A Perturbation and Observation Approach to Decentralized Power Loss Minimization in AC Microgrids

Abstract

This study presents a simple decentralized strategy for power loss minimization in transmission lines in isolated AC microgrids. In this scenario, the proposed approach works as a decentralized secondary control, since the generation units use droop functions as primary controllers (looking at the microgrid from a hierarchical point of view). Therefore, assuming the droop control guarantees the power balance between generation and consumption (as long as the total power demand does not exceed the microgrid generation capacity), the proposed secondary control has the objective of reducing the power loss in the transmission lines. This secondary control adapts the primary control droop functions in order to reach a steady state where the total power loss is minimum. The main advantage of this strategy is the completely autonomous operation of the participating DGs, using only local measurements of system frequency and bus voltages. The distributed adaptation of the droop functions for each of the DGs is carried out by performing a Perturbation and Observation (P&O) algorithm. Initially, for each DG at a time, a small perturbation in the P −f droop function is applied. Then, the produced effects on the system frequency and bus voltage are examined in order to identify if the resultant power balance has reduced or increased the system power loss. This procedure is executed indefinitely by all the participating DGs in the microgrid over a fixed time-step. Eventually, the system reaches a steady state where the power generation of each DG produce the minimum power loss in the transmission lines. The procedure continues endlessly, and any load variation or change in the microgrid topology will lead to a new steady state with different power generation levels for each DG and minimum power loss.