Impact of double-loop controller on grid connected inverter input admittance using virtual resistor

Grid connected inverter offers better controllability and better operation, however, there is a risk for local instabilities due to particular control scheme. As long as the input admittance is positive at particular resonance frequency, the risk of local instability can be suppressed. In this paper, the virtual resistor concept is employed to obtain the positive input admittance. Impact of double-loop controller using virtual resistor on converter passivity is analyzed by observing the input admittance of the grid connected inverter. By numerical analysis, it can be shown that employment of virtual resistor gives better input admittance of grid connected inverter, particularly in low frequency region.