An average model of solid state transformer for dynamic system simulation

The solid state transformer (SST) is one of the key elements proposed in the National Science Foundation (NSF) Generation-III Engineering Research Center (ERC) ldquoFuture Renewable Electric Energy Delivery and Managementrdquo (FREEDM) Systems Center established in 2008. The SST is used to enable active management of distributed renewable energy resources, energy storage devices and loads. In this paper, a 20 kVA solid state transformer based on 6.5 kV IGBT is proposed for interface with 12 kV distribution system voltage. The average model and control scheme of SST including AC/DC rectifier, dual active bridge (DAB) converter and DC/AC inverter are developed to enable dynamic system level simulation. The developed average model is verified by comparing with the detailed switching model simulation. The dynamic system level SST simulation verifies the proposed controller and the corresponding average model illustrates the functionalities and advantages of the SST in FREEDM system.