A Generalized Computational Method to Determine Stability of a Multi-inverter Microgrid

Abstract

Abstract-Microgrid-containing parallel-connected inverters, where each inverter is controlled by decentralized active power/voltage frequency and reactive power/voltage magnitude droop control laws results in flexible and expandable systems. These systems have been known to have stability problems for large values of active power/voltage frequency droop control gain. However, so far the stability analysis of multi-inverter systems has always been performed in a computationally intensive manner by considering the entire microgrid. In a practical microgrid, where the number of inverters may be large or the capacity of the units may differ, it becomes essential to develop a method by which stability can be examined without much computational burden. The system of differential algebraic equations has been simplified using justifiable assumptions to result in a final expression that allows the stability of the microgrid to be examined separately with respect to the droop control laws of each inverter transformed into an equivalent network. Moreover, the procedure allows taking into consideration the R/X ratio of the interconnecting cables. Analysis of final expressions validate the stability results reported in literature. Experimental results on hardware show the stable operation of the microgrid.

An Enhanced Dual Droop Control Scheme for Resilient Active Power Sharing Among Paralleled Two-Stage Converters

“…The MG must in turn have other non-renewable sources or storage for balancing supply and demand, which if not catered, will severely limit variation range of the loads. Additionally, the absence of non-renewable sources or storage may introduce a concern, which existing droop schemes have not encountered since they usually assume active power demanded by the droop controller can always be supplied by the sources [23]. This may not be true with RESs because of intermittency caused by climatic and environmental changes.…”

Overview of Technical Challenges, Available Technologies and Ongoing Developments of AC/DC Microgrids

“…Stability issues of high gains of droop controller are also investigated in Ref. [66]. In this chapter, a reduced-order mathematical model of the microgrid is proposed for prediction of stability of microgrids with large number of inverters.…”

“…To address these issues, various strategies have been proposed and developed [63][64][65][66]. In Ref.…”

“…However, interaction between all nodes within a microgrid including both conventional and renewable energy generation sources will not only increase the complexity of the power system considerably, but it will also raise challenging issues of reliability and power quality due to intermitent nature of renewable sources. Therefore, many technical challenges must yet be overcome to ensure safe, secure, reliable, optimized, eicient, and cost efective operation of the microgrid.Academic scholars and industry experts ofered many innovative techniques and technologies to address the challenges of microgrids such as power quality and power low balancing [3][4][5][6][7][8][9][10][11][12], voltage and frequency control , power management [36][37][38][39][40][41][42][43][44][45][46][47][48], optimization [49][50][51][52][53][54][55][56][57][58][59][60][61][62], stability [63][64][65][66], reliability and protection [67][68]…”

Study of large-signal stability of an inverter-based generator using a Lyapunov function

“…Different types of controls, based on the small signal analysis have been proposed on the past to improve the stability of the systems. On [14][15][16] some studies of the root locus analysis were presented while other authors used non lineal techniques such as the method of Lyapunov [17][18].…”