The utility model relates to a large capacity unified power quality controller. According to the unified power quality controller, the structure that a multi-winding transformer secondary side is connected with an H bridge converter is applied to a UPQC parallel side. Three phases of the parallel side are equivalent to three single-phase rectifier models in bridge joint with online voltage. Due to the fact that each H bridge rectifier is independently controlled, the influence of the unbalance of three phases of voltage can be prevented, and UPQC direct current side voltage is stable when the voltage of a power grid fluctuates. A control method based on virtual orthogonal coordinate conversion is used, so that a single-phase rectification device of the UPQC parallel side is equivalent to a three-phase rectifier model. The controller has the functions of controllable power factor and harmonic suppression of a three-phase rectifier. All functions of the three-phase rectifier can be completely realized under the condition of the voltage of a symmetric system.