This research presents a new scheme to extract the maximal available power from a wind turbine employing a doubly fed induction generator (DFIG). This scheme is developed from the wind turbine’s MPPT-curve. Furthermore, we propose control laws for the rotor and grid side-converters. The stability of the proposed maximum available power method and the control laws are proved mathematically upon Lyapunov’s stability criterion. Their efficiency is tested through the simulations of a DFIG wind turbine in Matlab/Simulink. Simulation results are analyzed and compared with that using a conventional scheme. Thanks to the suggested scheme, the wind turbine can track its maximum power point better and the electric energy output is higher comparing with that using the conventional scheme. Furthermore, by the suggested controllers, the rotor speed and current of the DFIG converged to their desired values. In other words, the wind turbine can achieve stable operations by the suggested control laws.
In this paper, author proposed an algorithm to determine method which is used to reduce the fault number caused by lightning on a transmission line. The algorithm is developed based on three methods including increase in the insulator string length, surge arrester installation, and surge arrester installation in combination with increase in the insulator string length. The output of algorithm is the proposed method which makes the number of faults caused by lightning satisfy the requirement and its investment is the cheapest in them. Based on this algorithm, the reasonable method (the number of tower positions needing to improve) to reduce the number of lightning caused faults of the transmission line can determine if we know the ratio of the required number lightning caused faults to the current value. This algorithm is applied to a transmission line to propose an improving method so that the fault number satisfies the requirement. This algorithm is implemented to a 220kV transmission line. The calculation results show the reasonable method and it also indicates in detail which towers should install surge arrester, which towers should increase the insulator string length.
This paper focused on evaluating the application of exponential moving average method into wind turbine to smooth its power output without an energy storage system or an anemometer. Wind turbine control modes including active power control mode and rotor speed control mode are considered. For each control mode, two positions of the Exponential Moving Average method in controller were compared to choose the best position. Additionally, the impact of smoothing factor on wind turbine performance was also considered to determine a reasonable value of the smoothing factor for each control mode. Simulation results in MATLAB/Simulink indicated that, for wind turbine using rotor speed control mode, the Exponential Moving Average method should be applied to reduce the variation of actual rotor speed signal while for wind turbine with the power control mode, it should be used to smooth reference power signal. From the performance of wind turbine with different smoothing factor values, we can suggest that the smoothing factor value should be set at 0.5 and 0.4 for the power control mode and the rotor speed control mode, respectively.
Large offshore wind farms using high voltage direct current transmission system have been considered and exploited in a few countries in the world. Maintaining stable operation of the wind farm is an important issue. Previous studies only proposed some methods to improve the fault ride-through capability of the wind farm as it is connected to a quite strong system, resulting in recovery of the voltage at the point of common coupling (PCC) after clearance of onshore gridfault. This paper will evaluate the PCC voltage recovery ability of the wind farm when it is connected to a weak grid and suggest a new method to overcome unrecoverable voltage problem. The effectiveness of the proposed control strategies is proven by simulation results. V C 2012 American Institute of Physics.
<span lang="EN-US">This research aims to connect wind turbines to a distribution grid to minimize the power loss and to satisfy the grid’s normal operating condition. The proposed algorithm will determine optimal positions, optimal operation mode and wind turbine type. We must choose the best operation mode from available modes including the constant power factor mode and the constant voltage mode. According to the optimal operation mode, we decide the optimal setting data of wind turbine. This algorithm is coded in MATLAB software and implemented to IEEE 33-buses distribution grid. Noted that in this research, we tested two cases including the original IEEE 33-buses grid and its modification where the power system connected to this grid at multi-position. Results indicated that the proposed algorithm could determine the number of wind turbines, position, optimal operation mode, wind turbine type and the priority order of wind turbine installation to minimize power loss. Moreover, results were also compared to that of other algorithms.</span>
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