This paper describes the fluid friction loss that occurs in the part of the rotor that is soaked in oil coolant. The cooling system of this rotating machine includes both oil and water-cooling for the purpose of the reducing the size and weight. We developed a test motor and measured the fluid friction loss and temperature. As a result, (1) it was confirmed that the water- and oil-cooled motor can reduce 24% of the coil and 18% of the coil-end (top) compared with a water-cooled motor; (2) it was confirmed that the water- and oil-cooled motor can increase the output power by 12% compared with a water-cooled motor; (3) it was confirmed that the calculation accuracy of the frictional loss of the oil seal is good (about 6%) at a rotation speed of 5000min^-1, (4) it was clarified that the fluid friction loss in the part of the rotor that is soaked in oil coolant can be calculated at a precision of 30%; (5) and it was clarified that the losses in the water- and oil-cooled motor including fluid friction loss, are the same as the losses in a water-cooled motor, and that the water- and oil-cooled motor has better cooling performance than a water-cooled motor.

Wireless charging technology for heavy-duty vehicles, such as electric buses, has been actively investigated with a view to accelerate the deployment of an important form of eco-friendly transportation. We have developed a wireless power transfer (WPT) system for the rapid charging of electric buses. Most of the performance targets were achieved: the maximum electric power received was 44kW or more, the maximum misalignment tolerance of the transmit and receive charging pads was +/- 10cm or more, and the radiated emission was reduced in accordance with the limits specified by the Radio Act. This paper presents a design method for low radiated emission, and the evaluation of the WPT system.

This paper presents an efficient manual control parameter tuning for positioning controllers in high-performance industrial mechatronic systems. Owing to the complexity of control theory, manual parameter tuning is generally performed by engineers who are unfamiliar with the theory. For instance, the control stability (i.e., gain margin and phase margin) in a feedback (FB) control system often deteriorates the tuning efficiency (time for tuning) due to the trade-off between stability and control bandwidth. Therefore, it takes a long time to acquire expert tuning skills by the trial and error method, which is based on human intelligence. In this study, we propose an optimization problem-based technique for the calculation of a stable FB control parameter area to give unskilled adjusters a visual area of stable parameters, in order to improve the tuning efficiency. The effectiveness of the proposed approach is verified by conducting experiments with a FB controller for the fast and precise positioning control of a galvano scanner.

Interior permanent magnet synchronous motors (IPMSMs) are widely used because their size can be reduced and their motor efficiency can be improved by utilizing the residual flux of permanent magnets. The reduction of flux leakage from the bridge parts of a rotor is one of the important issues to enhance merit. In this paper, two structures to reduce flux leakage were proposed: 1) lightening of the rotor cores by using a multi-holes structure and 2) applying non-magnetic materials for reinforcing the mechanical strength of the bridge parts. Measurement of a prototype applying the above structures was also performed in a no-load and load condition. The no-load test showed a 3.1% increase in no-load back EMF, and the load test clarified that the motor loss at 8.1Nm and 1000min^-1 was decreased by 1% as an effect of bridge narrowing compared with a conventional motor.

In Germany, self-consumption systems with lithium ion batteries (LIB) are required to comply with the laws related to LIB and grid connection. Especially, the safety of LIB is very important for keeping the environment safe if some critical accident occurs. According to the results of a risk assessment conducted by experts, it was decided to use the concept of fire extinguishing equipment for environmental protection.

Recently, there has been research and development of SiC power devices, and 1,200V SiC-MOSFETs have become commercially available. SiC power devices are suitable for realizing higher voltage applications, and the power devices are connected in series for maintaining the voltage rating. However, the parasitic parameters of the devices are not the same, and it cannot be controlled the voltage sharing. This paper proposes a digital control method for the voltage balancing of series connection SiC-MOSFETs under turn-off operations. In order to compensate the voltage unbalance conditions, this paper presents a time-adjustment gate-drive circuit using an 8-bit programmable delay line. Its performance verified analytically, and experimental results using a buck chopper circuit rated at 1,200V SiC-MOSFETs are presented.

This paper proposes a method for improving the characteristic of the current sensor in a laminated bus bar. The current sensor is embedded in the laminated bus bar and is based on Rogowski coil. The stray components of the laminated bus bar and the sensor may affect the frequency characteristics of the current sensor. Therefore, it is difficult to measure the switching waveforms accurately with the sensor that uses conventional calculation methods. Firstly, the transfer function considering stray components, which is based on the geometry of the sensor, is analyzed in order to evaluate the frequency characteristics of the sensor. Then, the frequency characteristics are improved using an inverse function, which is derived from the transfer function of the sensor, and the inverse function is applied to the calculation method. Finally, the calculation method is verified by conducting a switching experiment, rated at 50V and 8A. It is confirmed that the switching current waveforms that flow through the laminated bus bar can be detected more accurately using the sensor compared with commercial current sensors.

This paper proposes a PWM rectifier with a seamless winding changeover capability. The proposed PWM rectifier can be operated in the star connection mode as well as in the delta connection mode, for which the output voltage is equivalent to a generator with delta winding. The proposed topology is used for open-end winding generators. One of the ports of the generator is connected to a PWM rectifier. Another port is connected to a diode bridge rectifier, which has a switch to short the dc-link of the diode bridge rectifier. The PWM rectifier and the diode bridge rectifier are connected via diodes. The proposed configuration allows seamless winding changeover with reduced number of switches in comparison with a conventional winding changeover circuit. When the delta connection is used, a new control method for achieving low current THD has to be used. The proposed circuit and control are assessed through experiments. The generator current THD of the star connection and the delta connection are 4.0% and 4.7%, respectively. In addition, the transient response is analyzed. In spite of the winding changeover in both the directions, power is continuously supplied to the load.

Novel pulse pattern for PWM double inverters with single shunt current detection to reduce torque ripple of Permanent Magnet Synchronous Motor (PMSM) is proposed. In the proposed pulse pattern, voltage vectors of double inverters at the timing of current detection are adjacent to each other and are changed based on the position of PMSM.

In this paper, the current error and the torque error due to single shunt current detection based on voltage equation of double three-phase wound PMSM are analyzed. Next, the pulse pattern to reduce the torque error is derived. Experimental results demonstrate that the proposed pulse pattern can reduce harmonics of torque waveforms.

A novel circuit topology for a single-phase inverter with a power decoupling capability operated in discontinuous current mode (DCM) is proposed in this paper. An inverter connected to a single-phase grid requires a power decoupling capability to compensate for a power ripple with twice the grid frequency. Bulky capacitors are used as DC-link capacitors in conventional systems. In contrast, the proposed circuit topology can use ceramic capacitors instead of electrolytic capacitors by reducing the required capacitance based on the active buffer concept. Moreover, this active buffer requires no additional inductor because it uses DCM for the power decoupling capability. In this paper, a control method for the active buffer circuit operated in DCM is introduced. An experimental verification of a 1-kW prototype shows that the proposed circuit reduces the input current ripple at twice the grid frequency by 96.8%, with a maximum efficiency of 95.2%. In addition, the Pareto optimization of power density and efficiency is used to clarify the maximum power density points. It is found that the maximum power density of the proposed circuit is 1.6 times higher than that of a conventional boost-type active buffer.

A Z-source inverter (ZSI) can work as an inverter with boost capability in one stage by using its impedance-source and the short-through mode as the switching mode. This paper discusses the circuit losses that depend on the boost ratio between the quasi ZSI, which is one of the ZSI topologies, using SJ-MOSFETs and the conventional inverter with a boost chopper using IGBTs. 2-kW class three phase inverter systems for an AC output of 200V were fabricated using the proposed method and the conventional method, and the losses for each component were analyzed experimentally. Experimental results confirmed that the proposed method can reduce the total loss in low boost ratio operations, in comparison with the conventional method, due to its reduced inverter conduction loss.

This paper proposes a flying-capacitor voltage control method that is independent of the voltage of another flying capacitor, output voltage, and input current for a multi-level flying-capacitor boost DC-DC converter. The proposed method achieves independent control using a new carrier modulation scheme with a minimum number of switching. The validity of the proposed circuit is demonstrated using a simulation.

Voltage-fed inverters have dead-time to protect against short-circuit of the DC-link voltage. Dead-time distorts AC-output voltage and decreases DC-link voltage utilization. To overcome these problems, the authors propose a novel PWM method without voltage error caused by the dead-time of the converter. In this paper, the principle and theoretical operation of the proposed PWM method are described in detail and the theory is confirmed through experiment results.