As a main control method of distributed generator in a microgrid，PQ control could lead to power oscillations under the circumstance of unbalanced voltage.The relationship between the amplitude of active power oscillations and reactive power oscillations is deduced，and the secondary control of microgrid is further proposed to control active power and reactive power oscillations.An optimization model is built following optimization theory.The model aims at minimizing the amplitude of oscillations，subject to constraints which include the defined power oscillation rate and given values of power reference of PQ control.By using Lagrange multiplier algorithm，the optimization model is transformed into nonlinear equations，thus the optimal current reference of positive sequence and negative sequence could be calculated by solving these nonlinear equations.Dual current control scheme could reduce active power oscillations and reactive power oscillations by current reference.The simulation results show that the proposed secondary control which injects less negative sequence current than traditional control method，can effectively limit oscillations of both active and reactive power.