Generalized multivariable small-signal model of three-phase grid-connected inverter in DQ-domain

This paper proposes a multivariable small-signal model of a three-phase grid-connected renewable energy inverter in dq-domain. The model allows predicting the shape of inverter output admittance with an arbitrary power factor and includes the dynamic effects of DC-voltage control, AC-current control, phase-locked-loop and decoupling terms. There is no need to simplify the model by neglecting any cross-couplings between d and q-components because the model is developed by recognizing the multiple-input multiple-output (MIMO) nature of the inverter. The output admittance matrix of the inverter including the crosscoupling admittances can be accurately predicted which allows precise evaluation of small-signal stability with finite grid impedance. It is shown that neglecting the crosscoupling admittances gives inaccurate predictions on small-signal stability and the full admittance matrix should be used in stability analysis instead.