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Harmonic emissions of variable speed wind turbines (WTs) are a well-known issue, but little information that is based on field measurements on actual machines has been published on the subject. In this paper, the harmonic behavior of modern WTs using extensive measurements performed on commercially available machines is discussed. Specific issues addressed include the shape and the frequency range of the harmonic current spectrum, the variation of the harmonics with the WT operating point, the statistical characteristics of their magnitude and phase angle, the effect of grouping and time-averaging, as well as their symmetrical component characteristics. The objective of the paper is to outline important general characteristics of the harmonic behavior of WTs, rather than to analyze specific machines or compare alternative WT designs. Index Terms--Wind power generation, wind turbines (WTs), harmonics, interharmonics, measurement.

Variable-speed wind turbines inject harmonic currents in the network, which may potentially create voltage distortion problems. In this paper, a case study is presented for a 10-MW wind farm, intended to be connected to a network with extended high-voltage submarine cable lines. First, the system modeling approach and the harmonic load-flow calculation is described. Then, the harmonic impedance of the system is calculated for a variety of configurations and operating conditions, and its main characteristics are discussed. Harmonic load-flow calculations are provided to indicate potential voltage distortion problems. A simplified methodology, suggested in relevant IEC publications, is applied to the system and its results are compared to those of the harmonic load flow. A discussion on the summation of harmonic currents within a wind farm is also included. Index Terms--Harmonics modeling, power system harmonics, summation of harmonics, wind turbines.

Autonomous power systems, such as those existing in small and medium-size islands, typically consist of medium voltage networks fed by conventional power stations and present characteristics not typical for large interconnected grids. In this paper, results are presented and analyzed from a power-quality measurement campaign, conducted in a diesel-powered island system with significant wind penetration. Emphasis is placed on the voltage flicker, which was found quite increased under all operating conditions. It is shown that the diesel engines of the conventional power station are the main source of flicker in the system, due to the pulsed variation of their torque. The operation of the wind farms, on the other hand, does not result in any notable deterioration of the voltage quality level in the system. Index Terms--Diesel-driven generators, flicker, power quality, wind power generation.

Electrical faults and other network disturbances generate transients of the generator electromagnetic torque which result in significant stresses for the wind turbine (WT) mechanical system and may also have a detrimental effect on the fatigue life of important drive train components, such as the gearbox. In this paper, the effect of faults and other disturbances, common in rural medium voltage (MV) distribution systems, is analyzed for a typical fixed speed WT, equipped with an induction generator. The resulting torque transients are evaluated and their propagation in the drive train is examined. Important conclusions are drawn with respect to the type of electrical faults to be considered in the design and certification of WTs according to the current IEC 61400-1 Standard. Although the emphasis is placed on the developed torque transients, the methodology presented is also suitable for analyzing electrical stresses in the generator, due to over-currents or over-voltages. Index Terms--Distribution system faults, induction generators, mechanical stresses, unbalanced operation, wind turbines.

Hybrid power stations (HPSs) are virtual power plants comprising storage and renewable energy source facilities operated in a coordinated manner as dispatchable stations. The HPS concept has been introduced as a means to increase renewable penetration in saturated island systems. The main objective of this study is to shed light on the operation of battery‐based HPSs in small‐island systems and their investment feasibility. Anticipated benefits for the island system are quantified in terms of system production cost and renewable penetration, while the exploitation of available renewable energy by the HPS is analyzed and the internal operation of its components is evaluated. A mixed integer linear programming generation scheduling approach is used to conduct daily and annual simulations of the entire island generation system, while at the same time optimising the internal management of the HPS as well. Based on the operating results thus obtained, the economic feasibility of battery‐based HPS investments using wind, photovoltaics or their combination as the renewable generation component is assessed, by utilising the levelised cost of energy as the primary evaluation index and accounting for the life expectancy of the HPS battery storage system. [ABSTRACT FROM AUTHOR]