One of the most important and efficient sources of green electricity is catching air currents through wind turbine technology. Wind power plants are located in areas where the energy potential of the wind is high but it varies. The time variation of the wind generates fluctuations in the power produced by the wind farms that is injected into the grid. This elevates, depending on the intensity, problems of network stability and the need for balancing energy, thus raising both technical and cost issues. The present paper analyzes the behavior of a wind turbine (WT) over time in varying wind speed conditions, highlighting that without automation algorithms, a WT is far from the operation at the maximum power point (MPP). However, even when it is brought to operate at MPP, there are still significant variations in the power injected into the network. These power variations can be compensated if the wind system has energy storage facilities for the captured wind. All of these assumptions are analyzed using improved mathematical models and processed in simulations, with experimental data used as input from a wind turbine with an installed power of 2.5 [MW] in operation on the Romanian Black Sea coastal area. Consequently, the paper demonstrates that during an operation in the optimal area, from an energy perspective, the wind turbine’s maximum power point requires a storage system for the captured wind energy.

This work presents the limits of mathematical models of wind turbines. At a wind turbine, WT, in the region of negative powers, Pwt, usual mathematical models are no longer valid, the errors being unacceptably high, the obtained values are much different from real values. In the area of positive power, the mathematical models are valid and approach to the real power characteristics. These considerations are especially useful in making accurate simulations of different operating regimes. In the maximum power point area — MPP, the models can be used with good results, but only at constant wind speed. For large angular mechanical velocity (AMV), over AMV at without load, Ouai, these models can no longer be applied. The mathematical models are very useful in various simulations and are therefore used, both, in the design — construction phases as well as in operation.

The modern, developed society becomes aware of the necessity to conserve and protect the environment, increasing the gained benefits from a rational use of the natural resources. The pollution and the limitation of the fossil fuels, associated with the political situation worldwide that affects direct the energy strategies, have opened opportunities in the area of operation renewable energy sources. The development of the exploitation of renewable energy sources is directly linked to the energy politic, which, in terms of Romania, has the focus to integrate into the European Union energy strategy. The year 2014 brought in Romania many legislative changes to the renewable support scheme, that proves, once again, the legislative unpredictability and limitations introduced by the legislator "during the game" that overthrew all economic profitability calculation of the existent and planned investments in this sector. The actual stage of the wind energy across Europe and the particular situation in Romania are highlighted; also a 2020 forecast for Romania tries to evaluate the perspective for the wind, and general, renewable energy market. The actual Romanian renewable energy support scheme, mainly regulated by "Law 220/2008" ends December 2016. The so-called "ready to build" projects especially wind- or hydropower, can't be finalized until this deadline, being unable to qualify to the existing, mainly to inoperable, support scheme. Another legislation that has to clarify how investments in renewable energy will be supported is still not in place, blocking any project development, implementation and economical benefit of the producer. The paper presents in this respect an updated overview of the Romanian renewable energy sector and its perspective.

The conversion of air currents through wind turbine technology stands as one of the most significant and effective means of generating green electricity. Wind turbines featuring a horizontal axis exhibit the greatest installed capacity. The study establishes a mathematical model for large wind turbines, categorized by megawatt output, utilizing measured data for key parameters, including wind speed, power output from the generator, and rotational speed. The analysis of the system’s behavior on startup—the cut-in wind speed, is conducted by transitioning the electric generator into motor mode. A mathematical model has been established for the dual-powered motor configuration, wherein both the stator and rotor are connected to a common frequency network, facilitating a shift to synchronous motor functionality. The equation that describes the kinetic moment highlights the importance of attaining optimal velocity, while simultaneously accounting for variations in the load angle. These fluctuations are observable in both the power output and the electrical currents. The simulations that have been processed are derived from experimental data, specifically inputs obtained from a 1.5 MW wind turbine located in the Oravita region of southwestern Romania. The paper thus outlines essential elements concerning the functionality of high-power wind turbines that utilize wound rotor induction generators, aiming to guarantee optimal performance from the moment the wind speed reaches the cut-in threshold.

Vector control methods offer the possibility to gain high performance, being widely used. Certain applications require an optimum control in limit operating conditions, as, at maximum torque, that is not always satisfied. The paper presents how the voltage and the frequency for an asynchronous machine (ASM) operating at variable speed are determinate, with an accent on the method that keeps the rotor flux constant. The simulation analyses consider three load types: variable torque and speed, variable torque and constant speed, constant torque and variable speed. The final values of frequency and voltage are obtained through the proposed control schemes with one controller using the simulation language based on the Maple module. The dynamic analysis of the system is done for the case with P and PI controller and allows conclusions on the proposed method, which can have different applications, as the ASM in wind turbines.