A comparative analysis of SRF-based controllers applied to active power line conditioners

This paper presents a comparative analysis involving four strategies used for extracting the three-phase reference currents for line-interactive Uninterruptible Power Supply (UPS) system, based on the synchronous reference frame (SRF) method. Such strategies can also be used to generate voltages and currents of compensation in other applications for active power line conditioning, such as, series and parallel Active Power Filters (APF), Dynamic Voltage Restorer (DVR), etc. In order to obtain the reference currents, both conventional Butterworth filters and moving-average filters (MAF) were used in the current SRF-based controller. Conventional low-pass filters were implemented in both SRF single-phase strategy (SPS) and improved SRF single-phase strategy (ISPS). The other two strategies were implemented using moving-average filter, such as, SPS-MAF and ISPS-MAF. SRF algorithms have been tested into a three-phase line-interactive UPS system with series and parallel active power line conditioning capabilities, in which the reference currents are used to compensate reactive power and harmonic currents demanded by non-linear loads. Mathematical analyses of the SRF-based controllers are performed and their dynamic responses are discussed. Simulation results were performed to a three-phase four-wire system.