An Unconstrained Voltage Support Scheme for Distributed Generation Connected to Resistive-Inductive Grid Under Unbalanced Conditions

In several countries, during the grid faults, the large distributed generation (DG) is expected to support the voltage at the point of common coupling, as per the prevailing grid code. Large DGs are connected to a high voltage transmission line, where the voltage support is achieved by supplying the reactive power. The recent research trend, however, is toward voltage support by the medium size DGs that are connected to the resistive-inductive grid. The resistive-inductive grid requires both active and reactive power for voltage support. The existing voltage support schemes (VSS) for the resistive-inductive grid impose certain constraints on the proportion of active and reactive components of currents that adversely affect the performance. This article proposes a novel VSS that does not impose such constraints and provides enough compensation when available active power is not sufficient. It also provides the required compensation with much less active power curtailment when available active power is high. That is, the proposed scheme, in both cases, helps in achieving the same voltage compensation in spite of the nature of the injected current being significantly different. This feature is clearly demonstrated graphically using the vector diagram. The reference current expressions for the proposed VSS are analytically derived. The simulation and hardware results demonstrate that the proposed VSS achieves its objectives.