Tertiary Control f Tertiary Control ∗ fgc * Concern About the Global MG Optimization * Decentralized Control Level Secondary Control Secondary Control f * Minimize the Average of All Voltage and Frequency Deviations * Centralized or Decentralized ∗+ δf ∗ fCLB f∗ f CLB Nominal Value 0 Feedback Signals P PMG 0 P P1P2 Primary Control * Active and Reactive Power Control * Taking Care of DG Units * Centralized Control ∗ f MG N VCLB N∗ VCLB N N VS1VS2 Secondary V N Compensation 0 IN N∗ N∗ VS1VS2 Primary Droop Control f∗ f CLB P1P2 0 P MG Connection Main Power Grid FIG 4 A schematic diagram of the hierarchical architecture of an MG. DG: distributed generation. Power Quality Power Reliability Economic E ∗ Secondary Control P, Q Reference Values ω∗ P∗ Q∗ MG Network Primary Control Primary Control Tertiary Control MG 1 MG 2 MG N Main Grid P, Q FIG 5 The three control levels of an MG. 22 IEEE POWER ELECTRONICS MAGAZINE z June 2019 Communication Network Primary Control