(searched for: doi:10.3390/en11010104)
Energies, Volume 12; doi:10.3390/en12122404
Integration of wind energy into the grid faces a great challenge regarding power quality. The International Electrotechnical Commission (IEC) 61400-21 standard defines the electrical characteristics that need to be assessed in a Wind Turbine (WT), as well as the procedure to measure the disturbances produced by the WT. One of the parameters to be assessed are voltage fluctuations or flicker. To estimate the flicker emission of a Wind Power Plant (WPP), the standard establishes that a quadratic exponent should be used in the summation of the flicker emission of each WT. This exponent was selected based on studies carried out in WPPs with type I and II WTs. Advances in wind turbine technology have reduced their flicker emission, mainly thanks to the implementation of power electronics for the partial or total management of the power injected into the grid. This work is based on measurements from a WPP with 16 type III WTs. The flicker emission of a single WT and of the WPP were calculated. Low flicker emission values at the Point of Common Coupling (PCC) of the WPP were obtained. The flicker estimation at the PCC, based on the measurement from a single WT, was analyzed using different exponents. The results show that a cubic summation performs better than the quadratic one in the estimation of the flicker emission of a WPP with type III WTs.
Energies, Volume 12; doi:10.3390/en12112100
A new topology was recently developed to drive generators, aiming to avoid power electronic devices directly connected to the grid, and making possible the hybridization of the wind power with other sources. The system is composed by an induction machine with rotor in squirrel cage, and a rotating armature endowed with a three-phase winding that may be fed by a secondary source. The previous purpose was to convert a variable velocity imposed by the wind turbine to the armature in a constant velocity to be developed by the cage rotor, driving a shaft of synchronous generator. This article proposes the use of an induction generator instead of a synchronous one in order to explore the maximum available wind energy (MPPT). The simulation results show that the proposed topology is viable and supports both variations in wind speed and disturbances in power grid.
Energies, Volume 11; doi:10.3390/en11092249
This paper presents an in-depth review of classical and state-of-the-art models for analysing the transient stability in wind energy conversion systems. Various transient simulation models for a number of wind turbine generator (WTG) configurations are introduced, under different disturbances. The mitigation is achieved, by manipulating the generator speed and power electronics control, whereas the protection is implemented using conventional, intelligent or digital relays for the safety of sensitive components, in case of transient fault occurrence. The various control systems in WECS are basically employed to transform and regulate the varying frequency, owing to the stochastic nature of wind speed, to the standard 50-Hz or 60-Hz frequency for coupling to an existing electrical utility grid. It has been observed that the control and protection schemes in wind energy systems are concurrently applied. Transient faults in WECSs are a dominant power quality problem especially in the doubly-fed induction generator (DFIG), and often classified as overcurrent or overvoltage transients. These transients are measured using the transient stability index and analysed using the EMTDC/PSCAD software. In addition, the inertia of the rotating masses of wind turbine generators is often characterized by a transient torque, which generates oscillations in power systems.