Reseach on an electro-mechanical energy conversion system with small size and 95% efficiency

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The aims of the research are to develope a high efficiency over 97%, small size of 10kW/lit. and high speed of 40000rpm motor/generator, and its efficiency of 97.5% current type power converter.The high efficiency motor/generator is realized by using coreless structure with no-ironloss, high frequency of 1.5kHz which can reduce the number of turns of the winding and He gass to decrease windage-loss. To maintain the gap flux dencity, the neodymium magnet which has high energy production and carbon FRP bands which sustain the magnets, and high speed ceramic bearings must be employed. The coreless structure makes large eddy current loss in the windings and, by using litz wires, it can reduce to under 10%. The motor/generator obtained experimentally is following :6kW 30000rpm 140phi*64 2.8kg efficiency 97.0% (at 5kW output) The planed speed 40000rpm can not be accomplished by rotor distruction.The high efficiency current type inverter/converter which drives its motor/generator is also developed. It is combined a current control chopper and a three phase frequecy changer both of them have high efficiency at high frequency area. The losses in switching devices are divided into two ; onvoltage drop losses and switching losses at on and off times. The former can be decreased by using direct drive method of a transistor and the latter by using current control of the base current or lossless snubber circuits. These techniques are newly developed in this research. 99.2% of chopper efficiency and 98.9% of efficiency of frequecy changer are obtained. As a result, total efficiency of 95.1% is acheived which is slightly larger than planned one.