Sliding Mode Controller Design for Wind Energy System to Enhance Power Profile and Stability

Abstract

This study proposes a sliding mode control (SMC)-based control strategy to minimize wind power fluctuation against wind turbulence variation. Due to unpredictive nature of wind, the wind turbulence thrust varies from specified low to high limit. As a result, it gives advisable effect on system grid inertia, stability and wind energy system components such as blades, gearbox, etc. Hence, the proposed control strategy reduces wind power oscillations in coordination with optimal pitch control mechanism by the use of wind power error and generator speed error signal. A variable system damping characteristics is achieved using nonlinear function and switching plane against wind uncertainty and its parameter is calculated by application of linear matrix inequality optimization tools. The control scheme strategy converges asymptotically and ensures system stability. Thus, wind power remains invariance against wind turbulence thrust change. MATLAB^© simulations are demonstrated on 3.6 MW wind energy system and also compared with existing controller to illustrate effectiveness of the proposed control strategy.

Appendix: Wind Energy System Matrices and Its Parameters

$$\begin{aligned} & A = \left[ {\begin{array}{*{20}c} { - \frac{{(B_{t} + B_{{tR}} )}}{{2H_{R} }}} & { - \frac{1}{{2H_{t} }}} & {\frac{{B_{{tR}} }}{{2H_{t} }}} \\ { - K_{{tg}} } & 0 & { - K_{{tg}} } \\ {\frac{{B_{{tR}} }}{{2H_{R} }}} & {\frac{1}{{2H_{R} }}} & {\frac{{(B_{t} + B_{{tR}} )}}{{2H_{R} }}} \\ \end{array} } \right],B = \left[ {\begin{array}{*{20}c} 0 \\ 0 \\ { - \frac{1}{{2H_{R} }}} \\ \end{array} } \right],F = \left[ {\begin{array}{*{20}c} 0 \\ 0 \\ {\frac{1}{{2H_{t} }}} \\ \end{array} } \right],\\ & C = \left[ {\begin{array}{*{20}c} 1 & 0 & 0 \\ 0 & 1 & 0 \\ \end{array} } \right],x = \left[ {\begin{array}{*{20}c} {\omega _{t} } & {\omega _{r} } & {\Gamma _{{tg}} } \\ \end{array} } \right]^{T} \end{aligned}$$

Rated capacity: 3.6 MW; number of blades: 3; blade diameter: 104 m; wind speed (variable): 8–13 m/s; cut-in wind speed: 5 m/s; cut-out wind speed: 27 m/s; mechanical shaft system (on 3.6 MW base): H^t = 2.49 s; H_g = 0.9 s; D_t = D_g = 0; D_tg = 1.5; K_tg = 296.7 pu. λ^opt = 6.212 pu; ω_base = 1.335 pu; C_p^out = 0.4288 pu; ω_r^max = 1.33 pu; ω_r^min = 0.7 pu; C_{p_max} = 0.4288; C_{p_min} = 0.288 α_i,j coefficients of C_p are given in Table 4-7 in [10].