Stability Analysis of Multiple Grid-Connected Inverters Using Different Feedback Currents

Distributed generation is gaining greater penetration levels in distribution grids due to government incentives for integrating distributed energy resources (DERs) and DER cost reductions. The frequency response of a grid-connected single inverter changes as other inverters are connected in parallel due to the couplings among grid inductance and/or inverter output filters. The selection of the inverter- or grid-side currents as feedback control signals is then not trivial because each one has tradeoffs. This paper analyses the system stability for multiple parallel- and grid-connected inverters using the inverter- or grid-side currents as feedback signals. Modeling of both feedback signals is performed using the current separation technique. Morover, the stability range for different conditions including active damping is analyzed through the root locus technique. The grid-side current has a wider range of stability, but the inverter-side current allows for higher values of the proportional gain near the critical frequency and no extra sensors are needed since measurement of the inverter current is needed for protection in high-power applications.