Capability Chart for Distributed Reactive Power Resources

The ubiquity of synchronous generation should not be assumed in highly renewable power systems. Various problems may consequently arise, not least of which are the difficulties entailed in maintaining regional reactive power balance. Offering a potential solution to such problems, modern renewable generator technologies offer controllable reactive power resources. As many of these generators will be embedded in distribution networks, their incorporation into transmission system operational and planning activities appears challenging. An extension of the capability chart concept offers insight here: for a given active power exchange between the transmission system and a distribution network section, the range of controllable reactive power typically available is of interest. This aggregate capability depends on the innate machine capabilities of the distributed generators and on the prevailing conditions within the distribution network. Novel optimisation techniques are useful in addressing the latter point, offering a means to identify the combination of power flow profiles within the distribution system most restrictive to reactive power provision. The capability chart thus derived gives the dependable range of reactive power available, under the assumption that each generator is operated to locally maximize its own reactive power contribution. Such a description can be applied in transmission system planning or to quantify the effects of modifications to the distribution system.