Xinggang Fan

Thermal Model of Totally Enclosed Water-Cooled Permanent-Magnet Synchronous Machines for Electric Vehicle Application

Totally enclosed water-cooled permanent magnet machines have been widely applied in electric vehicles due to their advantages of high torque density, high power factor, and strong overloading capacity. However, this type of machine often suffers from extremely high ambient temperature in a very limited space, which may lead to serious faults during operation, such as demagnetization. In order to study the thermal performance in depth, after investigation on the air convection within end-space, this paper presents a thermal model which takes into account the influence of the air temperature within the end-space on the temperature distribution by convection. Combining electromagnetic finite-element analysis with thermal resistance network, the thermal model is established, which is based on the law of heat flux balance in two continuous iterative calculations. Furthermore, computational fluid dynamic technology and experiments are implemented to further validate the proposed thermal model.

Study of Direct-Drive Permanent-Magnet Synchronous Generators With Solid Rotor Back Iron and Different Windings

Direct-drive permanent magnet (PM) synchronous generators (DDPMSGs) are gaining more and more attention and application for wind power. This paper presents a comprehensive performance comparison of an external rotor surface-mounted PM synchronous generator equipped with three commonly used winding types, i.e., integral-slot distributed winding (ISDW), fractional-slot concentrated winding (FSCW), and fractional-slot distributed winding. The tradeoff between torque and the power factor, loss distribution, current, torque, and PM demagnetization characteristics under a short-circuit fault and the steady temperature rise are investigated and compared using finite-element analyses. It is found that, generally, FSCW PM generators exhibit high rotor losses compared with ISDWs, which will lead to an overly high temperature rise. Measures such as segment PMs and the adoption of lamination steel in the rotor can reduce the rotor loss and greatly improve the machine efficiency. However, the temperature rise of FSCW machines is still higher than that of ISDW machines. The conclusion is intended to help choose the proper winding types.

Rotor design for a high-speed high-power permanent-magnet synchronous machine

Permanent-magnet synchronous machines (PMSMs) are considered a very promising machine type for high-speed applications nowadays. As permanent-magnet (PM) materials are generally fragile, a high strength sleeve is required to protect the PMs from damage due to extreme centrifugal forces. The rotor sleeve occupies space of the effective air gap of the PMSMs, so it is difficult to perform the electromagnetic (EM) design without an accurate estimation of the sleeve thickness, which is determined by mechanical issues. In this paper, an integrated mechanical-electromagnetic design method is presented for the rotor of a high-speed PMSM designed for 200 kW at 40,000 rpm. Three commonly used sleeve materials are investigated and their mechanical performances are analyzed. The mechanical strength limits for the proposed machine are calculated, as well as the EM design limits. The optimal dimensions for the rotors with different sleeves are then obtained by combining their strength and EM limits. The EM, thermal and rotor dynamic performances of the designed rotors are analyzed in order to select the best rotor type. In the end, a new rotor topology is proposed to reduce the rotor eddy current losses. The new rotor topology is characterized by a multi-layer sleeve which is thinner than a single-layer sleeve. The rotor losses are significantly lower in the new rotor and easier to be cooled.

Split ratio optimization of high-speed permanent magnet synchronous machines based on thermal resistance network

The split ratio is a significant parameter which affects the torque output and efficiency of permanent magnet machines. It has been optimized for obtaining the maximum torque output with a fixed maximum allowable copper loss or current density as the thermal constraints in the current findings. However, these indirect thermal constraints could be influenced by the split ratio due to the changing machine dimensions and may fail to limit the winding temperature rise. To solve this matter, an analytical split ratio optimization method is proposed in this paper based on the thermal resistance network (TRN). It takes the winding temperature rise limitation as the thermal constraint directly. Both the influence of the core loss and air-friction loss on the optimal split ratio is considered in the analytical optimization method. The proposed analytical method is validated by the electromagnetic and thermal finite element analysis (FEA).

Ventilation and thermal improvement of radial forced air-cooled FSCW permanent magnet synchronous wind generator

Computational fluid dynamics (CFD) method is implemented to investigate the flow and heat transfer within the radial forced air-cooled fractional-slot concentrated-winding (FSCW) permanent magnet generator for decreasing ventilation loss and temperature rise. Firstly, a CFD model is established and the losses and boundary conditions are determined. Secondly, the fluid and temperature field of machines with different channel numbers and channel widths are calculated, and the ventilation and thermal performance are compared. Finally, an alternative cooling structure with radial winding holes through the slot center to dissipate heat from the winding directly, especially for the FSCW permanent magnet generators, is proposed in this paper. The results show that it is a promising alternate for decreasing the winding temperature.

Design of a linear vernier permanent magnet machine with high thrust force density and low thrust force ripple

This paper introduces a novel linear vernier permanent magnet machine (H-LVPMM) with high force density and low force ripple. The permanent magnets (PMs) on secondary uses Halbach array, which can provide a larger flux density in the air gap than that of the conventional surface-mounted PMs configurations, and the primary is composed of three modules, which are separated by two flux barriers. Moreover, the three-phase winding connections and the length of the two flux barriers are specially designed to minimize the cogging force and the ripple force. In order to show the superiority of the H-LVPMM, a conventional linear vernier permanent magnet machine using surface-mounted PMs (S-LVPMM) is built and compared to the proposed machine in terms of back electromotive force (back-EMF), cogging force, average thrust force, thrust force ripple, etc.

Comparative thermal analysis of IPMSMs with integral-slot distributed-winding (ISDW) and fractional-slot concentrated-winding (FSCW) for electric vehicle application

Fractional-slot concentrated-winding (FSCW) interior permanent magnet synchronous motors (IPMSMs) have been attracting considerable attention due to their high power density, high efficiency, short end-winding, high slot fill factor, low cogging torque, excellent flux-weakening and fault tolerance capability. However, compared to integer-slot distributed-winding (ISDW) IPMSMs, the key challenge of using FSCW configurations is the significant rotor losses, particularly at high speed. To figure out the IPMSM with which winding configuration is more suitable for electric vehicle (EV) application, the thermal behaviors of four IPMSMs with ISDW, single-, double- and four-layer FSCWs are comprehensively and comparatively investigated in this paper. Firstly, electromagnetic design and loss analysis of the four IPMSMs are investigated to meet the EV traction motor requirements. Secondly, finite element method (FEM) is employed to investigate the thermal performance of the IPMSMs under different rotational speeds and torque overload capacities. Besides, the influence of magnet segmentation on the temperature is also taken into account. Finally, some conclusions are drawn for the suitable winding configuration selection and the PM traction motor design.

Rotor loss calculation and thermal analysis of a dual-stator axial-flux permanent magnet machine with combined rectangle-shaped magnets

This paper presents thermal analysis of a water-cooled dual-stator axial-flux permanent magnet (AFPM) machine with focus on the sandwiched rotor. The rotor of the machine is featured by combined rectangle-shaped magnets. Firstly, the eddy current losses in the PM are calculated and analyzed. Secondly, lumped-parameter and FE thermal models are established to calculate the temperature distribution of the machine. The results of the two methods show good agreement. Additionally, a detailed thermal analysis of the rotor is carried out. It shows that the segmented PMs can be efficient to reduce the eddy current loss and the non-uniform eddy current loss density of PM has a significant influence on the location of the rotor hot spot.

Effect of AC losses on temperature rise distribution in concentrated windings of permanent magnet synchronous machines with parallel strands

This paper investigates the effect of AC losses on the steady-state temperature rise distribution in concentrated windings of permanent magnet machines with parallel strands by combined electromagnetic and thermal finite-element analyses. The copper losses are decomposed into DC loss, strand-level AC loss and bundle-level AC loss. It shows that the AC losses can significantly increase the winding temperature and influence the temperature distribution in the slot. The bundle-level loss becomes dominant at high speed but has a small influence on the location of the hot spot in the slot, while the strand-level loss could pull the hot spot to the slot opening. A 12-slot 10-pole FSCW permanent magnet machine was prototyped and measured to validate the effect of AC losses on the winding temperature rise. The obtained results could be helpful for designers to build a detailed lumped-parameter thermal model of the winding or for the manufactures where to insert a thermal sensor to capture the real hot spot in the slot.

Cogging torque minimization of SMC motor with axially tapered stator tooth tip

In this paper, a novel stator structure with axially tapered stator tooth tip is proposed to mitigate cogging torque and reduce the machine back EMF harmonics. Furthermore, the stator tooth tips are specifically designed to provide balanced axial electromagnetic force. In order to realize continuous variation of stator tooth tip widths, the soft magnetic composite (SMC) material is used for the stator core. It is theoretically demonstrated that the cogging torque of the new structure can be reduced greatly compared with the conventional stator structure. Finally, the theoretical analysis results are confirmed by the finite-element analysis (FEA) results. A prototype has been designed and under manufactured.