Ikuo Yamato

New conversion system for UPS using high frequency link

A novel conversion system for a UPS (uninterruptible power supply) using a high-frequency link is described. The UPS consists of a high-frequency inverter and transformer and a cycloconverter. The cycloconverter can be operated by both source commutation and self-commutation (by turning off the switching devices). A choice is made between the two commutation methods, depending on switching device losses during commutation and the internal voltage drop caused by commutating reactance. A compact and efficient UPS can be realized with this conversion system.<<ETX>>

High frequency link DC-AC converter for UPS with a new voltage clamper

A power conversion system for a UPS (uninterruptible power supply) using a high-frequency link is described. The proposed UPS consists of a high-frequency inverter, a high-frequency transformer, and a cycloconverter with a new voltage clamper. The clamper effectively reduces the power loss of the conversion system. The voltage clamper gave an improved DC-AC conversion efficiency of about 10% more than when a conventional RC snubber was used. When source-commutation was used, DC-AC conversion efficiency was improved by about 5%. When the voltage clamper was used both DC-AC conversion efficiency and the output voltage characteristic without the automatic voltage regulator were improved to source commutation. Fabrication of a 10 kVA high-frequency-link DC-AC power converter is described and its loss reduction effect is demonstrated.<<ETX>>

Highly efficient contactless electrical energy transmission system

This paper proposes a new concept for a contactless electrical energy transmission system for an automated guided vehicle. The system has rechargeable batteries on the vehicle and electrical energy is supplied at a specific place. When electric power is supplied to the vehicle, it runs automatically and approaches the battery charger. Therefore, a comparatively large gap is needed between the primary transformer at the battery charger and the secondary transformer on the vehicle in order to prevent damage which would be caused by a collision. In this case, a drop of the transformer coupling rate due to the large gap must be prevented. In conventional contactless electrical energy transmission technology, since electric power is received by a pick-up coil from a power line, a large-sized transformer is required. And when the distance over which the car runs is long, the copper loss of the line also increases. The developed system adopts a high frequency inverter using a soft switching method to miniaturize the transformer. The system has a coupling rate of 0.88 for a transformer gap length of 10 mm and can operate at 91% efficiency.

Power loss reduction techniques for three phase high frequency link DC-AC converter

A three phase high frequency link DC-AC power converter suitable for UPS (uninterruptible power system) applications is described. This converter consists of a high frequency inverter, a high frequency transformer, and a cycloconverter. Power loss reduction techniques for the cycloconverter are discussed, which include zero voltage switching, source commutation, and a voltage clamper. Fabrication of a 3 kVA high frequency link DC-AC power converter is described and its loss reduction effect is demonstrated.<<ETX>>