Improved digital control scheme of three phase UPS inverter using double control strategy

A novel digital control scheme of a UPS inverter based on the double control strategy is proposed. This method consists of a inner voltage regulated current controller and an outer current regulated voltage controller. In order to improve the dynamic response, the voltage controller has a load predictive feedforward loop and the current controller has an output voltage feedforward loop. PI compensators included in each of the voltage and current controllers are used to guarantee the robustness of the system. The mathematical model and the control algorithm of the proposed scheme are described and digital simulation and experimental results for a 5 kVA prototype are provided to verify the validity of the proposed double control strategy.