Advanced Control System Design For Large Scale Variable-Speed Variable-Pitch Wind Trubines

Although mass use of fossil energy promotes society economy development, environment of the whole world is polluted. Meanwhile, as fossil energy is increasingly scarce, seeking renewable green energy becomes a consensus among many countries. Recent years witness the fast growth of wind energy as an environmentally friendly energy source, contributing to energy crisis relief and environment pollution reduction.Grid-connected variable-speed variable-pitch wind turbines utilized to convert wind energy have complex structure, normal operation is required in various environmental condition such as turbulent wind, low speed wind and wind gust etc. Grid side proposes highe r requirments for reliable operation of grid-connected wind turbines as well. In order to improve overall running performance and reliability, advanced control technology becomes the core of system design. Large scale wind turbine is nonlinear time varying system with super inertia, whose reference rotor speed tracking control procedure is also restricted by slow responding dynamic of mechanical components. Meanwhile, intermittent time-varying turbulent wind as power source is influented by wind shear effect and tower shadow effect. Present situation is that wind measurement with time lag is inaccurate and unavailable to real-time control, which makes unpredictable sudden wind changes bring strong disturbances to wind energy conversion system. Moreover, problems such as uncertainties resulted by grid connection and outdoor operation also challenge wind energy control system design.In order to obtain steady power output as well as prolong wind turbine lifetime, methodology of keeping generator speed and output power steady is studied firstly in above rated wind speed region. With respect to large inertia of system rotating part, a parallel state predictor of the original plant, whose exact model is not required known is presented with designed poles location to meet ideal dynamic response desire. A novel architecture known as the L1 adaptive controller is designed and implemented for WECS based on a non-affine wind turbine model without a priori knowledge of wind speed measurement and accurate aerodynamic model. The controller has highly structural form for general wind turbines and independence of WECS parameters, which achieves better rated generator speed tracking performance, reduces wind turbines and generator load accordingly and improves power quality.Based on L1 adaptive pitch angle controller, variable pitch variable torque coordinated control is constructed to compensate for regulation shortcoming of individual pitch or torque control input. Variable pitch variable speed wind turbine is a multi-input multi-output strong coupling system. With robustness of system inner uncertainty and external disturbances, sliding mode methology is adopted to realize decoupling control of separate variable torque control inner loop and variable pitch angle control external loop. Therefore, steadier generator speed tracking performance and more stable generated power output is achieved.Considering high wind energy penetration rate scene in power grid, strategies are implemented for two operation conditions in low wind sp eed regine:maximizing wind energy capture and balancing generated output power. Based on indirect rotational speed control, a PI control part with respect to optimal angle speed estimate is added to improve wind energy conversion coefficent. Then the same angle speed reference setting method with traditional indirect rotational speed power regulation is adopted by variable pitch variable torque coordinated regulation stategy. Active sliding mode torque control loop realizes tracking active power reference in order to eliminate error between output power and active power reference, thus more accurate and quicker active power balance between supply and demand is obtained.