This paper presents the analyzed results of small-signal stability of a wind-turbine generator based on dynamic-slip induction generator (DSIG) connected to an infinite bus through a step-up transformer and a transmission line. The q-d axis equivalent-circuit model is derived to establish the complete system model under three-phase balanced condition. A lead-lag power oscillation damping controller (PODC) for modulating the rotor's external resistance of the studied wind DSIG is designed by using phase-compensation method to improve the damping of the wind DSIG under different operating conditions. The geometric measure of observability is also employed to select a suitable feedback signal for the designed PODC. A systematic method using a frequency-domain approach based on eigenvalue analysis and a time-domain approach based on nonlinear-model simulations are performed to evaluate the effectiveness of the proposed control scheme and the designed PODC. It can be concluded from the simulation results that the rotor's external resistance joined with the designed PODC is capable of improving damping of the studied wind DSIG under different operating conditions.