Design and Demonstration of A GRID-Connected Modular All-SiC Transformerless Energy Router (GRID-MASTER) (22-01)

Principal Investigator: Dr. Yue Zhao

Over the past decade, the medium voltage (MV) solid state transformers (SST) have been
extensively studied and demonstrated as an enabling technology to replace the bulky line
frequency transformer and provide advanced grid supporting functionalities. To connect to the
MV AC grid, most of the proposed solutions utilize series connected modular converters on the
AC side. Several MV SSTs, both Silicon based and Silicon Carbide (SiC) based systems, have been
developed and reported in the public domain. However, the major issues of these system are the
low efficiency, e.g., less than 98%, and high volume due to the use of multi-stage architecture
and the bulky DC link capacitors. Therefore, as stated in the Needs Document D1.1 developing
MV SSTs that are highly efficient, low volume, is still desirable. Architecture studies of how these
applications apply and impact the grid are still needed.

Through a program funded by the Department of Energy (DOE), a highly efficient high-density
modular SST concept has been developed, from the base unit, i.e., Power Cell, which is an aircooled
isolated DC/AC conversion unit rated at 75 kVA, to the Power Stack, which consists of 3×
Power Cells. Then with several Power Stacks, a MV Tower can be developed. Two all SiC full-scale
Power Stack prototypes have been developed and tested to reach full power 450 kVA with up to
4160V AC output. Due to the use of SiC, the power density and efficiency of the Power Cell are
much higher than that of the state-of-the-art. However, similar to other SST systems, the
controller architecture is custom designed for a particular application. If the system is rewired
into a different configuration, the control algorithms and even controller hardware may need to
be modified, which reduces the system flexibility. In this project two major challenges will be
addressed, i.e., (1) how to develop a modular controller hardware architecture to freely scale up
in terms of the power and/or voltage; and (2) what is the most practical control software
architecture to enable the flexible inter-connection among Power Cells and/or Stacks. To address
these challenges, which also aligns with the Need D1.1 and M1.3, in this project, a GRIDConnected
Modular All-SiC Transformerless Energy Router (GRID-MASTER) will be developed
and demonstration. This goal will be achieved through a couple of innovations in the architecture
studies, especially from the controller hardware and software perspectives.


Posted on

January 1, 2022

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