Use of Harmonic Power Line Communication to Enhance a Decentralised Control Method of Parallel Inverters in an AC Microgrid

Traditional droop control in AC microgrids relies on telecommunication between a central controller and distributed generators for frequency and voltage restoration. This makes optimal operation of the microgrid vulnerable to a single point of failure i.e. the central controller. Recently, a decentralised control strategy for parallel inverters has been proposed that supplies an AC microgrid load with its demanded current in agreed and equitable fashion, based on local information only and using no telecommunications. In this control strategy the locally measured downstream current is used to derive the current reference for the primary-level control loop in each distributed generator. This facilitates stable operation of the microgrid, with an agreed share of the load current contributed by each inverter. The agreed current sharing distribution is assumed as apriori knowledge, amounting to the assumption that each inverter knows its relative position among the chain of inverters and that all inverters are fully operational. However, in practice, inverter current sharing must be dynamically modified to deal with the loss (or addition) of inverters, and relative changes in their power capabilities. To address this issue, this paper proposes use of a special type of modulator with explicit spectra shaping ability. In the low harmonic pollution environment, which the modulator ensures, it is shown that harmonic power line communication can be utilised for dynamically adjusting the agreed load sharing characteristic.