Abstract
Aiming at the problem of high voltage disconnection when doubly-fed wind farms are merged into weak power grids, this paper researches the theory of rotor excitation control and proposed an additional control model of DFIG grid-connected rotor flux based on structure decentralization theory. In this model, the high voltage ride-through capability for grid-connected wind farms is enhanced by designing the d-axis and q-axis adaptive terminal sliding mode controllers of the synchronous rotating coordinate system. Using the simulation software of MATLAB/Simulink, this paper established a simulation model of wind farm high voltage ride through composed of 2MW doubly fed wind turbines and carried out the off-line simulation of the whole process of high voltage traversing. Real-time simulation experiment of high voltage ride-through was also conducted on a self-developed real-time simulation platform for grid-connected doubly-fed wind farms. Real-time simulation results prove the accuracy of theoretical and offline simulation analysis and the feasibility of control strategy.
Highlights
Most of China’s large wind farms are located in remote areas, away from the load center of the power system, and they are typical weak grid [1], [2]
The results show that under the conventional PI control strategy, when a high voltage fault occurs, the common bus voltage suddenly increases to 0.47 pu, the rotor current is almost constant, and the output reactive power of the doubly fed induction generator (DFIG) is maintained near the given value
This paper mainly takes the grid-connected doubly-fed wind farm as the research object. It proposes an additional sliding mode control strategy for the rotor flux adaptive terminal of doubly-fed wind farm aiming at improving the high voltage traversal performance of the ‘wind-fire’ hybrid transmission system
Summary
Most of China’s large wind farms are located in remote areas, away from the load center of the power system, and they are typical weak grid [1], [2]. Literature [20] deals with the coordinated control of rotor- and grid-side converters in wind turbines with doubly fed induction generators (DFIGs) to improve the low-voltage ride-through capability. Literature [24] proposes the use of doubly-fed induction generator based low-voltage-ride-through scheme including crowbar, rotor-side converter, grid-side converter and power system stabilizers. This paper focuses on the basic grid-connected operation model of DFIG, fully exploits the dynamic characteristics of the rotor flux linkage and its effect on the reactive power of the DFIG output, an adaptive terminal sliding mode additional control strategy for the rotor flux linkage is proposed, which enables the wind farm to quickly absorb excess reactive power during the grid fault to reduce the instantaneous high voltage at the grid bus and improve the quality and stability of the grid-connected voltage of the doubly-fed wind farm.
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