Power quality improvement using a dual unified power quality conditioner/uninterruptible power supply in three-phase four-wire systems

Using a dual compensation strategy, this study proposes the analysis and implementation of active power quality conditioners (PQCs), which are applied for power quality improvement in three-phase four-wire (3P4W) systems. By means of similar control strategy use, the topology employed to implement the PQCs can operate as unified PQC (UPQC), or, through some circuit modifications, as uninterruptible power supply (UPS) system. Considering 3P4W systems, the use of the dual compensation strategy into the PQCs comprised of two four-leg (4-Leg) converters is the main contribution of this study. Different from the conventional strategies, in the dual compensation strategy, the 4-Leg converter connected in parallel with the load is controlled to operate as a sinusoidal voltage source, whereas the 4-Leg converter connected in series between the grid and the load is controlled to operate as a sinusoidal current source. Both the voltage and current controllers are implemented into the synchronous rotating reference frame, and the converters use the three-dimensional space vector modulation technique. Experimental tests, based on a digital signal processor, are performed in order to validate the theoretical development and to verify both static and dynamic performance of the PQC operating as UPQC, as well as UPS system.