Ping Zheng

Magnetic Characteristics Investigation of an Axial-Axial Flux Compound-Structure PMSM Used for HEVs

An axial-axial flux compound-structure permanent-magnet synchronous machine (CS-PMSM) system used for hybrid electric vehicles (HEVs) enables the internal combustion engine (ICE) to operate at optimum efficiency region independent of road conditions, thus decreasing the fuel consumption and emissions remarkably. The axial-axial flux CS-PMSM is a high-degree integration of two axial-flux PMSMs. The magnetic coupling problem of the CS-PMSM is investigated based on magnetic circuit and finite-element method (FEM). The influences of the magnet rotor structures on the magnetic coupling are evaluated. Halbach structure is used for the magnet rotor, which makes the design of CS-PMSM more flexible. Further, a prototype machine of the axial-axial flux CS-PMSM was designed and manufactured. The experimental results show that the magnetic coupling problem can be solved perfectly due to special structural design, which verifies the theoretical analysis.

Research on the Cooling System of a 4QT Prototype Machine Used for HEV

A four-quadrant transducer (4QT) is a hybrid electric vehicle (HEV) power train concept. It can enable the internal combustion engine (ICE) to operate at optimum efficiency during all driving conditions with both torque and speed control. The thermal property is a vital problem due to its special configuration. Aiming to find the hot spot and investigate the cooling system of the 4QT, the thermal field is calculated with finite-element method (FEM). The simulation is validated by the comparisons with the experiment. The influences of the forced-air cooling, water cooling, and the distribution of the cooling channels on the cooling performance are discussed, respectively. The stator air ducts are removed, and 12 water channels evenly distributed in the housing are employed. The design principle of the cooling system is presented. The speed impacts of air flow and water flow are discussed and provide a parameter reference for choosing the forced-air cooling fan and water pump properly.

Magnetic Coupling Analysis of Four-Quadrant Transducer Used for Hybrid Electric Vehicles

A four-quadrant transducer (4QT), which is a hybrid electric vehicle power train concept, is a structural integration of two permanent-magnet synchronous machines. It comprises three parts: stator, outer rotor, and inner rotor. As the outer rotor is a structural and magnetic common part of the two radial-flux machines, the magnetic circuits of the two machines are coupled. A new method is put forward to solve the permanent-magnet operating point when considering the magnetic coupling during machine design, and a 4QT prototype machine of 60 kW is designed. The influences of the magnetic coupling on flux distribution and electromagnetic torque are discussed by analytical method and finite-element method, respectively. It can be concluded that the decoupling is easy to perform. The magnetization-direction choice of the two layers of the permanent magnets on the outer rotor is also discussed, and the consistent magnetization is preferred

Investigation of a Novel Five-Phase Modular Permanent-Magnet In-Wheel Motor

To increase the driving comfortableness and reliability of electric vehicles, multi-phase fault-tolerant permanent-magnet synchronous motors (PMSM) are becoming promising candidates, especially for the vehicles adopting in-wheel PMSM schemes. In this paper, a novel five-phase fault-tolerant modular in-wheel PMSM is proposed and investigated. The applicable slot/pole combinations are recommended for five-phase PMSM, and the 40-slot/42-pole scheme is selected for the wheel driven application in this paper. The electromagnetic structure was designed, and the fault-tolerant tooth was optimized to obtain better torque curve. The fault-tolerant ability was analyzed under some fault conditions, including one phase open-circuited, two adjacent phases open-circuited, two non-adjacent phases open-circuited and one single phase short-circuited. The results indicate that the drive system can survive these fault conditions; through proper current control strategies, different fault-tolerant performances can be obtained. The proposed scheme is proved to have satisfying electromagnetic and fault-tolerant performances.

Investigation of a Novel Radial Magnetic-Field-Modulated Brushless Double-Rotor Machine Used for HEVs

A novel brushless compound-structure permanent-magnet synchronous machine (CS-PMSM) with six different topologies is proposed based on the magnetic field modulation principle. As the key part of the brushless CS-PMSM, the radial magnetic-field-modulated brushless double-rotor machine (MFM-BDRM) is investigated on the speed and torque relations of the first-stator magnetic field, the first-PM rotor and the modulating ring rotor by analytical method. Besides, on the basis of analyses of magnetic field distribution in the inner and outer air gap, the back electromagnetic force and torque performance of the radial MFM-BDRM are further studied by finite-element method (FEM). The results indicate that the low power factor is a major problem of the radial MFM-BDRM. Therefore, the influence of parameters, such as combinations of magnetic block number and PM pole pair number, the span ratio and radial thickness of magnetic blocks, and the length of air gap, on the power factor is analyzed. Additionally, to investigate the distribution law of core loss in the radial MFM-BDRM, amplitudes and frequencies of the magnetic fields in each part of the machine are analyzed. Furthermore, considering the weak mechanical strength of modulating ring rotor employing DW310 laminations, an attempt to use iron instead of DW310 in modulating ring rotor is investigated.

Characteristic Analysis and Verification of the Magnetic-Field-Modulated Brushless Double-Rotor Machine

The magnetic-field-modulated brushless double-rotor machine (MFM-BDRM), composed of the stator, the modulating ring rotor, and the permanent-magnet (PM) rotor, is a new power-split device for hybrid electric vehicles (HEVs). Compared with traditional double-rotor machines (DRMs), the MFM-BDRM shows more complicated electromechanical energy conversion relations, due to its special operating principle-the magnetic field modulation principle. To analyze the speed relation in the MFM-BDRM, a diagrammatized method is proposed. It shows that the speeds of stator magnetic field, modulating ring rotor, and PM rotor present a collinear speed characteristic. On this basis, the torque relations of stator, modulating ring rotor, and PM rotor are investigated from the view of a conservative lossless system. Then, a lever-balanced torque map is proposed to analyze their torque characteristic. It shows that the torques of stator, modulating ring rotor, and PM rotor can be calculated by the lever balance principle. The power flow map is further proposed to analyze the power flow characteristic among three ports. In addition, comparison of the MFM-BDRM and the planetary gear shows that the MFM-BDRM can be totally equivalent to an electrical machine and a planetary gear, making it gain a great advantage particularly when the MFM-BDRM is used in HEVs. The electromagnetic performance of MFM-BDRM is investigated by a finite-element method, which shows that the MFM-BDRM has advantages of fine sinusoidal back electromotive force and low torque fluctuation. Finally, the speed and torque analysis and FE results are verified by experiment.

Research on a Tubular Longitudinal Flux PM Linear Generator Used for Free-Piston Energy Converter

The free-piston energy converter (FPEC) is used for a series hybrid electric vehicle scheme, which may have the advantages of high efficiency, compact structure, and reliable operation. The linear generator is an important part in the FPEC, and a tubular longitudinal flux permanent-magnet (PM) linear generator scheme is investigated in this paper. The electromagnetic and thermal properties of the generator are analyzed with commercial software Flux 2D. The generator is optimized from the aspects of material selection and structure optimization. Rare-earth PM material VACODYM 655HR is selected for the permanent magnets, and low-performance low-loss material M235-35A is chosen for the stator lamination. The pole number and machine size are optimized, and the optimum scheme with efficiency of 0.935 and specific power of 1.49 kW/kg is obtained, which meets the requirements of FPEC application

Research on the Parameters and Performances of a 4QT Prototype Machine Used for HEV

A four-quadrant transducer (4QT) is a hybrid electric vehicle (HEV) power train concept. In this paper, a 4QT prototype machine, which is integrated radially by two permanent-magnet synchronous machines [one stator machine (SM) and one double-rotor machine (DRM)], is investigated. The inductances of both the SM and the DRM are calculated with a phasor-diagram based 2-D finite-element method (FEM), which can include the effects of eddy current and saturation. The calculated results show that the effect of eddy current can be neglected for both the SM and DRM inductances, and the cross-magnetization influence on the SM inductances can be ignored but is remarkable on the DRM inductances. The magnetic coupling between the SM and the DRM is calculated with 2-D FEM, and it is found that little magnetic coupling exists, so the SM and the DRM can be controlled independently, which is a very good feature for HEV applications. With the effect of skewed slots considered, the torque and no-load line-to-line back electromotive force (BEMF) curves of the SM and the DRM are calculated with multislice 2-D time-stepping FEM. The average torques of the SM and the DRM both meet the requirements, and the torque ripples are quite low. The calculated and tested no-load line-to-line BEMF curves of the SM and the DRM are both in good agreements. Both the BEMF curves of the SM and the DRM are somewhat similar to sinusoidal ones, which proves a good design of the magnetic structure

A Brushless Claw-Pole Double-Rotor Machine for Power-Split Hybrid Electric Vehicles

This paper investigates a claw-pole double-rotor machine (DRM) for power-split hybrid electric vehicles (HEVs). Based on the mathematical analysis of the machine, the boundary speed-torque characteristic required by the hybrid electric system is studied. To achieve high power density with acceptable torque ripple for automotive applications, the back electromotive force (EMF) and torque performance of the DRM are investigated with respect to the configurations of permanent-magnet rotor, claw-pole dimensions, and air-gap length. Based on the optimized model, characteristics of the claw-pole DRM, such as flux density, inductance, torque, core losses, and efficiency, are investigated by finite-element method. A downsized prototype machine is manufactured and tested. The experimental EMF, inductance, and torque performance agree well with simulation data. A drive cycle containing various working modes of the DRM is carried out, and the feasibility of using the machine as a power-split device for HEVs is validated.

Experimental Evaluation of a Radial-Radial-Flux Compound-Structure Permanent-Magnet Synchronous Machine Used for HEVs

A compound-structure permanent-magnet synchronous machine (CS-PMSM) system used for hybrid electric vehicles (HEVs) enables an internal combustion engine (ICE) to operate within optimum efficiency region independent of road conditions, thus decreasing the emissions and fuel consumption. In this paper a radial-radial-flux CS-PMSM is investigated. It integrates of two synchronous machines radially, one is called Double-Rotor Machine (DRM) and the other is called Stator Machine (SM). A downsized prototype machine of the CS-PMSM was designed and manufactured, and the tests were performed. The back electromotive force (BEMF) and efficiency of the DRM and SM are measured and analyzed, respectively. The BEMFs of both machines are similar to sinusoidal ones, which shows a good design of the magnetic structure, and both machines have efficiencies above 90% in a wide range. The temperatures of the DRM and SM are further measured, showing a good thermal behavior of the stator but serious overheat of the inner-rotor windings, which must be improved.