Paper presents generation system dedicated to small hydro power station. The conventional generation system uses cage induction generator which demand of reactive power is very high and then its power quality in transients and steady state is very poor. To improve the quality of power, a three level NPC power electronic parallel compensator is applied. The generation system reactive current and power is controlled using voltage oriented method. The rotating x-y frame responds space vector of the grid voltage. To prove such system a laboratory 7.5 kW generation stand was built and tested. The NPC three level converter operation was tested in transient condition during turn-on the generator to grid. As result of compensator operation the peak current was reduced. In steady state the compensator produces reactive power demanded by the generator and then the generation system reactive power demand is null.

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Purpose: The purpose of the article is to present a reactive power compensation for small hydropower plants with an induction generator. The classic compensation with capacitors is discussed and its improvement is proposed. Instead of capacitors, a three level power electronic converter connected in parallel to the induction generator can be used to provide reactive power compensation. The purpose of the paper is to present the developed structure of an active compensator and its control method. The developed control method was verified on a laboratory stand. The project and the methods: As part of research, an active compensator was built as a three-level power electronic converter in topology with Neutral Point Clamped. Laboratory tests of a converter compensator were carried out on a stand equipped with an induction generator with a power of 7.5 kW. Laboratory system measurements were made using a power analyzer and an oscilloscope. Results: A control structure of an active compensator based on a voltage-oriented method was presented and discussed. The operation of the con- verter compensator has been verified on a laboratory stand equipped with a 7.5 kW induction generator. The compensator current reduces the reactive (inductive) component of the current consumed from a power grid to a value equal to zero. The reactive power compensator ensures that the tgφ power factor is maintained at a set value of zero, which corresponds to the total compensation of inductive reactive power consumed by an induction generator working in a hydropower plant. Operation of the active compensator did not cause a significant increase in the harmonic content in the current consumed from the power grid. Conclusions: The paper presents the issues regarding reactive power compensation in hydropower plants with induction generators. Commonly used capacitor compensation has been covered and as a result, it is proposed to replace it with power electronics converter compensation of reactive power connected in parallel induction generators. Active compensator provides compensation for the entire reactive power consumed by the induction generator. The use of the converter compensator of reactive power significantly contributes to the reduction of costs for reactive power incurred by the owners of hydropower plants. The reactive power compensator also has a positive impact on the operation of the entire power grid, power losses from the reactive component of the current on the impedances of power grid components are limited. Keywords: renewable source of electricity, reactive power, active compensator, induction generator Type of article: original scientific article

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