Overview
The purpose of the Large Scale System Simulation (LSSS) testbed is to digitally validate the FREEDM System concepts with large and realistic numbers of nodes and resources. The LSSS testbed complements the Hardware in the Loop and GEH testbeds by addressing scalability. The testbed has been used to compare the FREEDM system against traditional energy distribution systems and to benchmark several system-level functionalities, including control strategies, component interactions, fault dynamics, and pilot protection.
The Principal Investigator for this project is Dr. Mariesa Crow.
Method
The inclusion of a high number of power-electronic converters in a traditional AC grid introduces a number of technical issues in control and stability that have not previously been encountered. One area of concern is the potential for instability caused by SST interactions. Researchers validated a proposed SST input filter using the IEEE 34-bus distribution system.
In distribution power systems, feeder voltages can be very sensitive to changes in load and/or distributed generation. FREEDM researchers developed an SST-based, local Volt-VAR Control (VVC) algorithm to eliminate voltage violations even with very high penetration of distributed, intermittent renewable generation. In addition, the algorithm can operate on a subset of SSTs in the system, it does not require any communication between the SST and the substation, and it makes control decisions locally.
A true dynamic (as opposed to quasi-static time series) simulation of thousands of SSTs would be computationally challenging considering the wide range of time scales involved in the different dynamic events. FREEDM researchers therefore developed a differential-algebraic equations (DAE) based simulation involving a hybrid of electromagnetic transient simulation (EMT) and phasor transient stability (TS) simulation. The resulting models were validated using real data for a feeder in Flagstaff, Arizona and using the IEEE 8500 node distribution test feeder.
