulated which predicted the loss, flow, and temperature fields within an AF PMSM. A criterion for estimating the relative importance of the fluctuating component of a periodic heat source on the temperature response of a device was proposed and validated. In this work it was used to justify a steady state, rather than transient, thermal analysis. Thermometric and electrical measurements were taken from an instrumented AF PMSM to validate the numerical predictions. A novel magnet loss measurement technique was implemented; losses were determined by measuring the initial temperature rise rate of the magnets. This was achieved via a calibration relating temperature rise to voltage constant. It was found that 99% of the heat generated in the magnets was convected to the inner cavity of the machine, due to the inner cavity’s recirculating flow structure this heat was dissipated to the casing and core. As a proportion of all heat entering the inner cavity 56-62% left to the casing while 28-41% left to the core. Magnet hot spots were found to be up to 13% greater than the mean temperature rise. Their location was influenced by the distribution of losses and the direction of shaft rotation. Temperature gradients within the inner cavity caused the magnet’s trailing edge to incur a 10% greater temperature rise than the leading edge. As increasing temperature decreases the coercivity of magnet materials these findings are a crucial contribution to the understanding of devices where local demagnetisation is of concern.Open Acces

Combined multi-physics model of switched flux PM machines under fault operations

In this paper, the transient thermal response of a conventional double layer switched flux permanent magnet machine is studied for both healthy and fault conditions such as inter-turn short-circuit. A highly optimized and accurate co-simulation model for different operating conditions is developed requiring low computation and time resources. The electro-mechanical models for both healthy and faulty operation are implemented in Matlab/Simulink while the thermal model is implemented using 3D FEM software. Both models are dynamically coupled to enable the influence of temperature rise on the electromagnetic performance and vice versa to be predicted. Operation under various conditions are investigated and it is found that the temperature rise under fault conditions and high speed can lead to irreversible demagnetization of the permanent magnets. The superposition principle is used to accurately estimate the impact of short-circuit currents on the temperature rise. A series of dynamic tests are carried out to validate the transient thermal response prediction when operating during both the healthy and fault conditions

Investigation on Multi-Physics Modelling of Fault Tolerant Stator Mounted Permanent Magnet Machines

This thesis investigates the stator mounted permanent magnet machines from the point of view of fault tolerant capability. The topologies studied are switched flux (and its derivatives C-Core, E-Core and modular), doubly salient and flux reversal permanent magnet machines. The study focuses on fault mode operation of these machines looking at severe conditions like short-circuit and irreversible demagnetization. The temperature dependence of the permanent magnet properties is taken into account. A complex multi-physics model is developed in order to assess the thermal state evolution of the switched flux machine during both healthy and faulty operation modes. This model couples the electro-mechanical domain with the thermal one, thus being able to consider a large range of operating conditions. It also solves issues such as large computational time and resources while still maintaining the accuracy. Experimental results are also provided for each chapter. A hierarchy in terms of fault tolerant capability is established. A good compromise can be reached between performance and fault tolerant capability. The mechanism of the magnet irreversible demagnetization process is explained based on magnetic circuit configuration. It is also found that the studied topology are extremely resilient against the demagnetizing influence of the short-circuit current and the magnet demagnetization is almost only affected by temperature

Research on the speed‐dependence of heat convection in high‐speed EV motors and its application in the model‐based rotor temperature monitoring technology

Using the embedded onboard digital thermal model is an economical and effective way to monitor the rotor temperatures of the electric vehicle (EV) propulsion Permanent Magnet Synchronous Motor (PMSM) in real-time. The onboard thermal model is generally in an analytical form with constant thermal resistances. However, in practical situations, the thermal convection intensities on the surfaces of the air gap and the end-cavity vary significantly with the rotational speed, producing a non-negligible influence on the estimation accuracy of the onboard thermal model. Aiming at eliminating this error and improving the accuracy, this paper explores the variation of the airflow's aerodynamics characteristics and the heat convection with the rotational speed through a syncretic study of theoretical, experimental, and numerical methods. It is found that the changing trend of the airflow presents a multi-stage characteristic in the speed range of 0–12, 000 rpm. The speed-dependent convective thermal resistances are formulaically parameterised and then used to replace the related constant thermal resistances in the thermal model. The standard vehicle driving cycle test result shows that this optimisation brings a nearly 11% reduction of the overall estimation error

Analytical thermal model for fast stator winding temperature prediction

This paper introduces an innovative thermal modelling technique which accurately predicts the winding temperature of electrical machines, both at transient and steady state conditions, for applications where the stator Joule losses are the dominant heat source. The model is an advanced variation of the classical Lumped Parameter Thermal Network approach, with the expected degree of accuracy but at a much lower computational cost. A 7-node Thermal Network is first implemented and an empirical procedure to fine-tuning the critical parameters is proposed. The derivation of the low computational cost model from the Thermal Network is thoroughly explained. A simplification of the 7-node Thermal Network with an equivalent 3-node Thermal Network is then implemented, and the same procedure is applied to the new network for deriving an even faster low computational cost model. The proposed model is then validated against experimental results carried on a Permanent Magnet Synchronous Machine which is part of an electro-mechanical actuator designed for an aerospace application. A comparison between the performance of the classical Lumped Parameter Thermal Network and the proposed model is carried out, both in terms of accuracy of the stator temperature prediction and of the computational time required

Structural Optimization and Thermal Modeling of Flux Switching Machine

The point of this study was to model a lumped parameter thermal network for flux switching machine. The model could be utilized to outline new cooling systems and as a developer for this sort of machines. The model developed is a thermal framework having segments essentially focused around existing literature. The losses in various machine sections were thought to have already found from the electromagnetic model. The elemental model can then be utilized to carry out simulations regarding cyclic loading as well as transient activities. The thermal model examined here is partitioned into different sectors, thereby empowering analysis of this machine. The model under investigation has been acknowledged by utilizing a COMSOL Multi-physics simulator and Matlab ® programming software. The heat exchange coefficients are characterized from information gathered from the comparative kind of machines. The developed framework also considers sensitivity analysis in terms of parametric effects on the behavior of the machine thermally. The developed model needs no substantial computing and can simply be run on a personal computer. The model can later be modified and connected to diverse machine developments. Structural topology optimization approach is adopted to find the optimal geometry. As a basic study, two optimization techniques i.e., genetic and simulated annealing algorithms have been adopted with the former based on the process of natural selection and the latter on the process of annealing (heating and cooling of metals). The design goal is to minimize the total dissipated losses to improve the overall efficiency and hence to achieve optimal design results

Structural Optimization and Thermal Modeling of Flux Switching Machine

The point of this study was to model a lumped parameter thermal network for flux switching machine. The model could be utilized to outline new cooling systems and as a developer for this sort of machines. The model developed is a thermal framework having segments essentially focused around existing literature. The losses in various machine sections were thought to have already found from the electromagnetic model. The elemental model can then be utilized to carry out simulations regarding cyclic loading as well as transient activities. The thermal model examined here is partitioned into different sectors, thereby empowering analysis of this machine. The model under investigation has been acknowledged by utilizing a COMSOL Multi-physics simulator and Matlab ® programming software. The heat exchange coefficients are characterized from information gathered from the comparative kind of machines. The developed framework also considers sensitivity analysis in terms of parametric effects on the behavior of the machine thermally. The developed model needs no substantial computing and can simply be run on a personal computer. The model can later be modified and connected to diverse machine developments. Structural topology optimization approach is adopted to find the optimal geometry. As a basic study, two optimization techniques i.e., genetic and simulated annealing algorithms have been adopted with the former based on the process of natural selection and the latter on the process of annealing (heating and cooling of metals). The design goal is to minimize the total dissipated losses to improve the overall efficiency and hence to achieve optimal design results