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The paper  proposes a very simple and attractive algorithm for controlling both active and reactive powers of a DFIM with a unique feedback control loop. In this technical note, it is proved that the presented algorithm in  yields a marginally stable closed-loop system (for the rotor currents). This fact could imply undesired oscillations in the rotor variables, which, eventually, can be large for certain disturbances. The control law in  (which has been cited in more than 100 journal and conference papers) has probably been tested and implemented several times in a real application. However, as the rotor current oscillations are with the same frequency than the power grid (or twice in the three-phase framework), they may have been attributed to the presence of grid-coupling noise or small unbalanced effects instead of the inherent marginal stability of the closed-loop dynamics. The problem detected could be overcome using two nested loops, as many references propose (see a general example in  or a recent application in ), or adopting amore advanced control design technique .