Elimination of system induced torque pulsations in doubly fed induction generators via field reconstruction method

Effects of system unbalance and system harmonics on the operation of DFIG are of great concern. This is primarily due to the fact that system unbalance and harmonics can generate unwanted torque undulations that can potentially undermine the mechanical integrity of the tower and reduce the life time of the moving components that are attached to the generator shaft. The present paper focuses on development of a solution for the above problem by judicious selection of the rotor currents to actively eliminate/mitigate these undesirable vibrations. The enabling technology for optimal calculation of the rotor currents is based on the field reconstruction method (FRM). FRM is an analytical tool for approximation of the magnetic field distribution in the middle of the airgap. Once the FRM formulation is set up it is capable to predict the tangential/normal components of the magnetic forces. In the present paper the FRM is applied to compute the rotor phase currents in lieu of the availability of the real time stator currents such that the resultant field will generate a smooth torque.