Communication-Less Primary and Secondary Control in Inverter-Interfaced AC Microgrid: An Overview

Inverters in microgrids (MGs) face significant challenges during their parallel operations, such as accurate power sharing, deviations in system voltage magnitude and frequency, and imbalance between generation and load demand. To solve these technoeconomic challenges, hierarchical control structures are implemented in MGs. The structure consists of three layers as primary, secondary, and tertiary controls. The control approach can be either communication-based or communication-less at the various layers. The use of communication at primary and secondary layers faces problems, such as communication latency, data drop-up, and expense issues. On the other hand, improved decentralized control techniques being communication-less can avoid the disadvantages of using communication. This article presents an insight into the limitations with the communication-based approach by briefing about the centralized and distributed control techniques at the secondary control layer. Subsequently, the communication-less control techniques and algorithms to achieve accurate power sharing along with the restoration of MG voltage and frequency are described. A comparison among different decentralized droop-based power sharing methods in the primary control layer is done based on review and simulations. In addition, improved communication-less secondary restoration techniques are explained. Finally, future research directions in these areas are listed, aiming to improve the reviewed techniques.