Investigating the effects of grid equivalent circuit at a point of common coupling on bus voltage variations due to variable distributed generation

Increased amounts of distributed generation (DG) in the form of renewable energy resources have presented distribution system operators with unique challenges. A common problem with these types of DGs is that they have a varying output power, which may cause bus voltages to greatly vary. A grid Thévenin equivalent circuit seen from a reference bus can be used to predict changes in bus voltages resulting from DG output changes. A change in the topology of the distribution system would cause a change in its Thévenin equivalent parameters. In this paper, an analytical expression relating bus voltage variations caused by a varying-output DG and the grid Thévenin equivalent circuit is derived. The expression can be used for example to optimally reconfigure the distribution system to minimize the voltage variation impacts from a DG. Simulation results of a 9-bus test system under various system topologies are verify the derived expression.