Naoya Takahashi

Parallel Bi-directional DC-DC converter for energy storage system

A scalable parallel bidirectional DC-DC converter system has been developed and evaluated. Fast and efficient seamless control is achieved by using an H-bridge topology. Although the control structure is simple, four drive modes can be handled. It was extended for use in simple parallel converter management. A parallel function auto-rotation scheme is used to control which units are active on the basis of tracked power. This method achieves high efficiency over a wide load range, especially for light loads. The automatic rotation of which converter acts as the output master distributes the load more evenly, resulting in less load damage. The only hardware required are a power line and communication cable connection. All other functions are provided by software and operate autonomously. A 5-kW prototype converter was constructed and evaluated in a three-unit parallel converter system. The estimated efficiency for 15-kW rated discharge was 97.8% for 333-V battery pack power and 380-V DC-link power.

Stable startup of seamless controlled parallel bidirectional DC-DC converter

A smart control method for Bidirectional DC-DC Converter has been developed. Both charge and discharge with buck / boost mode transition are achieved by common control structure without mode judgment. This simple structure is also extended to a parallel system, and controls multiple output power for both directions. The function has some exceptional case at the period of start-up and stop, because introduced complementary switching flows unexpected reverse current. To avoid the unexpected reverse current, we introduced the selective disable function of complementary switching and achieved stable start and stop control. This improvement also equipped the system additional charge only operation. Improved control structure was evaluated at the four-parallel converter system.

Seamless controlled parallel bi-directional DC-DC converter for energy storage system

A scalable parallel bidirectional DC-DC converter system, which enables efficient seamless control using an H-bridge topology, was developed and evaluated. Although the unified control structure is simple, four drive-mode, both charge and discharge with buck/boost, can be handled. The proposed system was extended for use in simple parallel converter management. This scheme achieves high efficiency over a wide load range, especially for light loads. The only hardware required is a power line and communication cable connection. All other functions are provided by software and operate autonomously. A 5-kW prototype converter was constructed and evaluated, and a four-unit parallel converter system was tested and confirmed to work well, changing load between 20-kW discharge and 20-kW charge.

Performance improvement of jukebox-type optical disk file system

This paper proposes an image data prefetch method for improving the performance of client/server optical disk file systems that use a jukebox-type optical disk equipment. The frequent optical disk replacement of the jukebox has been the cause of the delayed data access of the file server, and an intolerable long response time at workstations. To reduce the frequency of disk replacement, the proposed method prefetches a series of image data from the file server to workstations for possible later displaying or printing. This method is implemented in a commercial system, and its performance is better in comparison with a conventional system. A concurrent processing function also is implemented in the file server. It enabled a waiting time for the disk replacement to be used for the services for other workstations. This also contributed to an additional performance improvement.