Akihisa Matsushita

A voltage ratio-based efficiency control method for 3 kW wireless power transmission

This paper presents a novel control method for wireless power transmission (WPT). The proposed method can maximize the power efficiency only by controlling the voltage ratio between the primary and the secondary side. Experimental measurement results of the prototype system with 3 kW power transmission show the efficiency difference between the proposed control method and the available maximum value is less than 0.3 % even with a large variation of coil-to-coil distance and load voltage. The automatic controller for the proposed method provides the load-following operation, maintaining both constant power and high efficiency, using a WLAN connection.

Experimental Verification of Current Source Inverter with ZVS Commutation Circuit

This paper presents a current-source inverter suitable for high-voltage/high-power motor drives. This inverter uses thyristors as main switching devices and utilizes a zero-voltage-switching (ZVS) commutation circuit. It has the advantages of good motor power factor and self-startability. We have evaluated a test model of the proposed inverter and a motor and verified that the inverter operates at a motor power factor of one and that it can be started even when the motor speed is zero. Moreover, a six-phase synchronous motor was driven by two of these inverters; it was confirmed that they decreased the motor torque ripple and the harmonic component of the voltage source. In addition, we evaluated the operation of the ZVS commutation circuit by simulation and experiment and thus verified that turnoff loss depends mainly on the inductance of the ZVS commutation circuit and not on gate resistance. Moreover, when the switching device turns off the current, its voltage is almost zero. That is, even if the inductance is large, the peak voltage of the switching device is low and switching loss is small. Therefore, the ZVS commutation circuit can be easily composed because it does not need to be of low inductance. These results show that a large-capacity drive system can be easily achieved with the proposed inverter.

Inverter circuit with the regenerative passive snubber

This paper presents an inverter circuit using a snubber circuit to achieve soft switching. This snubber circuit has a transformer-based energy regenerative circuit. This circuit has no additional switching device, and the cost is low. In this paper, this circuit was examined and evaluated by single shot test and PWM drive test. By single shot test, turn-on and turn-off waveforms were measured and we verified that the loss of the switching devices was decreased. Moreover by PWM drive test, the temperature under switching devices with snubber was lower than that of snubberless main circuit. Calculating the loss from the temperature, we verified that the total loss of the switching devices decreased to 72%. This decrease of the switching loss will make it possible to raise switching frequency. Therefore, we can reduce the weight of the filter reactor

Novel inverter with zero voltage switching (ZVS) commutation circuit for high-voltage/high-power motor drives

This paper presents a novel inverter suitable for high-voltage/high-power motor drive applications. The proposed inverter has the advantages of high motor power factor and self-startability, which are not realized by a load commutated inverter (LCI) drive. We have evaluated basic performances by using a downsized test system, and verified that the inverter operates at a motor power factor of 1. In addition, for the practical use of the inverter, 13.2kV output composition was verified by simulation. As a result, the proposed inverter achieved expected performances. Moreover we evaluated the operation of the ZVS commutation circuit by experiment, and thus verified that the peak voltage of the switching device is low, and switching loss is small. Therefore, the ZVS commutation circuit can be easily composed because it does not need to be of low inductance. From these results, the proposed inverter with ZVS commutation circuit is suitable for high voltage/high power motor drive applications.