We are developing a small and lightweight direct-drive system toward realization in-wheel electric vehicles (EVs). To increase the power density of the motor, we developed a direct-cooling motor that immersed core, coils, and magnets in cooling oil and improved cooling efficiency. Moreover, we performed measurements of frictional loss, measurement of pressure drop, and continuous heat-run test on the test bench. The results demonstrated that direct cooling is effective and continuous operation can be achieved. Additionally, it was found that the coil temperature can be controlled by the flow rate of the cooling oil. In this paper, we report the concept of direct cooling and the measurement results.

Permanent magnet synchronous motors (PMSMs) are employed in numerous applications as high-power-density and highly efficient drive sources. Notably, multipole PMSMs are key in achieving high output densities for PMSMs. However, multipole PMSMs decrease the sensor resolution and increase the error. In this study, we developed a control technology to reduce the position detection error of a resolver with a specific frequency for a PMSM drive system with a position sensor and verified its effect with HILS and through an experiment.

Flux-based cascade vector control is proposed, which uses flux instead of current for torque control. The proposed method does not require any step-response test but instead employs a steady-state test for torque-response calibration. The method is verified by conducting an experiment using an EV motor. A reduction in calibration time is realized with precise torque control response.

The limit levels of radiated EMI for IH cookers were revised to lower values in December 2018 by the Electrical Appliances and Materials Safety Act. In this study, a switching noise mechanism and its countermeasures for an IGBT loaded into a voltage resonance circuit of an IH cooker is analyzed. A device model is developed using a BSIM3 MOSFET model with voltage-dependent capacitors. The inductor and capacitor load switching operation, including the parasitic elements of a test circuit, is simulated, and switching noise generated during turn-off transient conditions is discussed. An effective method for EMI suppression is proposed based on optimization of the C-voltage characteristics and the addition of an external capacitor. The effect of reduced radiated EMI levels is discussed.

This study develops a magnetic-geared motor with a controllable maximum transmission torque. The maximum transmission torque decreases because the amount of permanent magnets is decreased to enhance the assemblability. However, the DC currents double the maximum transmission torque and this is dozens of times higher than that of a conventional magnetic-geared motor. The operational principle that controls the maximum transmission torque using DC currents is established. Finally, the inherent characteristics of the developed magnetic-geared motor are obtained. In particular, a torque more than the maximum transmission torque can be output under load and the maximum torque is obtained when the phase angle difference between rotors is around 30 to 40 deg.

In DC-electrified railway systems, light-load regenerative brake control prevents the occurrence of overvoltage at the filter capacitor (FC) of the traction inverter of the regenerative vehicle. However, such control can restrict regenerative power more than necessary when the distance between the powering train and regenerative train is increased, although a sufficient load exists in the electric traction system. This study clarifies the principle of the method to restrict torque current of the regenerative train based on the load power. Subsequently, a method is proposed to design the load power estimation controller.

In this study, a direct drive in-wheel system is proposed as a high power density system for reducing the intermediate parts, such as a speed reducer by increasing the torque. We propose a design strategy to show that multipolarization and the improvement of the gap magnetic flux density can effectively increase the power density. A Halbach array magnet rotor that combines the main electrode magnets and spoke magnets with the core is adopted as a technique for improving the gap magnetic flux density. We compare the Halbach array type rotor to the conventional SPM type rotor by using both of magnetic circuit calculation and FEM analysis. Moreover, the actual sized in-wheel motor prototype with the developed Halbach array magnet rotor is fabricated and measures the no-load induced back EMF. The measured no-load induced back EMF agrees well with the analyzed waveform.

When railway operators devise a rolling stock schedule plan, it is desirable that the schedule plan for the new timetable is similar to the previous schedule. In this study, we focus on rolling stock scheduling following a large-scale natural disaster. Generally, partial suspensions occur some sections in the line from the damage caused by the disaster, so a temporary timetable is generated. Subsequently, a rolling stock schedule that is close to the previous one must be created. We propose a two-phase rolling stock scheduling algorithm for the temporarily changed timetable. The proposed scheduling algorithm creates a set of duties based on the multi-commodity network flow problem in the first phase. Following that, the algorithm provides a set of rosters by solving the travelling salesman problem. Finally, we confirm that the proposed algorithm can produce a good solution in terms of evaluation criteria and computational time.

Hybrid railway vehicles have been introduced to save energy in non-electrified lines. However, their high degree of freedom makes it difficult to establish theories that will allow the development of optimal charge and discharge control methods. Nevertheless, it is possible to achieve optimal charge and discharge control by using reinforcement learning. Therefore, in this paper, reinforcement learning models are proposed for charge and discharge control in hybrid railway vehicles.

Peak current-mode control is a control algorithm for switched-mode power supplies (SMPSs) that is characterized by high-speed response and high-stability. Currently, a method of implementing peak current-mode control in a digital controller has been proposed however, there is a limit to increasing the switching frequency. Therefore, in a previous study, we proposed a method that enables high-frequency switching by applying a control method called multi-cycle control, which applies the same ON duty ratio over multiple switching cycles to the existing method. Furthermore, in peak current-mode control, an unstable phenomenon called subharmonic oscillation occurs, which is problematic. Generally, this problem is solved by slope compensation however, it cannot be applied to multi-cycle control. Therefore, in previous work, we derived the condition to suppress subharmonic oscillation by designing parameters of multi-cycle control. In this study, we verified the above-mentioned conditions using a real-circuit.

This paper proposes a control method of switched reluctance motors without requiring position sensors. A pulse voltage is applied to the unexcited two windings and their currents are observed. By detecting the intersection between one of the currents and the other one multiplied by a certain factor obtains a signal indicating that the rotor is at a certain position. A Phase-Locked Loop block receives this signal and provides the estimated rotor position information. The switching of the winding excitation is controlled using the estimated information. Experimental results confirm that the estimated position information has almost been the same as the actual rotor angle. Moreover, load and transient tests in speed were performed and their results are presented.