Variable speed drive as an alternative solution for a micro-hydro power plant

Abstract: This diploma work is mainly focused on developing the control strategy for avariable speed drive as an alternative solution to a micro-hydro power plant. The detailed mathematical model for a micro-hydro system including a Kaplan turbine, mechanical shaft and electrical machines is presented and validated through simulations. A control strategy for an autonomous operation of a doubly-fed induction machine-based drive is developed for a wide range of speed. The drive can operate at a unity power factor.The possible applications of the analyzed system are also presented. As a positive side of the system, it is found that the direct interaction between the power electronic converters and the utility grid can be avoided by exploiting the proposed topology, which might lead to a better quality of the produced power in terms of harmonics. This could also lead to removal or reduction of the size of the harmonic filters that are being used in conventional doubly-fed induction generator installations. As regards to the drawbacks of the system, a comparison of converter and generator ratings between the analyzed solution and the conventional solution was performed. While the converters rating remain the same, there is one more electrical machine and the doubly-fed generator rating is slightly increased. Losses are also slightly larger due to the presence of the second machine.