Development of a High-Performance Induction Generator for Wind Power and Small-Scale Hydropower Plants

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Recently, wind power and small-scale hydropower have been extensively introduced as renewable energy sources that contribute to environmental protection. In such power plants, induction generators are widely used because they can be directly connected to a power grid and do not require much additional equipment while being advantageous in terms of cost and maintenance. However, the induction generators require a magnetizing current from the power grid, which essentially causes a decrease in power factor and efficiency. Therefore, the performance of the induction generators needs further improvement.In this research project, a new type of induction generator termed the "Permanent-Magnet Induction Generator (PMIG)" was developed. The PMIG has a permanent magnet rotor (PM rotor) rotating freely that is mounted within a squirrel-cage rotor linked to the shaft. The stator is the same as that of usual induction generators. A 2.2-kW prototype machine was designed and built. To construct a guideline for creating an optimum design of the PMIG, a technique for the steady-state analysis was also developed. The validity of the developed technique and the practical value of the PMIG were confirmed through experiments performed on the prototype machine. As a result, it was found that the internal self-excitation by the PM rotor contributes to a decrease in the magnetizing current and improves the power factor and efficiency.