Distributed Energy Storage Device integration with three phase distribution grid using a Transformerless Intelligent Power Substation

The advent of SiC devices has resulted in the development of 3-phase, Medium Voltage (MV) grid tied Solid State Transformers (SSTs). One such SST is the 100 kVA Transformerless Intelligent Power Substation (TIPS) based on 15 kV SiC IGBTs and 1200 V SiC MOSFETs which interconnects the 13.8 kV distribution grid with the 480 V utility grid. TIPS has an ac-dc-dc-ac multi-module configuration. The availability of 800 V dc and 480 V ac terminals in the system allows for the integration of Distributed Energy Storage Devices (DESDs) with the 13.8 kV MV grid. These DESDs store the energy derived from the renewable sources like solar, wind and wave. The complex nature of the overall system makes the power flow control very challenging during integration. This paper investigates the steady state and transient behavior of the TIPS system when integrated with a battery model representing the DESD. Complete system simulation is carried out using the switching model of the converters along with the dynamic model of the battery and a feeder model similar to IEEE-34 bus system. Experimental verification is done on TIPS prototype at scaled down voltage and power levels.