Modeling and control strategy of a single-phase Uninterruptible Power Supply (UPS)

The objective of this work is to get an understandable model of a single-phase Uninterruptible Power Supply (UPS), as well as design and verify the controllers for the UPS. To make the procedure more comprehensive, a basic single-phase UPS is proposed, so it is formed by a battery bank and a bidirectional full-bridge converter (with LC filter and transformer included). The single-phase full-bridge converter is modeled by deducing its transfer functions in two operational modes: voltage-controlled (stand-alone mode, to supply power to the load) and current-controlled (grid-tie mode, to charge the battery). Then, the controllers are designed by using the frequency-analysis approach, so the parameters of PI and PI+ressonant controllers are calculated as examples. External components such as the grid and the load are modeled in a simple way as well. The PSIM software is used to verify and compare the operation of the controllers through simulations, also being able to generate C code to implement the controller into a Digital Signal Processor (DSP). In addition, the models and controller design method can be re-utilized in simulations of other types of UPS and elements of a distributed microgrid.