Development of a Permanent-Magnet Induction Generator for Wind Power and Small-Scale Hydropower Applications

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Recently, wind power and small-scale hydropower plants have been extensively introduced as renewable energy sources that contribute to environmental protection. In such power plants, induction generators (IGs) 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 IGs require a magnetizing current from the power grid, which essentially causes a decrease in power factor and efficiency. Therefore, the performance of the IGs needs further improvement.In this research project, a new type of IG termed the Permanent-Magnet Induction Generator (PMIG) was developed, and its electric and magnetic characteristics were analyzed. The PMIG has a permanent-magnet (PM) rotor inside a squirrel-cage rotor. The squin-el-cage rotor is linked to the shaft, and the PM rotor is free to rotate against the shaft.As a result of the analysis, the following new findings were obtained :1.The desired operation as an IG is not obtained when a damper function is added to the PM rotor.2.Even if the PMIG operates at unbalanced voltages or single-phase power grids, its efficiency is better than that of a conventional IG3.Since the negative-sequence rotating field, which is produced under unbalanced modes of operation, is almost canceled by the squirrel-cage rotor, there is no risk of PM's demagnetization.