Effects of virtual resistor in power electronic converter on subsynchronous oscillation damping

Virtual impedance concept provides the impedance effects without need to put real physically impedance in the circuit. In power system, oscillation will not occur as long as the impedance seen by turbine-generator set is 'passive'. In order to ensure the impedance is seen as 'passive' by the turbine-generator set, a series resistor can be placed in the system. This paper proposes implementation of virtual resistor concept in grid connected power electronic converter to replaced the aforementioned series resistor, then analyze its impact on subsynchronous oscillation phenomena. It can be shown that virtual resistor can improve the negative region of converter input admittance. Moreover, it also gives us better damping in system involving grid connected inverter.