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摘要
The grid connection of doubly-fed wind turbines through series compensation capacitors has the risk of causing sub-synchronous oscillations. Therefore, it is necessary to study the effects of rotor-side controllers (RSCs) of wind turbine on sub-synchronous oscillations. In this paper, the control loop of RSC is illustrated in the form of the equivalent circuit, and the influence path of all control parameters from the perspective of the changing properties of system circuit is discussed. The coupling effect between the inner and outer control loops is analyzed. Firstly, through the simultaneous establishment of RSC and induction generator voltage equations, the RSC control is equivalently transformed into the circuit. And the analytical expressions of equivalent power sources and equivalent impedance including all the control parameters of the rotor and phase-locked loop are obtained. Then the corresponding equivalent model of doubly-fed wind turbines is established. Secondly, based on the constructed equivalent model, the direct and indirect impact ways that influence the properties of resistance and reactance respectively are proposed. The coupling interaction effect of the inner and outer loop on the rotor side is analyzed, and the influence mechanism of rotor-side control parameters is obtained. Finally, the correctness and effectiveness of the proposed analysis mechanism are verified by the time-domain simulation and frequency sweeping method. ? 2021 Automation of Electric Power Systems Press.
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