Abstract: When the grid voltage is unbalanced, even harmonics and odd harmonics will appear on the DC side and AC side of the Vienna rectifier, and the zero-crossing distortion of the current will be aggravated. Therefore, when the grid voltage is unbalanced, this paper establishes the double dq mathematical model of the Vienna rectifier, calculates the angle between the current and the output voltage, analyzes the current zero-crossing distortion of the two control methods based on different control objectives, and proposes modulation method that can minimize the current zero-crossing distortion in the full modulation range is called the vertical foot approximate synthesis method. This method is suitable for both balance and unbalanced power grids. An experimental prototype for Vienna rectifier with a rated power of 4.6kW is built, and the experimental results verify the feasibility and superiority of the method proposed in this paper.