Abstract
The main purpose of developing microgrids (MGs) is to facilitate the integration of renewable energy sources (RESs) into the power grid. RESs are normally connected to the grid via power electronic inverters. As various types of RESs are increasingly being connected to the electrical power grid, power systems of the near future will have more inverter-based generators (IBGs) instead of synchronous machines. Since IBGs have significant differences in their characteristics compared to synchronous generators (SGs), particularly concerning their inertia and capability to provide reactive power, their impacts on the system dynamics are different compared to SGs. In particular, system stability analysis will require new approaches. As such, research is currently being conducted on the stability of power systems with the inclusion of IBGs. This review article is intended to be a preface to the Special Issue on Voltage Stability of Microgrids in Power Systems. It presents a comprehensive review of the literature on voltage stability of power systems with a relatively high percentage of IBGs in the generation mix of the system. As the research is developing rapidly in this field, it is understood that by the time that this article is published, and further in the future, there will be many more new developments in this area. Certainly, other articles in this special issue will highlight some other important aspects of the voltage stability of microgrids.
Highlights
Distributed energy resources (DERs) in various forms are rapidly being added to the electrical power grid
To make DERs controllable, they are put in the form of microgrids (MGs), which are defined by the International Council on Large Electrical Systems (CIGRE) as [1]: “Microgrids are electricity distribution systems containing loads and distributed energy resources that can be operated in a controlled, coordinated way either while connected to the main power network or while islanded.”
According to the report by the IEEE PES Task Force on Microgrid Stability Analysis and Modeling [2], though having a generating unit close to the load in an MG helps in the reduction of voltage drop, the limitation on the output current of inverter-based resources (IBRs) is a crucial factor for voltage instability of MGs
Summary
Distributed energy resources (DERs) in various forms are rapidly being added to the electrical power grid. DERs, or with some small difference in meaning, distributed generators (DGs) interfaced to the power grid with power electronic inverters are called inverter-based generators (IBGs), or sometimes more generally are called inverter-based resources (IBRs). The low short-circuit capacity limits its ability in providing the inrush current for induction motors [2,6], and creates a bus with lower strength compared with a similar bus connected to an SG. These characteristics of IBGs cause some significant changes in the system characteristics concerning the power system stability and in particular the voltage stability [7]. Two main approaches can be observed [13]: (a) small-signal stability assessments, and (b) investigating dynamics of the inverters
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