A control strategy for a distributed generation unit in grid-connected and autonomous modes of operation

This paper presents a new voltage control strategy for an electronically-interfaced distribution generation (DG) unit that utilizes a voltage-sourced converter (VSC) as the interface medium. The control strategy is based on the concept of voltage-controlled VSC (VC-VSC) rather than the conventional current-controlled VSC (CC-VSC). The proposed VC-VSC 1) enables operation of a DG unit in both grid-connected and islanded (autonomous) modes, 2) provides current-limit capability for the VSC during faults, 3) inherently provides an islanding detection method without non-detection zone, 4) provides smooth transition capability between grid-connected and autonomous modes, and 5) can accommodate ride-through capability requirements under a grid-connected mode. This paper also investigates performance of the proposed VC-VSC strategy based on an eigenanalysis in MATLAB, and time-domain simulations in the PSCAD/EMTDC environment. Index Terms--Autonomous operation, distributed generation (DG), islanding detection, ride-through capability, small-signal analysis, voltage-controlled voltage-sourced converter (VC-VSC).