Limit Cycle Occurrence During Reactive Power Generation by Interlinking Converter in Hybrid Microgrids

This paper is concerned with the analysis of an instability phenomenon, known as limit cycle, in hybrid microgrids (HMGs). The rapid growth of distributed energy resources and their integration into existing distribution networks has opened a new era for electricity generation and distribution markets. The appearance of microgrids, both in the form of ac and dc, is the result of this integration. When both ac and dc microgrids (AC-MGs and DC-MGs) are in the vicinity of each other, they can be interconnected via ac-dc converters, also known as interlinking converters (ICs). Such a structure allows more efficient use of all resources in the system by enabling energy exchange between DC- and AC-MGs. In this paper, it is shown how the reactive power compensation method in IC leads to unstable operation of the HMG. Detailed analysis of this instability reveals that it is caused by a phenomenon known as limit cycle. By knowing the roots of instability, it is possible to eliminate it. Then we studied how the limit cycle that occurred is avoided by nonlinear control techniques support. The analytical studies are backed up by the simulation of a sample HMG.