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This paper proposes a strategy for hybrid control of variable speed wind turbines connected to the electrical grid, using a Double Fed Induction Generator (DFIG). An efficient validation approach is presented in three steps. The first step concerns the comparison of performances between Fuzzy Logic (FL), H infinity (H∞) and Integral Proportional action (PI) controllers. In a system context based on the DFIG direct vector control structure, the strengths of H∞are reinforced in the second step by implementing two new advanced mixed controllers, namely the FL-H∞and the combination of the PI, the Proportional Integral Derivative (PID) action, the Filter Derivative (Fd) action and the H∞(PI&PID-Fd)-H∞. The second step, based on a simplified system of indirect vector control structure of the DFIG, allows the performance of the (PI&PID-Fd)-H∞to be compared with that of the FL-H∞. In contrast to the latter, it emerges that, in addition to its simplicity of implementation and the reduction in calculation and simulation time, the (PI&PID-Fd)-H∞is very reassuring in terms of robustness against mixed uncertainties, stability, precision, tracking and decoupling between active (PS) and reactive (QS)power. This makes (PI&PID-Fd)-H∞a very advantageous choice for the design of the proposed hybrid control system. The final step gives a more real-life picture of hybrid control of the wind system as follows, a random wind model is considered, an FL regulates the Maximum Power Point Tracking (MPPT) of the turbine model, the PI-H∞and (PID-Fd)-H∞control the Ps and Qs on the nominal DFIG model via a Rotor Side Converter (RSC), an FL regulates the DC-BUS voltage and the H∞control the currents via a Grid Side Converter (GSC) and filter. According to the results, and in contrast to a conventional PI control system, the hybrid control system offered has very good performance, particularly with regard to, for example, optimal extraction of energy from the wind, the currents fed into the grid are well balanced, the Total Harmonic Distortion (THD) is reduced and the cos ϕ is almost equal to unity. In addition, a good compromise between stability and expected performance is ensured. Consequently, the proposed strategy has reasonable and very favourable advantages for the optimisation of energy conversion in grid-connected wind energy systems. The results are developed in the MATLAB/Simulink environment. |
