Synchronous reference based harmonic sharing control loops for parallel connected UPS system

Users are favoring of distributed uninterruptible power supply (UPS) systems as an alternative to a large conventional UPS system. To meet expectations of the users, the parallel operation is a special feature of distributed UPS systems. In present work a master-slave based configuration is used for parallel connected UPS systems and the problem associated with power sharing is addressed. The aim is to overcome the challenges of unequal power sharing by using a synchronous reference frame based harmonic sharing control loops. In proposed topology a load current and inverter current information are used by each UPS unit to achieve the required power sharing accuracy. Further, the operations of proposed harmonic sharing loops are compared with the convention control loop. Experimental results from a setup with three parallel 60kVA UPS verify the effectiveness of the proposed harmonic control strategy.