Stability analysis and a hybrid controller design of grid‐connected offshore wind farm through a VSC‐HVDC transmission link

Abstract

This paper proposes a hybrid controller which is a combination sliding mode control and PI control techniques for AC grid integrated offshore wind farm (OSWF) with voltage source converter -high voltage direct current system. The controller must be capable of controlling AC voltage, DC-link voltage, reactive power and effective power transfer. To examine the FRT capability, a symmetrical fault is applied at onshore AC grid side and compared the performances of the studied system based on the hybrid and PI controllers. The dynamic modelling and linearized system by state-space modelling for the studied system are explained in detail. The small signal stability analysis and controller stability are observed with the help of the eigenvalue analysis. The analysis of the studied system with a hybrid and conventional controllers are conducted in the software environment of the MATLAB/SIMULINK. The effect of parameter uncertainty on total system stability is examined with the help of eigenmatrix of the studied system.

Wind energy conversion system under asymmetrical voltage failures: Analysis and nonlinear control

“…Other important issues to be taken into account for comparisons are the whole closed-loop system stability and the overall control complexity. Regarding the DC link voltage deviation and its dynamical behavior, the present proposal obtains, under symmetrical voltage failures, better results (maximum voltage deviation percentage and duration) than the ones shown in Dey et al [9] and Srikakulapu and Vinatha [14] and a behavior similar to the obtained in Xing et al [11] and Babaghorbani et al [18]. It is important to say that most of these articles do not present simulation results under asymmetrical voltage faults, and therefore, it is not possible to determine the robustness of these control proposals.…”

“…It should be noted that in Figure 4, dynamic expressions and blocks are related in the next way: Turbine and PMSG represent expressions (3)(4)(5)(6), DC link corresponds to (14), GCD + Line Filter indicates ( 8) and ( 9), Grid Power + Losses takes into account the resistive part of ( 8) and ( 9) and ( 11)and (12). Finally, PSC + SGSC means PSC in the converter at the PMSG side and DC link Control and GSC Control indicate Lyapunov Control at DC and at grid sides, respectively.…”

“…New grid connection codes specifically require that WECS provide grid support in cases of abnormal conditions [5], with special stress in operation under unbalanced grid voltages [6]. In this sense, many interesting contributions about WECS operating under symmetrical and asymmetrical grid failures have been published in the specialized literature during the last years [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22]. In the particular case of PMSG-WECS, most of these approaches propose, during such grid voltage failures, reducing the wind power extraction at the generator side converter while delivering at the grid side the power required by the net despite the distorted voltage presence [7].…”

“…Besides, this technique neither presents robustness features against external perturbations or system model inaccuracies, feature that can be dangerous in the present context. To overcome these kind of disadvantages, some current contributions combine this control framework with more sophisticated control environments like feedback linearization [13], sliding modes [14], or fuzzy logic techniques [15]. These sort of control synthesis produces complex controllers that, despite they can deal with nonlinearities and external perturbations, require heavy computational burden.…”

Switching stabilising control of VSC‐HVDC transmission systems

“…However, this improvement makes the stability of the system very sensitive to the controller parameters when the system has a very small short‐circuit ratio. To avoid the influence of the control parameters, the authors in [20–24] designed new controller or improved the original controller to improve the stability of the system by sacrificing the quick response characteristics of the converter, but this approach is not suitable for AC system with great inertia. In addition, overly complex control algorithms are not easy to implement in engineering applications.…”