Control and implementation of converter based ac transmission line emulation

An ultra-wide-area transmission network emulator, also called hardware test-bed (HTB), is being developed to emulate the large-scale interconnected power systems by using regenerative converters. Ac transmission line emulator is a key component in this system to connect two-area grid and to study the ac system's behavior under different scenarios. In this paper, two generic approaches of emulating the ac transmission line are developed based on back-to-back (BTB) voltage source converters (VSC), corresponding to the phasor domain model and discrete time domain model respectively. Two control schemes are presented, both showing less dependency on the communication speed and digital delay, thus enabling high accuracy and the possibility to emulate the dynamics of ac line flow. The impacts of BTB converter losses on the emulation performance are also analyzed, and the corresponding solution is provided. Finally, simulation and experimental results obtained from a scale-down three-phase prototype well verify the modeling and control scheme of the ac line emulation under normal operation and tripping line scenarios.