Stability analysis of converter-grid interaction using the converter input admittance

A grid-connected power electronic converter can cause local instabilities when interacting other subsystems-particularly poorly damped resonances-that are electrically nearby. However, oscillations at a certain frequency cannot build up due to the converter if its differential input admittance has positive conductance (real part) at that frequency, since power is then dissipated. Input-admittance expressions for a voltage-source converter are derived in this paper. By adjusting the controller parameters, the admittance can be shaped in order to get positive conductance in desired frequency regions.