Abstract
This paper investigates the use of an Electronic Power Transformer (EPT) incorporated with an energy storage system to smooth the wind power fluctuations and enhance the low voltage ride-through (LVRT) capability of directly driven wind turbines with permanent magnet synchronous generators (D-PMSGs). The decoupled control schemes of the system, including the grid side converter control scheme, generator side converter control scheme and the control scheme of the energy storage system, are presented in detail. Under normal operating conditions, the energy storage system absorbs the high frequency component of the D-PMSG output power to smooth the wind power fluctuations. Under grid fault conditions, the energy storage system absorbs the redundant power, which could not be transferred to the grid by the EPT, to help the D-PMSG to ride through low voltage conditions. This coordinated control strategy is validated by simulation studies using MATLAB/Simulink. With the proposed control strategy, the output wind power quality is improved and the D-PMSG can ride through severe grid fault conditions.
Highlights
With the increasing urgency of both energy crisis and environmental pollution, there is a pressing urgent need to find alternative fuel sources which are clean, environmental-friendly and reproducible.Wind power is assumed to offer the most favorable technical and economic prospects in this respect, and is the most rapidly growing one among the various renewable energy sources [1,2].There are mainly two kinds of wind power generators in wind farms, directly driven wind turbines with permanent magnet synchronous generators (D-PMSGs) and doubly fed induction generators (DFIGs)
Output power Pgen increase from 0.523 to 1.0 pu in less than 2 s after the wind speed steps, while the power transferred to the grid Pgrid increases more slowly and the redundant power is absorbed by the super-capacitor stack, the reactive power transferred to the grid by Electronic Power Transformer (EPT) is kept at 0 pu during all the simulation time
Wind power with turbulence is used to test the power smoothing performance of the energy storage system under normal conditions, where the active power data of the D-PMSG is obtained from a wind farm located in central China
Summary
With the increasing urgency of both energy crisis and environmental pollution, there is a pressing urgent need to find alternative fuel sources which are clean, environmental-friendly and reproducible. Especially under grid fault conditions, and if the wind power generators trip offline for self-protection, this will deteriorate the grid conditions and make the grid more difficult to recover [4] To address these issues, on the one hand, wind farms generally need to install reactive power compensation devices, such as Static VAR (volt ampere reactive) compensators (SVCs), static compensators (STATCOMs) etc., for wind generators to provide quick reactive power compensation and grid voltage support [5,6,7]; on the other hand, some control strategies based on the wind turbine pitch angle control or energy storage system have been proposed to smooth the wind power fluctuations or enhance the low voltage ride-through (LVRT) capability of wind generators [8]. Phase ground fault conditions are conducted to verify the effectiveness of the proposed control strategy using MATLAB /Simulink
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