Fault isolation in power electronic based distribution systems without circuit breakers.

摘要

In the Future Renewable Electric Energy Distribution and Management (FREEDM) system, solid state Fault Isolation Devices (FIDs) are used to react to signals from a fault detection and location system to isolate faulted sections of a fault current limited power electronics based 12.47 kV distribution system. They accomplish this by interrupting fault currents, which in the FREEDM system are limited by Solid State Transformers (SST). However, as was expected, due to its silicon transistor technology, the developed FID prototype demonstrated rather high on-state losses during its operation. Therefore, it is necessary to perform comparison studies with alternative methods of sectionalizing faulted parts of the FREEDM grid. To respond to this need, a system study has been undertaken to explore an alternative fault isolation strategy, which instead of allowing fault currents to remain in the system uses the abilities of the SSTs to completely turn off fault currents. Once this turn-off has been accomplished, regular mechanical disconnects isolate the faulted section and the system is reenergized. Behavioral 3-phase PSCAD average-value SST models have been developed and are used in a representative model of the FREEDM Green Hub to demonstrate how this strategy would operate. Simulation data is presented that shows how the SSTs would react to fault situations, remove fault currents, and reenergize the system. The characteristic example system was constructed and parameterized allowing for sensitivity analyses to be performed. A comparison is made with the fault-current-breaking FID method of fault isolation currently in use and it is discussed how the presented approach can be used to evaluate future FREEDM fault isolation strategies.