We have developed a cell concept drive system, namely, an entire drive system is divided into minimum function cells, which enables to create a just-fit drive system by a suitable combination of these cells. Another advantage of this system is that partial renovation of each cell is possible, which is effective for extending product life. However, one important problem with this system is that some cells are used longer than the other cells, which increase their risk of failure.

In this paper, we discuss how to reduce the above risk from the perspectives of self-detection of failure symptoms and preventing the occurrence of failure from spilling over to the entire drive system, by using an example of DC voltage sensor failure. First, we propose a fault diagnosis method with offline self-checking for DC voltage sensors. Then, we discuss a new control method that enables drive systems to work continuously, even when sensor fault occurs, by using a prediction signal with the other sensors, instead of a fault sensor signal. Finally, the effectiveness of the developed methods is demonstrated experimentally with a prototype drive system.

This paper presents a new battery self-traction system for high-speed trains. We developed an SiC applied traction system for the latest Shinkansen train, Series N700S. The developed system is so compact and lightweight that it saves space and weight, which can be used for new equipment under the floor of the car body. Utilizing the released space and weight, we started developing a novel battery system for traction to use in case of power failure of the catenary. This is the first battery self-traction system for high-speed trains in the world. In this paper, we introduce the design philosophy and procedures and discuss the results of the running tests.

In-motion wireless power transfer (WPT) is expected to solve many problems of electric vehicles (EVs). In order to transfer a large amount of energy to vehicles running at high speed, quick-start charging is needed. However, the sudden starting of the power transmission causes a large current overshoot, which damages the equipment of the WPT system. Therefore, it is commonly thought that the transient property of current must be improved. However, a transient control method with an accurate circuit model for EV applications is yet to be developed. Here, we propose a novel control method using the envelope model of the transient response. We applied the precise envelope model with d-q conversion to the starting of the power transmission considering the different modes of diodes. By calculating the inversion of the circuit model, the input voltage trajectory that achieves the desired current trajectory was theoretically obtained. Finally, the proposed method enabled quick-start charging without causing any current overshoot. This method is expected to be an essential technique for the practical use of in-motion WPT.

In this paper, an electric wheelchair with a low-cost force sensing mechanism was developed for power assistance on a steep slope. Steep slopes can be found in mountainous areas and so on. In particular, 17^° slopes have been used in some mobile examination cars, in which, two or three staffs have to push and pull a wheelchair so that it can enter the car and enable medical examinations to be conducted. However, most electric wheelchairs in the market cannot climb such a steep slope. Therefore, in this study, we first developed an electric powered assistive wheelchair for such steep slopes and then proposed extended admittance control to provide assistance when climbing such slopes. The extended admittance control can distribute the burden due to the gravity of the entire wheelchair and the rider to the caregiver and the electric wheelchair. Meanwhile, an automatic parameter adjustment method was proposed for deriving the maximum power of the motor for assistance according to the weight change of the wheelchair and the rider. Verification experiments were used to evaluate the proposed assistive control, and its effect was verified.

The use of triple active bridge (TAB) converters in distributed electric grids has attracted considerable attention because of their multi-directional power connection, insulation performance, and small size. However, there remains a problem with respect to the interaction between two current loops with TABs, and there are few solutions to this problem when an AC supply is connected to the system. In this paper, we propose a method to suppress the interference by using iterative control as the main approach, taking into account the occurrence of periodic disturbance in the TAB converter when connected to an AC system. In order to estimate the characteristics of the proposed method, a prototype is built and tested experimentally. As a result, it is confirmed that the measured grid current THD is within 5% and that he battery current ripple decreased by 84% at a maximum.

A series elastic actuator (SEA) using an ultrasonic motor (USM) and an elastic element has attracted attention as a compact actuator with high torque-weight ratio and high force control performance. However, an elastic element in a SEA often causes mechanical vibrations. To suppress these vibrations, studies implemented the state feedback of the motor- and load-side angles. However, as the controller has many integrators, the control system becomes unstable when the angular-velocity of the USM is saturated. Therefore, in this study, integrators in the controller were reduced in number. Furthermore, a limit error feedback controller was designed to suppress the windup phenomenon caused by the integrators. The frequency analysis using a describing function showed that stability is guaranteed even if the angular-velocity is saturated. In addition, the experimental results indicate that an overshoot of the torque response is suppressed.

This paper focuses on energy saving in traction of rolling stocks and discusses the application of energy-saving driving operation. Increasing the maximum acceleration rate of a rolling stock is proposed using which energy-saving running is achieved by decreasing the powering energy because of the decreasing the rate of powering in the total running time and decreasing maximum speeds. The authors performed on-track tests and obtained 6.0% energy-saving effect by applying the proposed method against conventional running profiles, and 4.8% of that against the previously proposed running profiles without increasing the acceleration rate. The effectiveness of increasing acceleration rate is proven by on-track tests as well as numerical evaluations. Besides, this paper focuses on energy-time plots used for optimization of running profiles that visualize the relationship between energy consumption and running time, and gives a more practical description than optimal running time scheduling. Many on-track tests with various speed profiles were performed during this research. In order to understand the relationships of energy-saving effects of many speed profiles easily in practical use, the authors focus on the difference of the energy-saving effects of the many sections and many test runs, and graphically display relationships between the differences of energy consumption and that of running time. The visual presentation enables a straightforward analysis of the relationship among running time and speed profiles.

Speed sensorless vector control requires accurate motor parameters, but the stator and rotor resistances vary due to the variations in motor temperature. This method requires estimations of the rotor flux and rotor speed. Since the estimations use the machine parameters, the stability of the system is sensitive to the variations of the machine parameters.

In this study, the stability analysis of a speed sensorless vector control system based on speed observer is carried out. The stability of the speed sensorless vector control system of a three-phase squirrel cage induction motor is analyzed. First, a novel differential equation for speed observer is introduced, and the stability analysis method is proposed. Then, the stability effects of the stator resistance, rotor resistance, rotor speed command, load torque, and observer gain are considered.

This paper describes the starting characteristics with or without a starting circuit by comparing the analysis and experimental results. Based on the analysis results, the maximum phase current for the field circuit with the starting current is 17% less than that without the circuit. The time required by the circuit to achieve synchronous speed is 30% faster because of the starting circuit. In the motor without the starting field circuit, increased current and decreased acceleration are observed because of the braking torque. As the starting characteristics are considerably altered by the voltage drop and unbalanced three-phase voltage, these factors were considered in the analysis. From the experimental results, it was confirmed that the phase current and acceleration time agreed with the analysis results.

We have been studying the application of amorphous metal with low loss to axial gap motors. However, since radial gap motors are the most widly used motors, a motor structure that can apply amorphous metal to a radial gap motor was studied. In our previous study, we reported the study on SPM motors with concentrated winding. In this study, we evaluated the effect of high efficiency on the distributed winding IPM motor with high magnetic flux density inside the iron core. As a result, it was confirmed that the efficiency can be improved by reducing the iron core loss.

Photovoltaic (PV) and battery (BT) power conditioning systems (PCSs) exhibit the potential to cope with the energy issues we will face in the future. This study establishes an energy system with PVs and BTs that will correspond to `upward and downward Demand Response' by using the receiving power variable control of PCS. According to the measured receiving power, energy management system (EMS) control is enabled by using the receiving power variable control of PCS without using the exclusive controller. The effectiveness of this system is verified using a simulation and actual equipment.