Co-ordinated voltage regulation in distribution networks with embedded generation

The growing diffusion of Distributed Generation in the MV networks is the result of several concurrent factors. All these factors are changing the way energy is being generated and consumed and the traditionally passive distribution networks are starting to become active by the integration of distributed generation. MV distribution networks are characterised by feeders (aerial or buried) with an almost unitary resistance/reactance ratio which results in relatively high voltage drops and power losses. In the absence of DG, voltage control actions are traditionally performed by the HV/MV substation OLTC transformer, possibly provided by a regulator for line drop compensation, and by shunt compensators suitably located within the network. The uncontrolled power injection throughout the distribution network provided by the DG, even though it may have a beneficial effect in terms of power losses and voltage drop reductions, makes it hard to perform the voltage regulation with the traditional control strategies. Assuming, as it is normally the case, that it is not possible to control and/or limit the active power production of the distributed independent generators, in this work a coordinated voltage/reactive power control scheme is proposed which enables the dispersed generator to participate, together with the HV/MV substation OLTC transformer, to the node voltage regulation of the feeder they are connected to, thus ensuring a better voltage profile along the distribution feeders. The performance of the proposed control scheme has been tested by dynamics simulations on a case study network embedding distributed generation of various nature and size.