Chengde Tong

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.

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.

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.

Research on the Magnetic Characteristic of a Novel Transverse-Flux PM Linear Machine Used for Free-Piston Energy Converter

Free-piston energy converter, composed of a free-piston engine and a permanent-magnet (PM) linear machine, is a promising generator concept for series hybrid electric vehicles (HEVs). In this paper, a novel transverse-flux PM linear machine is investigated for such applications. Unlike conventional transverse-flux machines, the proposed machine features simple mechanical structure. Flux leakage of the proposed machine is analyzed, and parameters of the machine are optimized by finite-element method (FEM). Compared with conventional flux configurations, such as radial flux, axial flux and Halbach, the proposed transverse-flux topology showed advantages in low cogging force, low thrust fluctuation, and high efficiency. A prototype was designed and manufactured. Further experiments indicated satisfactory load characteristic of the machine.

Electromagnetic Design and Control Strategy of an Axially Magnetized Permanent-Magnet Linear Alternator for Free-Piston Stirling Engines

A 1-kW axially magnetized permanent-magnet linear alternator and the control strategy are investigated for free-piston Stirling engines (FPSEs). To meet the requirement of FPSE applications, the power densities of axially magnetized and radially magnetized structures are compared, and the shape of the stator end tooth is studied to reduce thrust fluctuation. Moreover, the thermal field of the proposed alternator is investigated for the appropriate selection of insulation class. The equivalent method is used to simplify the thermal modeling of slot coils. Due to the complex control of the FPSE, the stroke control strategy is investigated. Energy storage devices are employed to provide transient power supply and reduce voltage ripple. The hardware structure and voltage control scheme are discussed and validated by Matlab/Simulink. The prototype alternator and controller were designed and tested, and satisfactory experimental results were obtained.

Optimization of an 80 kW Radial-Radial Flux Compound-Structure Permanent-Magnet Synchronous Machine Used for HEVs

Compound-structure permanent-magnet synchronous machine (CS-PMSM), which is composed of a stator machine (SM) and a double-rotor machine (DRM), is a new power-split concept for hybrid electric vehicles (HEVs). To compare the CS-PMSM system with Toyota Prius based on the planetary gear unit, an 80 kW radial-radial flux prototype machine is designed. Fractional slots are employed for SM and DRM and the slot openings and pole-arc embraces of the two machines are optimized to decrease torque fluctuation. As the outer rotor is the structural and magnetic common part of SM and DRM, the magnetic circuits of the two machines are coupled. To obtain the thinner outer rotor and to decrease magnetic saturation of the outer rotor during machine design, the influences of the thickness and pole-arc embraces of permanent magnets on magnetic coupling are investigated by finite-element method. The magnetic field in the outer rotor may reach saturation, due to the impact of armature reaction on the flux distribution in the outer rotor. Under the condition of armature reaction, the flux distribution and electromagnetic torque are analyzed.

Topology Comparison of Compound-Structure Permanent-Magnet Synchronous Machines

A compound-structure permanent-magnet synchronous machine (CS-PMSM) system is a hybrid-electric-vehicle power-train concept. Six typical topologies of CS-PMSMs are proposed. The characteristics of different CS-PMSMs are compared and evaluated from the aspects of torque density, manufacturability, heat-dissipating capability, and magnetic coupling. The selecting principle of different topologies is proposed for practical application.