Higher harmonics of converter currents in energy conversion system of small water plants

Energy in small water plants is produced by PM synchronous generators which quite often work at variable rotation speed. This energy has to be converted by means of a power electronic unit to fit to the three-phase power grid parameters (3 × 400 V, 50 Hz). The main purpose of the control strategy is to transfer maximum possible amount of energy, produced by the hydro-set, to the power grid. The second purpose of the control strategy is to decrease the amount of higher harmonics in converter currents. The Total Harmonic Distortion factor depends on the assumed method of transistor switching in power electronic converters. This paper presents the comparison of current harmonics for two chosen basic methods of transistor switching in energy conversion system.