Power-Flow Control and Stability Enhancement of Four Parallel-Operated Offshore Wind Farms Using a Line-Commutated HVDC Link

Abstract

This chapter presents an effective control scheme using a line-commutated high-voltage direct-current (HVDC) link with a designed rectifier-current regulator (RCR) to simultaneously perform both power-fluctuation mitigation and damping improvement of four parallel-operated 80 MW offshore wind farms delivering generated power to a large utility grid. The proposed RCR of the HVDC link is designed by using modal control theory to contribute adequate damping to the studied four offshore wind farms under various wind speeds. A systematic analysis using a frequency-domain approach based on eigenvalue analysis and a time-domain scheme based on nonlinear model simulations is performed to demonstrate the effectiveness of the proposed control scheme. It can be concluded from the simulation results that the proposed HVDC link combined with the designed RCR can not only render adequate damping characteristics to the studied offshore wind farms under various wind speeds but also effectively mitigate power fluctuations of the offshore wind farms under wind-speed disturbance conditions (Wang et al., IEEE Trans Power Delivery 25(2):1190–1202, 2010).

Appendix

1.1 System Parameters

Reference [1]

$$ V_{\text{b}} = 161\, {\text{kV}},S_{\text{b}} = 80\, {\text{MW }}\left( {\text{One of four offshore wind farms}} \right), \, \omega_{\text{b}} = 2\pi f_{\text{b}} ,f_{\text{b}} = 50 {\text{Hz}} $$

• (a) Single 2 MW wind induction generator (IG) (per-unit) $\begin{aligned}& V_{\text{b}} = 6 90 {\kern 1pt} {\text{V}},\,S_{\text{b}} = 2 {\text{MW}}, \, \omega_{\text{b}} = 2\pi f, f_{\text{b}} = 50 {\text{Hz}} \, r_{\text{s}} = 0.00 4 8 8, \\X_{\text{ss}} & = 0.0 9 2 4 1,{\kern 1pt} {\kern 1pt} \,r_{\text{r}} = 0.00 5 4 9, X_{\text{rr}} = 0.0 9 9 5 5,X_{\text{m}} = 3. 9 5 2 7 9,H_{\text{G}} = 3. 5 {\text{s}} \\ \end{aligned}$

• (b) Excitation capacitor bank and AC transmission line (per-unit) $X_{\text{C}} = 0. 3 7 5,R_{\text{T}} = 0.0 1,X_{\text{T}} = 0.0 4,R_{\text{L}} = 0.0 2,X_{\text{L}} = 0.0 8$

• (c) Line-commutated HVDC link (per-unit) $\begin{aligned} R_{\text{DC}} = 0.0 5, X_{\text{DC}} = 0. 2,C_{\text{DC}} = 0. 6,C_{\text{I}} = 0. 3,C_{\text{R}} = 0. 6, \\ T_{\text{a1}} = 0.0 5 {\text{s}},K_{\text{a1}} & = 0. 1,T_{\text{R}} = 0. 1 {\text{s}},K_{\text{R}} = 1.0,T_{\text{I}} = 0. 1 {\text{s}},K_{\text{I}} = 1.0, I_{\text{Cmax}} = 0. 1,I_{\text{Cmin}} = - 0.1, \\ \, \alpha_{\text{Rmax}} = 3 5^\circ , \, \alpha_{\text{Rmin}} = 1 5^\circ , \, \gamma_{\text{Imax}} = 4 5^\circ , \, \gamma_{\text{Imin}} = 2 5^\circ \\ \end{aligned}$

• (d) Wind-turbine characteristics and coefficients

(Fig. 16.11, Table 16.6).

Fig. 16.11

Characteristics of the employed wind turbine model for simulations (©2010 IEEE. Reprinted from IEEE Trans. Power Delivery, vol. 25, no. 2, April 2010) (a) C _P versus ? (b)T _m versus ?_r

Table 16.6 Coefficients c ₁?c ₉ employed in wind-turbine simulations