Performance Analysis of a Speed Sensor-Less Grid Connected DFIG based Wind Energy Conversion System using Nine Switch Converter

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This paper presents the performance study of a Double Fed Induction Generator (DFIG) based Wind Energy Conversion System (WECS) by using the Nine Switch Converter and a new phase locked loop based slip speed estimator is also proposed to obtain speed sensor-less stator field oriented vector control operation. The Nine switch converter having two sets of independent three phase output terminals at two different frequency levels, one set is connected to the rotor winding through slip ring and brushes and other set is connected to the grid through interfacing inductors and a PLL based slip estimator is incorporated with nine switch converter controller for speed sensor-less operation of variable speed wind energy conversion system. The nine switch converter based DFIG system is used for decoupled control of stator active and reactive power exchange between the stator of the DFIG and the grid to ensure maximizing the power generation at unity power factor under varying wind speed and speed sensor-less vector control is incorporated with optimal speed tracking and optimal pitch angle controllers to capture maximum wind energy when wind speed remains within the rated range; and to restrict the captured wind energy to the turbine’s rated level when speed crosses the rated limit to prevent overloading and outage of the wind turbine respectively like convetional back-to-back converter. As compared to conventional back-to-back ac/ac converters, the numbers of power semiconductor switches are reduced in the proposed nine switch converter. The proposed topology has the advantages of reduced cost, more efficient (reduced switching loss) and reduced installation area over back-to-back converter. Simulation has been carried out in MATLAB/Simulink environment and results have been analyzed. Results show that the proposed speed sensor-less DFIG based wind turbine using nine-switch converter can operate at its optimum energy level for a wide range of wind speed and is capable to control active and reactive power independently and reduces the number of switching devices thereby minimizing the cost of the system.