A systematic methodology for smooth connection of wind-turbine-driven doubly fed induction generators (DFIGs) to the grid is presented. Synchronization of the voltage induced in the DFIG open stator to that of the grid, which needs to be accomplished prior to connection, is thoroughly examined. A particular grid-voltage-oriented rotor control scheme is considered for this purpose. Generic tuning equations for the rotor current integralproportional (I-P) controllers involved in this scheme are also derived. Transition between the control configurations devoted to synchronization and normal operation-active power generation and reactive power interchange with the grid-at the instant of connection is studied in detail. Mainly due to the reference frame selected for synchronization, the greater part of this transition takes place naturally. However, given that the rotor current dynamics vary significantly depending on whether the DFIG stator is connected to the grid or not, the parameters of the I-P controllers involved in both schemes will accordingly be different. Consequently, a "bumpless" strategy is provided that preserves the smoothness of the connection. A simple method for initial rotor positioning, required when performing vector control based on an incremental encoder, is also suggested. The resulting overall methodology is validated on a 7-kW DFIG-based laboratory-scale test bench.Index Terms-Doubly fed induction generators (DFIGs), industrial power system control, initial rotor positioning, smooth connection, synchronization, vector control, wind power generation. NOMENCLATURE -Subscript. ı m s Stator magnetizing current space phasor. i r , i s Rotor and stator direct-or quadratureaxis current components, expressed in a particular reference frame. ı r , ı s Rotor and stator current space phasors, expressed in a particular reference frame. L m , L r , L s Magnetizing, rotor, and stator inductances. L rRotor transient inductance. P s , Q s Stator-side active and reactive powers.

This paper describes a new technology, the active earthing system, based on a multi-frequency power converter, which combines a new power electronic device with a protection and control system. This system allows network enhanced operation and maintenance, overcoming some of the limitations of the traditional earthing systems, giving rise to relevant improvement in supply continuity.

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This paper shows an analysis of the methodologies used to detect the islanding operating of the three-phase grid connected photovoltaic inverters. In some countries, the operating regulation before islanding conditions is not specified enough. Now the new operating procedures try to integrate the guidelines which the distributed generating systems must follow in order to reach an optimum operation under islanding conditions. Nevertheless, there is still a lack of regulation in this sense. In order to analyze the different detection methods, some simulations have been carried out. This document pretends to establish a test guideline, necessary to validate the islanding detection systems which are integrated inside the photovoltaic inverters, in order to ensure a correct operation of them. That is why the results of real tests of JEMA's photovoltaic inverters have been included.