A 3D-SVPWM Strategy Based on Positive and Negative Bus Voltage Sampling Values for Three-phase Four-wire Three-level Converters

Three-phase four-wire (3P4W) three-level converters can improve the reliability of power supply and is widely used in practical engineering, but when the three-phase load connected is asymmetric, the neutral-point potential of the DC bus will fluctuate. The traditional three-dimensional space vector modulation (3D-SVPWM) builds the space vector diagram and calculates the action time of each vector based on the assumption that the positive and negative bus voltage are equal, which results in a large output error. Therefore, an improved three-level 3D-SVPWM strategy based on actual positive and negative bus voltage is proposed in this paper, which is suitable for the large neutral-point potential fluctuation. Based on the real-time sampling values of positive and negative bus voltage, the three-level three-dimensional space vector diagram is constructed and the action time of each vector is calculated accordingly. This strategy eliminates the error caused by the difference between positive and negative bus voltage, and ensures that the system can still output ideal three-phase voltage waveforms under large neutral-point potential fluctuations. Finally, the proposed strategy is verified through comparative experiments, which can effectively reduce the unbalancing degree and total harmonic distortion (THD) of output voltage, and improve the power quality of independent power supply.