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With the increasing energy shortages and environmental degradation, electric logistics vehicle (ELVs) with energy conservation and environmental protection has become a research hotspot. The design of machine is the key to develop ELVs. Magnetic field analysis is the most critical issue since its accuracy affects the calculation of motor torque, loss, and other characteristics. To provide a calculation method for the field and performance analysis of the machine for ELVs, this paper presents an analytical model of air-gap field for hybrid excitation and interior permanent magnet machine. In the proposed model, it is taken into account for the shape of the stator and rotor teeth. The flux density on the rotor side is derived by equivalent magnetic circuit (EMC) with leakage magnetic flux. Taking the calculated flux density as one of the second boundary conditions, the air-gap field distribution is calculated by magnetic potential model with the eccentricity of the rotor. To verify the analytical method, we adopted the finite element method. The simulation results of the air-gap flux, back electromotive force, and cogging torque are in good agreement with the analytical results. Besides, applying the analytical model, the machine can be optimized for obtaining the optimal air-gap flux density distribution. The hybrid excitation machine with salient pole and interior magnets can provide a good flux density waveform. The study offers a helpful analytical method for design and optimization of the type of machine for ELVs. INDEX TERMS Analytical method, hybrid excitation and interior permanent magnet machine, equivalent magnetic circuit (EMC), the eccentricity of the rotor.

The differential drive two-wheeled inverted pendulum mobile robot has advantage of high maneuverability on slopes and in narrow spaces. It can be used to carry human beings as well as other goods. This paper mainly discusses mechanical design and dynamic modeling of this type of mobile robot platform. The first prototype is 12 kg of weight with dimensions of 42x36x15 cm. A multi modal control system is developed which includes the human transport control system and goods transport control system mode. An embedded control system is implemented to control two motors for both modes. In human transport mode the master controller receives the data from the data conditioning module and generates the reference for PID controllers whereas in goods transport mode the master controller receives command from the teleoperator. The effectiveness of the developed mobile robot is confirmed by experiments such as climbing slope, pivot around and surpassing small obstacles.

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