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Impact of clock drifts on active power sharing and frequency regulation in distributed-averaging secondary control for islanded microgrids

Abstract:

In islanded microgrids (MGs), voltage source inverters (VSIs) can be coupled in parallel to share active power while keeping the frequency at a nominal value. To this end, a hierarchical control framework includes a primary level, commonly based on the droop method, and a secondary level in which several integral policies stand out, among them is the 'distributed-averaging' approach. The latter is a policy inspired by cooperative control techniques that has been applied with satisfactory results. In spite of rich literature in distributed averaging, there is no analysis of the impact of clock drifts on its performance. This paper provides an analysis concerning the effect that local clock-drifts have in the operation of VSIs in islanded MGs when the distributed-averaging policy is implemented in conjunction with the droop method. Specifically, the expressions modeled allow to quantify the steady-state values of frequency and active power when the VSIs are subjected to clock drifts. Select simulations have been developed considering a low-scale MG in order to corroborate the theoretical results which show that the clock drifts favor the occurrence of frequency deviations and power sharing errors. These results show several coincidences with those obtained in analogous analyzes performed with other state-of-the-art secondary control methods.