Direct-Axis Current Orientation-Based Grid Voltage Sensorless Control Strategy for Vienna Rectifier Under Unbalanced and Distorted Grid Conditions

When grid voltage is unbalanced and distorted, the input current harmonics in Vienna rectifier will increase. To solve the issue, a grid voltage sensorless control strategy based on direct-axis current orientation is proposed for Vienna rectifier. In the reference frame, by ensuring that the reference voltage and the input current are in phase, the proposed strategy can avoid the separate operation of positive and negative sequence while reducing the zero-crossing distortion of the input current. The virtual reference voltage is constructed according to the current path and conducting state in the diode rectifier mode, which can reduce the overcurrent during the start-up process. To reduce the harmonics of input current caused by unbalanced grid voltage, the direct axis current control strategy with low-frequency fluctuation is developed in the fundamental plane. In the harmonic plane, the harmonics of the grid voltage are estimated in real time by combining single phase second-order generalized integral, which can suppress the harmonics of the input current under distorted grid voltage. The effectiveness of the proposed strategy is verified on a Vienna rectifier platform.