A novel compact dq-reference frame model for inverter-based microgrids

The development and the experimental validation of a novel dynamic model of an islanded three-phase Inverter-based Microgrid (IMG) is presented in this paper. The proposed model reproduces the relevant system dynamics without excessive complexity and enough accuracy. The dynamics of the IMG are captured with a compact and scalable dynamic model, considering inverter based distributed generators with d-current droop primary and proportional resonant inner controllers. The complete development of the model, the practical assumptions, and the accurate proportional power sharing of the primary control technique are shown. The accuracy performance was verified in experiments performed at the Aalborg Intelligent Microgrids Laboratory for an islanded IMG case

Small signal study of grid-forming converters and impact of different control structures and parameters

Towards transitioning to a carbon-free power system, new dynamic phenomena and interactions involving grid-forming converters (GFMs) will become important as their proliferation occurs to support this transition. The multi-loop control incorporating inner cascaded voltage and current controllers (VC and CC) often utilised within GFMs are generally expected to cause interactions in higher frequency ranges than the (well-studied) dynamics of interest associated with a purely synchronous machine-based system. However, the restricted control bandwidth associated with low switching frequency of large power rated VSCs results in the need for much slower control time constants, causing potentially destabilizing, lower-frequency (or even non-oscillatory) interactions. This paper offers an extensive insight into the small-signal, multi-machine interactions involving large power rated GFMs in a transmission network: the IEEE 39-bus New-England test system (NETS). Furthering the contribution of this paper, multi-loop controllers are employed within the GFMs, offering an insight into their interactions with other power system elements to help aid the ongoing discussions on model appropriateness and direct AC voltage control versus multi-loop control. Finally, parametric sweep sensitivity analyses are performed for the GFMs which are implemented as virtual synchronous machines (VSMs)

Small-Signal Stability Analysis for Droop-Controlled Inverter-based Microgrids with Losses and Filtering

An islanded microgrid supplied by multiple distributed energy resources (DERs) often employs droop-control mechanisms for power sharing. Because microgrids do not include inertial elements, and low pass filtering of noisy measurements introduces lags in control, droop-like controllers may pose significant stability concerns. This paper aims to understand the effects of droop-control on the small-signal stability and transient response of the microgrid. Towards this goal, we present a compendium of results on the small-signal stability of droop-controlled inverter-based microgrids with heterogeneous loads, which distinguishes: (1) lossless vs. lossy networks; (2) droop mechanisms with and without filters, and (3) mesh vs. radial network topologies. Small-signal and transient characteristics are also studied using multiple simulation studies on IEEE test system

Voltage stability of power systems with renewable-energy inverter-based generators: A review

© 2021 by the authors. 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