This paper proposes a method of retaining high enough voltage on the terminal of DFIG wind turbines during a fault interval on the connected grid. This method is developed by the ideal of dynamic voltage restorer equipment and was applied to a wind turbines group. The DC-link and the grid side converter of the first DFIG wind turbine in this group are utilized to support the other wind turbines. The converter is connected to a transformer, which is in series with the wind turbine group and the connected line, during an external fault. At the DC-link of the back-to-back converter of each DFIG wind turbine, a DC chopper is equipped to dissipate excessive active power during the fault interval. Moreover, the controllers of all wind turbines are modified to support all wind turbines in the group. The method is verified by MATLAB/Simulink. Simulation results implied that the proposed method can retain a high enough voltage on the terminal of DFIG while preventing overcurrent on the rotor side.

This paper aims to compare the performance of frequency regulation with two control modes of controller including power control scheme and rotor speed control scheme. The frequency control in this research is based on the frequency droop control method but fuzzy logic is used to define the frequency droop coefficient. To compare the performance of these control modes, a simulation of a micro-grid with the existence of a group of doubly fed induction generator wind turbine system and a diesel generator is fulfilled in Matlab/Simulink. Simulation results indicated that the frequency in the micro-grid with two control schemes always remains in the operation range. With the power control scheme, the frequency in the micro-grid is smoother than that with the rotor speed control. Additionally, DFIG wind turbine with the power control scheme has a better performance in terms of electrical energy when compared to the rotor speed control scheme, and hence the cost of fuel used by diesel is less costly.

Reactive power plays an important role in the operation of power systems, especially in the case of wind energy integration. This paper aims to evaluate the reactive power support capability of wind turbines in both normal and voltage sag conditions. The three 2MW wind turbines studied are a fixed speed wind turbine and two variable speed wind turbines with full-scale and power-scale power converters. Comparison results indicate that at normal operation, the fixed speed wind turbine with a static synchronous compensator is able to consume the highest reactive power, while the variable speed wind turbine with full-scale power converter can supply the highest reactive power. In case of low voltage, the fixed speed wind turbine with the static synchronous compensator can support the highest reactive power if the static synchronous compensator’s capacity is similar to the wind turbine’s capacity, while if its capacity is equal to 25% of the generator’s capacity, the variable speed wind turbine with full-scale power converter has the best performance.

This paper proposes a new scheme to reduce the output power variation range of a wind turbine group without an energy storage system. This proposal is based on the active power compensation principle for each wind turbine. In this research, the wind turbine operates in the active power control mode. The reference active power is calculated in such a way that it compensates for the difference between the average output power and the actual output power. To verify and evaluate the proposed method, we simulated a group of two 1.5MW-wind turbines in the Simulink environment of MATLAB. Simulation results were compared to the ones of a wind turbine group without any smoothing scheme and the ones of the same group with the Exponential Moving Average method. From this comparison, we can conclude that with the proposed method, the actual output power of the wind turbine group becomes smoother than that of the wind turbine group without any smoothing scheme. Moreover, the performance of the wind turbine group with the proposed method is better than that of the wind turbine group with the Exponential Moving Average method.

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