Osaka Gas (United States)

This paper focuses on the stability issue of power hardware-in-the-loop (PHIL) simulation of inductor coupled systems. Main factors which influence the stability of this type system are analyzed and verified through experiments. A method to resolve the instability problem of the PHIL simulation without decreasing the simulation accuracy is also proposed. Moreover, a PHIL simulation of a gas engine cogeneration system with a matrix converter is introduced and the application of proposed method to improve stability is demonstrated.

As the interest in environmental issues increases, the cogeneration system has recently been attracting much attention. Particularly, the use of gas engines for cogeneration systems with low emission and high thermal efficiency is now expected to become widespread. For improving thermal efficiency, it is necessary to extend the lean limit and accelerate combustion. In this study, attention was focused on "Pre-chamber Spark Plug", which has a pre-chamber at the tip of the standard plug. We studied the effects of using a pre-chamber spark plug for 300kW to 2MW gas engines with a single-cylinder test engine. By the pre-chamber plug, the lean limit was extended and the thermal efficiency was improved.

DC microgrid is a novel power system using dc distribution in order to provide a super high quality power. This dc system is suitable for dc output type distributed generations and energy storages. In this research, we assumed one type of the dc microgrids for residential houses (apartment house or housing complex). Each residence has a distributed generation such as gas engine or fuel cell. Those cogenerations are connected to the dc power line, and the electricity from the generations can be shared among the residences. The hot water from the cogeneration is used in each residence. We constructed an experimental system based on this concept in our laboratory. We have studied the fundamental characteristics and the quality of the supplied power to the loads against several fluctuations or faults. Experimental results demonstrated that the system could supply high quality power to the loads against a sudden load variation and a voltage sag of the utility grid. Afterwards, we moved the experimental system to an experimental apartment house (NEXT21). We studied the quality of the supplying power by using practical power line, and confirmed that the system was also able to supply a power to home appliances stably.

In "Recommended Practice for LNG Aboveground Storage" and "Recommended Practice fo LNG Inground Storage", the allowable compressive stress of knuckle plate is linked to the allowable tensile stress. According to the change of the safety factor of allowable tensile stress in ASME Boiler and Pressure Vessel Code, the safety factor in these Practice has been restudied. In connection with the restudying, the integrity of the knuckle plate is investigated.

Recently, many small sized gas engine cogeneration systems are connected to the grid by way of converter-inverter system. In those cases, AC power generator of a gas engine is connected to the converter and the outlet of the inverter is connected to the grid; generated AC is transformed to DC through the converter and retransformed to AC through the inverter. As the power output point of the system is on the grid line, various expensive grid protection apparatuses are needed, and when power service interruption occurs, some loads like computer trip. If the system is made so that the grid is connected through a converter to DC line of the converter-inverter, the system needs no grid protective apparatus because it only works as a power receiver if looked from the grid. Moreover, the system works as a UPS and the problems above mentioned may be avoided. We made such a system and tested to confirm the possibility.

Recently new ultrasonic flaw detection system called TOFD method is utilized to externally inspect the inner and outer surfaces of weld seams on spherical storage tanks while tanks are in use. In this system, the robot mounted the sensors is not only permitted to travel along the weld seam rapidly but also required to follow the weld seam precisely. In this paper, the development of a magnetic-wheeled robot that can follow the weld seam within 5 mm based on feedback control is described. Since October 1999, this robot has been in experimental operation on an actual spherical tank. Practical introduction of this robot will shorten inspection time by about one week from the conventional 23 days, and will reduce the conventional number of inspectors required from 4 to 2-3.