This example presents a 3-level UPFC (Unified Power Flow Controller). It consists of two 3-level VSI (Voltage Source Inverter) connected to the same DC-link. The right-hand VSI is shunt connected to the AC bus. It works like a STATCOM in order to maintain the voltage on the AC node. The left-hand VSI is series connected to the transmission line. It can insert a regulated seriesl voltage in the transmission line.
Inserting this series voltage in the transmission line gives the possibility to modify the relative impedance of the transmission line, and thus both active and reactive power can be regulated independently.
The AC bus voltage maintain is also a great advantage of the UPFC.
The curves represent a step response of active and reactive power in the transmission line.
It is impressive to observe the high dynamic of the regulation even in such a case of high power UPFC (160 MVA, 6 kV DC, 50 Hz).
The current in the transmission line contains only few harmonics
(THD < 2%).
Once the VSI has been successfully implemented and checked, the studied system may be extended with network elements (machines, transmission lines, transformers, a.s.o) to investigate more in details the behavior of FACTS devices in a high voltage AC network.