Command Governor Strategies for the Online Management of Reactive Power in Smart Grids with Distributed Generation

High penetration of distributed generation (DG) in medium voltage (MV) power grids may easily lead to abrupt voltage raises in the presence of either low demand conditions or high power production from renewable sources. In order to cope with the possibly occurring voltage limit violation, the active power injected by the distributed generators is typically curtailed, being, however, such an approach suboptimal from an economical point of view and presenting several other disadvantages. To address this issue, the online management and coordination of the reactive power injected/absorbed by the distributed generators acting on the grid are proposed here. The approach is based on command governor ideas that are used here to optimally solve constrained voltage control problems in both centralized and distributed ways. The approach foresees an active coordination between some controllable devices of the grid, e.g., distributed generators and MV/high voltage transformers, in order to maintain relevant system variables within prescribed operative constraints in response to unexpected adverse conditions. Simulation results show that the proposed approach is more effective than approaches suggested by the current Italian norms on DGs connection.