An H∞ robust control of wind turbine (WT) inverters employing an inductor-capacitor-inductor (LCL) filter is proposed in this paper. The controller dynamics are designed for selective harmonic filtering in an offshore transmission network subject to parameter perturbations. Parameter uncertainty in the network originates from the grid and the number of WTs connected. Power converter-based turbines inject harmonic currents, which are attenuated by passive filters. A robust high-order active filter controller is proposed to complement the passive filtering. The H∞ design of the control loop enables desired tracking with integral effect while bounding the induced change. The design was tested in an aggregated model of the London Array offshore wind power plant and compared with traditional Proportional-Integral (PI) controller designs. Robust stability and performance and a reduction of control effort by 25% are obtained over the full envelope of operation.
With the increasing deployment of offshore wind power plants (WPPs), the grid-forming (GFM) battery energy storage system (BESS) has recently emerged as an attractive solution to improve the dynamic performances of WPPs. However, the control interactions of the GFM-BESS and offshore WPP, under different grid strengths, tend to complicate the controllerparameter tuning. This paper presents a modeling method for analyzing control interactions of offshore WPP and GFM-BESS, which sheds clear insights into the critical controller parameters to the system dynamics. Differing from conventional methods, a frequency-domain model of GFM-BESS, obtained by taking the Laplace transform of the corresponding state-space model, is developed first. This allows the impedance model of offshore WPP, including a black-box model of long transmission cable, to be flexibly integrated. Based on the model, both closed-loop transferfunction and pole-based dynamic analyses are then performed. Electromagnetic transient simulations corroborate the effectiveness of the model and analysis.Index Terms-battery energy storage system (BESS), control interaction, grid-forming, offshore wind power plant (WPP)
Abstract-This paper presents an observer backstepping approach to the variable speed control of wind turbines for maximizing wind power capture when operating between cut-in and rated wind speeds. The wind turbine is modeled as a twomass drive-train system controlled by generator torque. The nonlinear controller relies on output feedback backstepping to regulate the generator torque such that a constant tip-speedratio can be obtained. The rotor speed is fed back while torsion angle and generator speed are estimated using a linear observer based on the dynamics of the system. The proposed scheme shows smooth and asymptotic tracking of the rotor speed as illustrated by simulation results.
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