The popularity of power electronic applications in the power grid, making the system stability issues aroused widespread concern. The virtual synchronous machine makes it possible to control the stability of the system by simulating the damping and inertia characteristics of the motor. Load as a major player in the grid should also bear the corresponding responsibility. In this paper, we take the load side of the virtual synchronous machine (synchronous rectifier) as the research object. Aiming at the three-phase unbalance problem in distribution network, the control strategy is improved by power analysis to achieve the purpose of stabilizing the DC load voltage. The simulation model of Matlab/Simulink under power fluctuations and unbalanced three-phase conditions is obtained. Simulation results prove the accuracy and effectiveness of the method.