Abstract
A method to suppress sub/super-synchronous oscillation of direct-drive wind turbines based on energy compensation is proposed. First, the transient energy model of direct-drive wind turbine is built, and the negative damping energy terms that lead the oscillation of direct-drive wind turbine are extracted. On this basis, the expressions of voltage compensation terms corresponding to negative damping energy terms are derived by backward deduction, thus supplementary energy branches are constructed, and their impact on fundamental frequency characteristics of wind turbine is analyzed. And then, with the compensation energy of supplementary branches reaching the maximum and the increment of fundamental-frequency voltage being the minimum as the objective, and with the frequency-domain characteristic and fundamental-frequency voltage characteristic of control links being satisfied as constraints, a scheme to optimize the compensation coefficients of multiple branches is established. Finally, the model of direct-drive wind turbine is built in RT-LAB for hardware-in-the-loop tests. Simulation results verify that, the method can realize fast frequency-dependent suppression of sub/super-synchronous oscillation in different frequency bands concerning different grid strengths.
Highlights
As the percentage of permanent magnet synchronous generators (PMSG) in the installed capacity of local areas rapidly increases, sub/super-synchronous oscillation caused by the integration of PMSG to weak power grid via inverter occurs ever more frequently [1–4], greatly intimidating the safe and stable operation of power grid
The method of adjusting controller structure [5–9] is based on the existing inverter control links, and the dynamic characteristics of wind turbines are changed by improving the control link structure of the wind turbine current inner loop controller, DC voltage outer loop controller, and PLL controller
It can be seen from Equations (30)–(32) that, in fundamental frequency, supplementary branches VP2 and VI1 mainly affect d-axis current inner-loop control, weakening PI steadystate error control of current inner loop, they will affect the fundamental-frequency voltage of wind turbine
Summary
As the percentage of permanent magnet synchronous generators (PMSG) in the installed capacity of local areas rapidly increases, sub/super-synchronous oscillation caused by the integration of PMSG to weak power grid via inverter occurs ever more frequently [1–4], greatly intimidating the safe and stable operation of power grid. The method of adjusting controller structure [5–9] is based on the existing inverter control links, and the dynamic characteristics of wind turbines are changed by improving the control link structure of the wind turbine current inner loop controller, DC voltage outer loop controller, and PLL controller This method can achieve online oscillation suppression and has a good suppression effect for different types of oscillations. The method of optimizing controller parameters [15–19] is to maximize the damping ratio of the interconnected system by coordinating and optimizing the control parameters of the wind turbine generator-side controller (MSC) and the grid-side controller (GSC), thereby changing the resonance point of the oscillation of the wind power system and the grid interaction This method can fundamentally reduce the risk of system instability. The model of system is built in RT-LAB for simulation tests, and simulation results verify the correctness and effectiveness of the proposed method
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