AC/DC Modular Converter Design In Super UPS System

In order to improve the reliability of the power provided by Uninterruptible Power Supply, Super Uninterruptible Power Supply is proposed. Power conversion system of Super Uninterruptible Power Supply is composed of two standardized converter modules, i.e. AC/DC converter module and DC/DC converter module. The AC/DC converter module is used as the interfaced between DC Bus and AC Energy Source or AC Load. AC/DC converter module can operate as either PWM rectifier or PWM inverter to AC load. Both hardware and software design for AC/DC converter module is investigated so that it satisfies the requirement to these two operating modes with respect to the power quality and conversion efficiency.Firstly, constraints for both modes are investigated and all-purpose filter parameter is decided. Switching device is selected according to the loss breakdown in two modes. Then a shared inner current loop control strategy for two modes is proposed based on which the seamless operating status transition strategy is also provided. Finally, a 100kW prototype is developed to verify the above methods.The unbalance nature for positive dqO control connecting unbalance loads is analyzed through calculating negative sequence output impedance. Thus, negative sequence control is needed. The most commonly used sequence separation method:Delayed Signal Cancellation (DSC) is adopted in this paper. The estimated error for DSC when tracking varying grid frequency is analyzed based on which an improved DSC is proposed. At last, an improved unbalance control strategy is presented and analyzed. The negative sequence output impedance is greatly reduced. The effectiveness of the proposed methods is verified by experiments.