Train conductors must issue a departure signal to drivers after verifying platform safety before the trains can depart the stations. The judgments on departure signals differ for different conductors based on the differences in platform conditions. An experiment was conducted with 18 experienced and 18 young conductors to examine the factors affecting conductors' judgments. The results indicated that conductors' judgments were strongly affected by passengers' positions and postures and less by the direction the passengers were facing. Most importantly, 9 experienced and 1 young conductor tended to give the departure signals when passengers were standing or half-standing between the platform braille blocks and trains. Developing new measures to prevent departure signals when passengers are standing between the platform braille blocks and trains is expected to prevent platform accidents involving humans.

In this study, an asymmetric rotor was developed to reduce the cogging torque and torque ripple regardless of the rotational direction and its driving point. Specifically, the rotor had a linear symmetric structure for bi-rotation. In addition, a π-shaped pole rotor was proposed as a new structure to alleviate magnetic saturation at the edge parts of the rotor. Optimal design using the Rosenblock method revealed that the proposed structure can reduce the cogging torque and the torque ripple in a wide range of driving conditions.

Lithium-ion batteries in electric vehicles must be adequately heated at low temperatures to prevent the decrease in discharge capacity. Therefore, ac heating techniques that use the Joule heat generated by the internal resistance of batteries have been proposed. Although these techniques achieve higher heating efficiency and uniform heating, they require an ac heating inverter to produce ac current, resulting in increased system complexity and cost. In this study, a dual active bridge converter that integrates an inverter for ac heating in electric vehicles is proposed. The proposed converter is derived by sharing two legs of both converters, thus achieving a simplified system and low cost. This converter operates either in the ac heating or power transfer mode. These modes operate at different switching frequencies and are independent of each other. Experimental results of a prototype for a 12-cell battery demonstrated that in addition to the bidirectional power flow, the proposed converter can heat up the 12-cell battery from -11°C to 0°C within 10min.

This study proposes a modular multilevel converter by applying a balancing circuit with a resistor for a low-voltage grid converter. The proposed balancing circuit, which is controlled by the same gate signal as that of the main switch, can reduce the loss of the additional balancing circuit and the current rating of the balance switch without the need for additional the cell capacitors. Only one voltage sensor per converter arm is required to automatically balance the cell capacitor voltages. The experimental results indicate that the cell capacitor voltages are well balanced during a rated operation of 10kW and a high efficiency of up to 99.2% is achieved, which is almost the same as that without a balancing circuit.

In recent years, the demand for miniaturized electric motors with high output power density has significantly increased. High power density can be achieved by increasing the rotation speed thus, research on ultra-high-speed motors is being actively conducted. Ultra-high-speed motors have a high operating frequency and large losses inside the motors therefore, it is difficult to cool the rotor for continuous operation. If a concentrated winding structure is used to enhance the output power density, the rotor loss further increases. Therefore, in this study, we focused on the material of the rotor retaining sleeve and designed an ultra-high-speed motor considering the loss density. We developed a prototype machine with separate magnetic bearings from the motors and clarified the precise operating characteristics of the ultra-high-speed motor through experiments. We also report some detailed operating characteristic of the motor under different load conditions.

This paper proposes a technique for applying LC resonance to a rectifier circuit of a self-excited wound-field rotor, which utilizes space harmonics for improving the variable flux function. The rotor magnetomotive force can be improved by setting the resonance frequency of the LC resonance circuit to a low speed rotation range. The adjustable speed drive characteristics and efficiency maps are demonstrated via a prototype.

Hydrogen generation systems using powdery sodium borohydride (NaBH₄) have been attracting attention owing to their higher energy density and lower infrastructure costs than current mainstream high-pressure hydrogen tank systems. In order for a NaBH₄ hydrogen generation system to produce the desired amount of hydrogen, the concentration of the fuel solution must be properly controlled. However, it is difficult to directly measure the mass of water and NaBH₄, the values of which are needed to derive the fuel concentration. This paper proposes a fuel concentration estimation method using a state observer from measurable parameters such as hydrogen pressure and discharged hydrogen flow rate. In this paper, it is shown that a NaBH₄ hydrogen generation system with an output delay can be represented with a state-space model. A state observer for estimating the concentration of the aqueous solution is designed based on the state-space model. In order to verify the effectiveness of the proposed estimation method, experiments are conducted to estimate the fuel concentration when the fuel input rate is changed and when the fuel concentration is changed during the process of hydrogen generation. As a result, the maximum relative error of the concentration is less than 8.70%, and the validity of the estimation method is clarified when the fuel input rate and the fuel concentration are changed.

This paper proposes the starting method for position sensorless controlled interior permanent magnet synchronous motors (IPMSMs) by using all-pass filters. The starting of IPMSM position sensorless control is well known to be extremely difficult due to the lack of electromotive information. Therefore, IPMSM is often started and accelerated with the high-frequency signal injection in general, and then the control algorithm is switched to position sensorless control without high-frequency injection in middle speed region. However, the acoustic noise due to high-frequency signal injection would occur, and the switching of control methods would cause some bumps. For this reason, IPMSM is desirable to be driven from the start to the steady state without high-frequency signal injection.

This paper realizes to start the position sensorless controlled IPMSM without high-frequency signal injection by all-pass filter with the assistance of the appropriate initial vector setting of each controller, under the assumption that the high-frequency signal injection is used only at standstill. Finally, this paper experimentally demonstrates the feasibility and the effectiveness of the proposed method.

This paper proposes a new voltage command nonlinear modulation method for three-phase synchronous motor drives. This method has the following features: (a) It is simple and can be applied to large initial voltage commands. (b) The modulated voltage command can be seamlessly converged to a six step drive pulse. Moreover the convergence speed can be easily adjusted.

Our research focuses on the power electronics and its practical applications such as electric vehicle (EV), high-efficient battery, and so on. In this report, we give some examples of our study and related activities with showing the real experimental equipment.