Global warming and the risk of depletion of fossil fuels are global concerns. The demand for environmental performance of automobiles is becoming severer year by year. In this regard, automotive manufacturers have designed BEVs, PHVs, HEVs and FCVs to meet CO₂ regulation. This report presents the recent technological trends related to the main components of electrical vehicles.

This investigates the miniaturization and high performance techniques for a vehicle traction motor system. A suitable integration structure of motor and inverter with water cooling is studied. Possible structures are enumerated and benchmarked with size, electrical wiring characteristics, and piping performance as indicators. Two suitable structures are extracted and examined in detail. The size or the most suitable integrated motor-inverter structure was 10% lower than that of the second-most suitable structure. By applying a concentrated winding phase-shift dual three-phase motor that exploits an integrated structure, the efficiency was increased by 5% in the low-torque condition is achieved by driving one group of two three-phase motor.

This paper discusses a magnetization state (MS) manipulation method at high speeds with low vehicle vibration for variable flux permanent magnet synchronous machines (VF-PMSMs). VF-PMSMs can achieve lower driving cycle losses compared to conventional PMSMs by changing the MS in the medium speed and medium torque range. To maximize this advantage for reducing driving cycle losses, the MS manipulation capability in this range, which requires higher voltage to change MS than that required in the low speed range, is critical. However, the capability has not been researched very well. In this paper, a MS manipulating method using a straight line stationary flux linkage trajectory (SLλ^sT) is investigated and evaluated. This method uses a straight line flux linkage trajectory in the stationary frame so that the DC bus voltage utilization is maximized while the flux linkage achieves the desired magnetizing point without demagnetization. This method was experimentally evaluated with EV-scale VF-PMSMs, and it was found to achieve full magnetization at a speed almost two times higher than the base speed. The effect of this method on vehicle vibration was studied via simulation using the experimental result and a simple vehicle model that emulates a vehicle powertrain for traction applications.

An Overmodulation drive for a dual winding motor is proposed in this paper. Our Proposed overmodulation drive counterbalances the high harmonic component in an overmodulation drive by compensating the modulation signal of the one of the windings by the other one in a dual winding motor. As the electrical angles of the modulation signal peak in the two windings are different in a dual winding motor, the high harmonic component in one of the windings can be compensated by the other one in a dual winding motor. With our proposed overmodulation drive, the amplitude of the basic voltage increased by 3.5%. Our proposed overmodulation drive is analyzed and the experiment results are confirmed.

The authors have proposed a cell voltage equalizer with an LC series circuit in a previous work. The proposed circuit, however, has the disadvantage that the equalization time tends to be longer than that of other conventional equalizers. Therefore, the authors have studied some control methods to reduce the equalization time. This paper proposes a novel equalization time reduction method using the magnitude relation of each cell voltage estimated from the equalization current for the proposed equalizer. The proposed method can reduce the equalization time without an additional voltage sensor, so the size of the equalizer is not changed and the cost is not higher than an equalizer using the conventional control method. In addition, the characteristics and the effectiveness of the proposed method were verified by the simulations and the experiments. It was confirmed that the proposed method could reduce the equalization time to about 67.7% of that of the conventional control method by the experiments.

In Japan before and after World War II, procurement of oil was difficult, and an alternative fuel for vehicles was necessary. Therefore, an electric motor and charcoal-fuel steam engine were used for the power plant of the vehicle as substitution of the internal combustion engine. Under such a background in such times, this paper introduce the electricity characteristic of the EA-type electric vehicle “DENSO-GO” released by Nippondenso (existing: DENSO CORPORATION) in those days.

The main specifications of electric characteristic of this vehicle were the motor rating output: 6HP (at 1550rpm), battery capacity: 250AH, battery mass: 800kg. The expression EA-type electric vehicle was able to run 195km on one charge though the vehicle's gross weight at that time was 1990kg. This mileage is equal to electric vehicles produced 40 years later.

We have been focusing on automatic train operation (ATO) as a suitable method to evaluate energy-saving operation effects and to improve speed profiles and scheduling. Our previous studies showed some methods of energy-saving operation using ATO. For example, one is to generate “hidden time”, for energy-saving control. Another is to use such a “hidden time” effectively and to apply energy-saving control such as coasting operation. This paper shows an additional method for energy saving by optimizing running time scheduling. ATO controls a train with accuracy such that the optimized schedule can be implemented to minimize the energy consumption. The speed profiles based on this scheduling were installed on the ATO system, and experiments were carried out on track. The results show that the proposed train control and optimized scheduling can save energy by 17% compared with conventional operation processes. The relationships between energy consumption and running time are explained in detail in this paper.

The performance ability of a track circuit is important for safety and reliability of railway operation. Therefore, maintenance of the track circuit is based on time-based maintenance (TBM). However, TBM has a problem in keeping excessive maintenance because it is a uniform method that does not consider the environment of individual equipment. In this study, we focus on condition-based maintenance, which monitors the state of individual equipment and maintains the equipment after any abnormal diagnosis of the equipment before a fault occurs. We expect to realize rational maintenance. Therefore, we propose that the Mahalanobis Distance can be used as a threshold value to show the appropriate time for maintenance. Furthermore, we show the possibility of decreasing the maintenance cost by approximately 20%.

In the last decade, many projects on offshore wind farms have been planned and conducted to be compliant with government policies, especially in Europe. Some projects adopt HVDC transmission using a long-distance submarine cable from offshore to onshore. However, medium-voltage (MV) collection grids use AC, not DC. Moreover, the MW rating of wind turbines have been increasing over the years. The increase in the MW rating has led to higher currents in the MV collection grid and longer distances between wind turbines. Thus, the MVDC collector grid is expected, and an HV DC/DC converter is required to step up the MVDC to HVDC.

This paper introduces a circuit configuration of a high-voltage DC/DC converter with two-series, three-parallel connected IGBTs (2S3P-IGBT) to convert MVDC to HVDC and the switching test results of 2S3P-IGBTs. Further, this paper discusses a design method of a snubber capacitor for voltage sharing and the zero-voltage switching operation in series-connected IGBTs. A bus-bur construction is also discussed to reduce current mismatch in parallel-connected IGBTs. Experimental results show less than 10% voltage imbalance and current mismatch.

We have been studying the application of amorphous metal with low loss to axial gap motors. However, since radial gap motors are the most widely used motors, a motor structure that can apply amorphous metal to a radial gap motor was studied. We propose a structure that uses only amorphous metal for the teeth of a radial gap type motor. It was found that the losses can be reduced by using amorphous metal for the teeth part. By prototyping a motor for industrial use with the proposed structure, a high efficiency of IE5 class was achieved.

Our laboratory focuses on a variety of electric power systems based on power electronics and super conductivity. Further details are found on our laboratory's Web-site (http://www.ec.okayama-u.ac.jp/~epc/).