Akira Mima

Low phase-to-phase-impedance busbar for modular power converter system

A small modular unit for a power converter system with long lifetime DC-link capacitors is proposed. To reduce the ripple current stress of DC-link capacitors and to improve their lifetime by limiting temperature rises, low phase-to-phase-impedance busbars are selected. Consequently, in a power converter system whose size is 101 L, operating at a rated power of 100 kVA, DC-link capacitors achieve a lower temperature rise of 22 K, which means that the capacitor lifetime can be estimated to be over 15 years.

Development of modular concept uninterruptible power system

Based on a modular design concept, 100 kVA uninterruptible power system using double-sided air-cooled power module has been developed. An efficient air-cooling system suitable for the double-sided cooled power module is developed, and the volume of the converter adopted developed double-sided air-cooling system becomes less than half compared to the conventional converter based on single-sided cooling system. The width of the modular unit composing the rectifier, inverter, and chopper is only 50 mm so as to stack some units side by side in a smaller space and higher maintainability is achieved. The volume as well as the footprint of the developed UPS is smaller than the conventional one by 30 %.

A very thin power conversion unit for equalizing currents through paralleled power modules

Among high power conversion systems, several power modules are often connected in parallel, and ideally should be operated synchronously during their switching. Actually, current imbalances occur due to an asymmetry of current paths on busbars connecting these power modules. This paper deals with the problem of current imbalances between paralleled power modules. First, the general occurrence of imbalanced currents is demonstrated. Next, an original design technique for current equalization in a very thin power conversion unit is presented. Finally, the validity of this proposed principle is shown in simulated results.

Compact gate drive printed circuit board for uninterruptible power system

A gate drive printed circuit board (PCB) was developed for a 50-mm-wide modular-design thin power unit that uses two double-sided cooled power modules in an uninterruptible power system (UPS). A conventional gate drive PCB has a concentrated gate power supply circuit that uses a large transformer and has a conventional pulse open-phase detection circuit that occupies a large mounting area. Thus, the gate drive PCB had to be downsized to make it as narrow as the thin power unit. Consequently, two circuit configurations were proposed to reduce mounting area: one was to decentralizes a gate power supply circuit using a pre-driver with a built-in DC/DC controller and a small distributed transformer, and the other was to downsize the pulse open-phase detection circuit. As a result, the gate drive PCB was downsized to 50 mm × 220 mm, 56 % smaller than the conventional one. Thus, a very thin power unit using a 50-mm-wide PCB was accomplished, and a UPS was developed that is 30 % smaller in volume than the conventional one.