Recently, there has been a gradual increase in the use of battery powered electric multiple unit trains (EMUs), replacing the conventional diesel trains for non-electrified lines of approximately 10-30km. Battery powered EMUs are typically equipped with closed-type traction battery boxes, in which cooling fans are mounted. To improve the performance of battery cooling, we developed a control method for the cooling fans. Our novel method is derived from a thermal network model of the battery box, and is based on the temperature difference between the battery modules and outside air. We conducted an evaluation test for the Series BEC819, an AC-fed and battery-powered hybrid EMU of JR Kyushu. The test results demonstrated that the developed control method reduced maximum temperature of the battery by 1-2 °C in comparison with the conventional constant speed control.

This paper describes an operating method for a PWM rectifier suitable for air-cooled heat pump chillers. The efficiency of chillers have to be improved in the light to middle load ranges, and the harmonic suppression should be reduced in heavy load ranges. To satisfy this requirement, sinusoidal modulation is adopted in the PWM rectifier, by applying over-modulation and two-step boost voltage control. Although over-modulation can reduce switching loss, current distortion remains. In this study, the input current distortion characteristic is derived in the over-modulation, and it is clearly shown that the distortion has a local minimum around a voltage boost ratio of 1.0. Using this characteristic, the efficiency is improved by the operating voltage boost ratio of 1.0 from light to mid-range load. At heavy loads, harmonic restraint and compressor motor high speed rotation are made compatible by boosting the DC bus voltage to the second level. It is confirmed that ac to dc power conversion efficiency is equivalent at the voltage boost ratio of 1.0, and the input current harmonic is reduced by 40% at the boost ratio of 1.14, compared with the test results of two-phase modulation.

This paper discusses the relationship between resonant frequency and load voltage in wireless power transfer (WPT) systems using series and parallel resonant capacitors and proposes a method to express the resonant frequency using an attenuation coefficient. The resonant frequency and load voltage are derived theoretically by using a simple equivalent circuit when the quality factor of the resonant circuit is low. The resonant frequency expressed by the attenuation coefficient can be used to indicate points of similarity of the resonant frequency in each WPT system. Experimental resonant frequencies agree well with their theoretical values and demonstrate voltage-source and current-source operation at the load side.

This study proposes an exoskeleton haptic device using a powder brake and a constant torque spring. The powder brake can change the torque resistance in real time, and the constant torque spring can generate a constant torque. This device is of a wearable type, and is worn on the operator's hand. By combining the powder brake and the constant torque spring, it is possible to generate an arbitrary passive force on the fingertip. Because this device generates passive force alone, it has an advantage from the viewpoint of safety. The proposed device is applied to the master system to control the slave system in a virtual reality (VR) device. Consequently, the operator can perceive the contact force between the VR device and the VR object. VR object exists in VR space, and can provide the contact force with arbitrary plasticity and elasticity. The experimental results confirm the validity of the proposed system.

Conventional contact force control systems using multi-rotor unmanned aerial vehicles without rotor angular encoders are not robust against modeling errors or disturbances around rotor axes. Therefore, this paper proposes a rotor controller that utilizes a rotor angular velocity. Although existing rotor controllers do not feedback a rotor angular velocity, the proposed rotor controller includes a disturbance observer, closed-loop rotor angular velocity controller, and feedback linearization controller, which utilize a rotor angular velocity. Experimental results show that the proposed controller reduces the steady-state error.

This paper describes the principle of DC flux generation of a transformer in the boost mode of a current-type bi-directional isolated DC-DC converter and the effect of DC flux on circuit operation. Then, the circuit behavior in the case where the DC magnetic flux leading to magnetic saturation is generated is analyzed. Furthermore, this paper proposes a control method for suppressing DC flux in the boost mode of a current-fed bi-directional isolated DC-DC converter. Finally, the validity of theoretical analysis and the effectiveness of the proposed control method are verified through an experiment rated in 2.5kW.

Stability analysis is necessary for designing power conversion systems to ensure proper execution of the designed operations. The impedance method is useful for the analysis and it requires input or output frequency characteristics of converters that are often difficult to derive manually and analytically. This paper proposes an automatic formulation and analysis method, which utilizes a general-purpose simulation algorithm for the frequency analysis of an averaged power converter, based on connection and model information of circuit and control elements. This method is generally applicable even to a converter with nonlinear elements, such as a multiplier as far as the objective system can be linearized at the operating point. As application examples, a buck converter and a grid-forming inverter with power control are analyzed for the frequency characteristics of input or output impedances, which are utilized for stability analysis by the impedance method.

This study proposes a novel current detection technique to reduce the current noise in a PWM inverter with a current sensor in series with low-side switches at high modulation index. In the proposed technique, the modulation of the high-side switch is applied to the voltage reference phase with maximum value and the current detection technique compensates currents in the voltage reference phase with medium and minimum values with the current in the voltage reference phase with maximum value. Experimental results demonstrate that the proposed technique can reduce the noise of q-axis currents.

This paper presents a bidirectional wireless power supply system using a matrix converter. The control method of bidirectional power conversion and the sinusoidal control of three-phase AC current to suppress the conduction loss of the primary matrix converter via secondary voltage control are proposed. In addition, a commutation sequence independent of the sign of the current is applied to the matrix converter. The effectiveness of the proposed control method is experimentally verified using a 2kW prototype system.