Power electronics and its applications to renewable energy in Japan

Abstract

The electric utility industry is gradually undergoing restructuring and the main paradigm shift is the introduction of the principles of competition. With the level of future demand for electricity being unclear, power market players are reluctant to commit to long-term capital investment, with the result that construction of new large-scale power plants and also transmission and distribution infrastructure is typically being avoided. At the same time, power facilities are being upgraded in response to business strategies for bringing a profit in power markets and for keeping supply reliability for customers. Under such circumstances of competitive power markets, practical use of renewable and distributed energy generation offers an attractive alternative for power supply. The advantages include a short construction cycle as the supply can be located near to the demand, being less of a burden to the existing transmission network, and contributing to prevention of global warming through clean combustion using novel energy technologies such as natural gas co-generation, natural gas micro turbines, or fuel cells. Distributed generations using renewable energy resources such as wind and solar energy are also attracting attention. Regarding practical use of renewal energy in Japan, a new set of requirements advents. The first is the development of a set of policies for promoting power generated from renewable energy. The second is to evaluate the influence of distributed generations from renewable energy on the quality and reliability of the electricity. The third is the establishment of the technology requirements for interconnection with the power grid. The fourth is the development of future energy supply networks such as Power parks, Microgrids, and Smart grids. In implementing future energy supply networks utilizing renewable energy, power electronic devices are widely used to interface some forms of renewable energy generations and energy storages to distribution networks, and their use is likely to increase remarkably in the near future. The development of these power electronics is benefiting from the rapid advancements in the capability of power semiconductor switching devices and in the progress being made in the design and control of variable-speed drives for large motors. The most diffused application of power electronic devices is to invert the DC generated from some dispersed energy resources (e.g. photo voltaic fuel cells, micro turbines and battery storages) to existing 50/60 Hz AC. Also, power electronic devices are used to decouple rotating generates from the network and so potentially increase the efficiency of the operation of the prime mover by ensuring that they operate at their most efficient speed for the range of input power. For example, power electronics are used to support variable-speed wind turbines and are also now being proposed for some forms of small hydro-generation and energy storages during transients. In this article, we will discuss the role of power electronics for renewable energy utilizations and the kinds of infrastructure that should be designed and how this should be pursued in order to maintain high reliability and quality for future energy supply networks in the restructured electricity markets.