Abstract
Nowadays, most of the doubly fed induction generators (DFIGs) are equipped with rotor crowbar for the requirement of low voltage ride through (LVRT). The crowbar resistance is an important parameter, and it is selected taking rotor overcurrent and dc link overvoltage limits into consideration. However, the impact of grid impedance on the LVRT performance of DFIG and crowbar resistance is not adequately researched. This paper proposed an improved method to analyze the LVRT performance of DFIG system with rotor crowbar taking the influence of the grid impedance to fill this gap. The impedance of the present grid would be decreased in the future due to the installation of more wind farms to the grid. As a consequence, the performance of DFIG under LVRT with rotor crowbar is degraded. So the design rules of the crowbar resistance need to be reconstructed. Additionally, the analytical expression of the crowbar resistance is derived considering the grid impedance. The effectiveness of the proposed method is validated through theoretical analysis and MATLAB simulations.
Highlights
In recent years, wind power plays a significant role in the power system due to the high penetration of wind energy into the power grid
The wind energy conversion system should meet the requirements of the grid voltage control, and this is termed as fault ride-through or low voltage ride- through (LVRT) to guarantee the stability of power system in grid faults scenarios
The stator currents under 90% grid voltage dip are simulated with the crowbar resistance selected by different methods, and the simulation results are given in Fig. 16, where the amplitude of the stator current is plotted against time
Summary
Wind power plays a significant role in the power system due to the high penetration of wind energy into the power grid. Most of the hardware based protection schemes for a wind turbine in the industry deployed the crowbar to limit the high current and voltage in the rotor circuit [8]–[10]. This paper analyzed the impact of grid impedance on the LVRT performance of the DFIG system with rotor crowbar solutions. MODELING The DFIG system includes a wind turbine, drive train model, the generator, back to back power converter together with its control system and connects with the grid through the transformer (See Fig. 2). The WT level generates the reference value for the rotor speed of the DFIG based on the measured wind speed and optimum power-speed characteristic curve It controls the output mechanical power of the wind turbine through the pitch angle. The converter control, i.e., the controllers of RSC and GSC, decouple the active and reactive power and will be briefly introduced in the forthcoming sections of this paper
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