Torque ripple compensation using negative sequence current control during unbalanced grid conditions in a DFIG system

A control strategy for the DFIG system during unbalanced voltage conditions is proposed in this paper. If the grid voltage is unbalanced due to grid fault or load unbalance, the voltage contains not only positive sequence voltage but also the negative sequence voltage. A negative sequence current control is implemented in synchronous reference frame to compensate the negative voltage at PCC (point of common coupling). As a result, the voltage of grid connection point, which is the same as the stator voltage, contains reduced amount of negative sequence components and the pulsation of the generator torque is effectively reduced. To investigate the feasibility of the proposed algorithm, both simulation and experimental results are provided using 3 kW hardware-in-loop simulator.