Co-ordinated Voltage Regulation in Distribution Networks with Embedded Generation

The control principle is based on the fact that in radial passive distribution networks, with known load demand and location, the mean network voltage is strictly related to the amount of P and Q flowing through the primary substation transformer. The basic idea is thus to delegate to a centralised controller the task of modulating the reactive power transit through the transformer in order to maintain a desired power factor and thus to contain the level of the transit current required to satisfy the network active load demand. The reactive power regulation is subsequently assigned to the DGs, which are forced by their local regulators to inject power with a given reference cosfi whose value is determined and communicated by the centralised controller (thus actuating a sort of secondary reactive regulation of the MV network). The centralised controller is composed by a Master Regulator (which acts directly on the tap changer of the HV/MV substation transformer in order to maintain a desired power factor) and an array of Secondary Regulators (one for each feeder, which determine the power factor set points to be communicated to the DGs). The performance of the proposed control scheme has been tested on a case study network embedding distributed generation of various nature and size. Simulation results and details on the data exchange needs for performing the co-ordinated voltage regulation will be presented in the paper.