A Coordinated Wind Deloading Estimation Approach for Frequency Control of a Renewable Integrated Grid

Large penetration of DFIG based wind system can have severe impacts on the frequency stability of the grid. Such wind power plant typically injects active power into the network through power electronic converters. Hence they are unable to engage actively in frequency enhancement by providing sufficient inertial or governor support during any unbalance condition. One possible solution can be to keep certain amount of power as deloaded reserve by increasing rotor speed, operating away from maximum power tracking curve. However, restriction on maximum allowable rotor speed can put a limitation on such reserve margin. By controlling the pitch angle, it is possible to maintain the rotor speed within acceptable range. To this end, this study proposes a novel methodology that develops a linear regression based mathematical relationship between deloading percentage and observed frequency response by utilizing a coordinated over speed and pitch angle controller. Through this way, proper deloaded reserve can be allocated to maintain sustainable system frequency. This approach is further analyzed on a modified IEEE 39 bus test grid in DIgSILENT PowerFactory software. Obtained outcomes indicate a linear correlation between lowest frequency point and deloaded reserve for a fixed wind penetration. Nonetheless, minimum required deloading percentage to ensure stable grid operation decreases with the increment in the wind integration percentage. Thus this approach can assist the grid operators to deploy proper wind deloading maintaining uninterrupted operation of the grid.