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WIND ENERGY ENERGETICA INDIA New Suzlon operation method “Gust Detection & Reaction” for reducing peak loads The GDR (Gust Detection and Reaction) control feature helps the normal rotor-speed-controller to detect gusts and to react in a way that load peaks and overload speed are reduced as well as shut downs are avoided or at least moderated. Temporarily increased wind speed gradients with or without a strong change of wind directions will be detected as gusts. Development of modern large wind turbines is characterized by the extended efforts taken to optimize the trade-off between maximizing energy yield (profit) and minimizing mechanical loads (cost). The turbine controller mainly influences this trade-off. A lazy controller is able to increase the energy output but cannot react to fast changing wind conditions and induce higher mechanical loads. A fast reacting controller on the other hand can avoid high loads but the electrical energy production is thereby reduced. Especially transient short-time wind speed fluctuations (gusts) lead to the increase of extreme loads as well as fatigue loads. Often the turbine controller reacts after the gust has already gone through the turbine and “overcharged” the rotor. The turbine has not only collected increased mechanical loads but also the rotor is accelerated and can lead to shut-down or to overcompensating of the controller with power-dip as a consequence. So the trade-off is worse, neither of the aims has been achieved. To break through this trade-off, modern controller strategies (e.g. Model Predictive Control (MPC)) are developed. These model-based controllers use additional sensor information, e.g. blade bending, and set optimal pitch angles to avoid peak loads. Other strategies are based on early detection of critical wind conditions. With the help of wind-speed-forecast measurements (e.g. LIDAR) the wind turbine can pre-condition the blade-pitch settings to react in time. A more simple method without expensive additional technology or sensor system is being developed by Suzlon. The GDR (Gust Detection and Reaction) control feature helps Fig 1: Principle of Gust Detection and Reaction (GDR), wind observer uses nacelle based wind speed and wind direction signals to detect gust, as reaction a pitch angle offset will apply. the normal rotor-speed-controller to detect gusts and to react in a way that load peaks and overload speed are reduced as well as shut downs are avoided or at least moderated. Temporarily increased wind speed gradients with or without a strong change of wind directions will be detected as gusts. The wind observer uses the signals of the nacelle based anemometer and the wind vanes. No additional sensor systems are needed. Special signal filtering and an adapting algorithm are included in the GDR wind observer. If a gust is detected the second part of GDR - the reactor - adds in coordination with WTG-controller a defined blade pitch offset as long as the gust has gone through and no new gust was detected. This short time pitch offset reduces the aerodynamic forces of the blades and as a consequence the rotational speed and the blade forces. The reaction time of the rotor-speed-controller will be reduced, as the gust will be detected before the energy of the gust accelerates the rotor too much. If the GDR is able to prevent a hard shutdown, e.g. tripped by rotational over-speed, and the reaction leads to a softer brake program, some of the main local extreme loads will be reduced significantly. Fig 2 shows an example of a detected gust. All in all the GDR helps the WTG to react in time to prevent load peaks and/or shut down. The dilemma of trade-off between high energy generation and lower loads can be solved by energy optimized controller in combination with GDR. After successful finishing of simulation and optimization phase, first trails on WTGs will be done by Suzlon Fig 2: Example of activated GDR in turbulent wind with gust. energetica INDIA · MAR | APR16 57


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