The advantages of the variable speed drive of jet-fans have been known from more than twenty years ago. But at present, all jet-fans of the world have been driven at constant speed by the utility power sources. This is because, to realize the induction motor drive through the long cable, some difficult problems must be solved. These problems are the switching surge problem, the EMI problems and the leakage current problems. To solve these problems, we got the sponsorship of the government (MLIT) and started the developments in 2007. And in 2010, we put the variable speed drive of jet-fans into practicaluse. In this paper, the principle of the inverter system for jet-fans, and test results on the actual road tunnel will be presented.
