35 research outputs found
How Many Grid-Forming Converters do We Need? A Perspective From Small Signal Stability and Power Grid Strength
Grid-forming (GFM) control has been considered as a promising solution for
accommodating large-scale power electronics converters into modern power grids
thanks to its grid-friendly dynamics, in particular, voltage source behavior on
the AC side. The voltage source behavior of GFM converters can provide voltage
support for the power grid, and therefore enhance the power grid (voltage)
strength. However, grid-following (GFL) converters can also perform constant AC
voltage magnitude control by properly regulating its reactive current, which
may also behave like a voltage source. Currently, it still remains unclear what
are the essential difference between the voltage source behaviors of GFL and
GFM converters, and which type of voltage source behavior can enhance the power
grid strength. In this paper, we will demonstrate that only GFM converters can
provide effective voltage source behavior and enhance the power grid strength
in terms of small signal dynamics. Based on our analysis, we further study the
problem of how to configure GFM converters in the grid and how many GFM
converters we will need. We investigate how the capacity ratio between GFM and
GFL converters affects the equivalent power grid strength and thus the small
signal stability of the system. We give guidelines on how to choose this ratio
to achieve a desired stability margin. We validate our analysis using
high-fidelity simulations
Robust Adaptive Control of STATCOMs to Mitigate Inverter-Based-Resource (IBR)-Induced Oscillations
The interaction among inverter-based resources (IBRs) and power network may
cause small-signal stability issues, especially in low short-circuit grids.
Besides, the integration of static synchronous compensators (STATCOMs) in a
multi-IBR system for voltage support can deteriorate small-signal stability.
However, it is still challenging to understand the impact mechanism of STATCOMs
on IBR-induced oscillation issues and to design STATCOMs' control for damping
these oscillation issues in a multi-IBR system, due to complex system dynamics
and varying operating conditions. To tackle these challenges, this paper
proposes a novel method to reveal how STATCOMs influence IBR-induced
oscillation issues in a multi-IBR system from the viewpoint of grid strength,
which can consider varying operating conditions. Based on this proposed method,
we find critical operating conditions, wherein the system tends to be most
unstable; moreover, we demonstrate that robust small-signal stability issues of
the multi-IBR system with STATCOMs can be simplified as that of multiple
subsystems under critical operating conditions, which avoids traversing all
operating conditions and establishing system's detailed models. On this basis,
an adaptive control-parameter design method is proposed for STATCOMs to ensure
system's robust small-signal stability under varying operating conditions. The
efficacy of proposed methods is validated by a 39-node test system
Damping Low-Frequency Oscillations Through VSC-HVdc Stations Operated as Virtual Synchronous Machines
A Self-Organizing Strategy For Power Flow Control Of Photovoltaic Generators In A Distribution Network
The focus of this paper is to develop a distributed control algorithm that will regulate the power output of multiple photovoltaic generators (PVs) in a distribution network. To this end, the cooperative control methodology from network control theory is used to make a group of PV generators converge and operate at certain (or the same) ratio of available power, which is determined by the status of the distribution network and the PV generators. The proposed control only requires asynchronous information intermittently from neighboring PV generators, making a communication network among the PV units both simple and necessary. The minimum requirement on communication topologies is also prescribed for the proposed control. It is shown that the proposed analysis and design methodology has the advantages that the corresponding communication networks are local, their topology can be time varying, and their bandwidth may be limited. These features enable PV generators to have both self-organizing and adaptive coordination properties even under adverse conditions. The proposed method is simulated using the IEEE standard 34-bus distribution network. © 2011 IEEE
Impacts of Grid Structure on PLL-Synchronization Stability of Converter-Integrated Power Systems
Small-signal instability of grid-connected power converters may arise when the converters use phase-locked loops (PLLs) to synchronize with a weak grid, i.e., operating in grid-following mode. Commonly, this stability problem (referred to as PLL-synchronization stability in this paper) was studied by employing a single-converter system connected to an infinite bus, which, however, omits the impacts of the power grid structure and the interactions among multiple converters. Motivated by this, we investigate how the grid structure affects the PLL-synchronization stability of multi-converter systems. Moreover, we provide guidelines on how to improve the PLL-synchronization stability of multi-converter systems by PLL-retuning, proper placement of converters, or enhancing some weak connections in the network. Finally, we validate our findings with simulation results based on a 39-bus test system. Copyright (C) 2022 The Authors.ISSN:2405-896