NETWORKED CONTROL AND OPERATION OF CYBER PHYSICAL DC / AC MICROGRIDS

Abstract

Distributed control employing cooperative networks, being the cynosure of research in parallel multi-converter systems, continues to intrigue the intellect and presents ample problem statements to be embarked upon. The centre-flocking and collision avoiding features of animals and birds, natural phenomena like thermodynamic laws, insect swarming, flocking of birds, phase transitions etc. in physical, chemical and biological processes, etc. were studied using consensus algorithms and later correlated to multi-agent systems, communication networks which endow mobility to control decisions via exchange of information among agents in accordance with the designed or inherent communication protocols. These laws were then further extended to microgrids (MGs) realizing its strong potential for the correction of the flaws that arise owing to the line impedances superimposing the effect of droop control using virtual impedances for accurate load current sharing in DC and AC parallel multi-converter systems and to eliminate single-point-of-failure and ameliorate high communication channel bandwidth requirements on account of centralized communication infrastructure. This symbiosis of electrical properties and communication networks commonly known as networked multi-agent systems (MAS) have garnered legit attention owing to their flexibility, scalability and computational efficiency. It also presents the concept of independent, mobile, distributed agents (controllers) that could take decisions of their own by processing information of their nearest agents (controllers). Tracking and synchronization of these agents are the broad classifications in the distributed control theory, wherein it concerns leaderless and leader-follower configurations respectively. The islanded mode of operation of the multiconverter autonomous distribution systems raised concerns over reliable control systems that could accommodate distributed decision-making process. As such a plethora of control techniques for voltage/frequency regulation and load sharing in DC and AC MGs annexed with consensus based distributed control laws have been investigated in literature. Non-linear controllers have also attracted attention as an alternative to the conventional controllers which are designed by obtaining linear models of systems that are inherently non-linear. Nevertheless, this surge in research interest revived the hierarchical control approach to the stand-alone DC/AC systems and rekindled efforts for the improvisation of the functionalities of the disi tributed control layers to a greater extent in order to accommodate and address the loopholes associated with the communication network. Numerous attempts have been made in order to bridge the temporal gap between voltage synchrony and optimal operating points of microgrids by adopting unified control schemes in the secondary layer. These optimizer modules coupled with voltage synchronization protocols aid in achieving energy and cost-efficiency of the standalone topologies in a simultaneous manner.