The drive towards fully decarbonized power systems leads to the widespread replacement of synchronous generators by inverter based resources (IBRs). IBR installations bring new dynamics to the power systems and affect them in various ways when connected to different locations in the system. The use of short-circuit ratio (SCR) for assessing system strength appears inadequate, especially against small-signal stability such as sub/supersynchronous oscillations that are caused by interactions between IBR. This paper presents a new metric, namely Admittance Margin (AM), that indicates the maximum allowed change in the admittance observed at a bus for a mode of interest, where for changes less than the maximum, the mode will remain stable. AM is proposed as a companion to the recently proposed small-signal system strength metric, impedance margin ratio (IMR), and is tailored for use to assess small-signal system strength at buses which do not yet have equipment connected but where a resource development is planned. It can identify weak buses in the system, and guide accordingly the installations and placement of future IBR in the system. It is shown that introducing grid-following (GFL) inverters at buses with low AM should be avoided as it significantly destabilises the system, while on the other hand, introducing grid-forming (GFM) inverters at buses with low AM could significantly damp specific oscillatory modes. The usefulness of the AM metric is validated on a modified IEEE 14-Bus test system that contains multiple IBRs.

Inverter-based resources (IBRs) possess dynamics that are significantly different from those of synchronous-generator-based sources and as IBR penetrations grow the dynamics of power systems are changing. This article discusses the characteristics of the new dynamics and examines how they can be accommodated into the long-standing categorizations of power system stability in terms of angle, frequency, and voltage stability. It is argued that inverters are causing the frequency range over which angle, frequency, and voltage dynamics act to extend such that the previously partitioned categories are now coupled and further coupled to new electromagnetic modes. While grid-forming (GFM) inverters share many characteristics with generators, grid-following (GFL) inverters are different. This is explored in terms of similarities and differences in synchronization, inertia, and voltage control. The concept of duality is used to unify the synchronization principles of GFM and GFL inverters and, thus, established the generalized angle dynamics. This enables the analytical study of GFM-GFL interaction, which is particularly important to guide the placement of GFM apparatuses and is even more important if GFM inverters are allowed to fall back to the GFL mode during faults to avoid oversizing to support short-term overload. Both GFL and GFM inverters contribute to voltage strength but with marked differences, which implies new features of voltage stability. Several directions for further research are identified, including: 1) extensions of nonlinear stability analysis to accommodate new inverter behaviors with cross-coupled time frames; 2) establishment of spatial–temporal indices of system strength and stability margin to guide the provision of new stability services; and 3) data-driven approaches to combat increased system complexity and confidentiality of inverter models.

Since its inception, the smart grid concept has revolutionized power systems worldwide. Concurrently, the energy industry has witnessed significant changes, such as the clean energy transition, digitalization, and the artificial intelligence (AI) revolution. These changes have profoundly impacted power systems technology and energy consumers. As such, power and energy systems have evolved into a multidisciplinary research area encompassing power engineering, information and communication technologies (ICTs), computer and data science, control and optimization theory, and social sciences. In this context, power systems worldwide have moved beyond the smart grid, transforming in terms of technology, physical tructure, and business model. Therefore, this proceeding aims to summarize current developments, recognize new trends, and collect experiences worldwide, focusing on distribution system digitalization and marketization, renewable energy penetration, and electronic device integration.

The large-scale integration of converter-interfaced resources in electrical power systems raises new threats to stability which call for a new theoretical framework for modelling and analysis. In this paper, we present the intrinsic analogy of a power system to a communication system, which is here called power-communication isomorphism. Based on this isomorphism, we revisit power system stability from a communication perspective and thereby establish a theory that unifies the heterogeneous power apparatuses of power systems and provides a bridge between electromagnetic transient (EMT) and phasor dynamics. This theory yields several new insights into power system stability and new possibilities for stabilization. In particular, we demonstrate that a system of 100% converter-interfaced resources can achieve stable synchronization in small- and large-signal sense under grid-following control which was commonly considered impossible.

This paper presents a problem in power networks that creates an exciting and yet challenging real-world scenario for application of multi-agent reinforcement learning (MARL). The emerging trend of decarbonisation is placing excessive stress on power distribution networks. Active voltage control is seen as a promising solution to relieve power congestion and improve voltage quality without extra hardware investment, taking advantage of the controllable apparatuses in the network, such as roof-top photovoltaics (PVs) and static var compensators (SVCs). These controllable apparatuses appear in a vast number and are distributed in a wide geographic area, making MARL a natural candidate. This paper formulates the active voltage control problem in the framework of Dec-POMDP and establishes an open-source environment. It aims to bridge the gap between the power community and the MARL community and be a drive force towards real-world applications of MARL algorithms. Finally, we analyse the special characteristics of the active voltage control problems that cause challenges (e.g. interpretability) for state-of-the-art MARL approaches, and summarise the potential directions.

Power electronics based dc transformer is the key equipment for MVDC distribution network interconnection, which requires both high step-ratio and low step-ratio dc-dc conversions to interface dc links at different voltages. This paper reviews the original high step-ratio resonant modular multilevel dc converter (RMMC) for MVDC applications and then presents a step-by-step circuit evolution which drives the high step-ratio RMMC to a low step-ratio RMMC, which inherits all the key operational advantages that were present in high step-ratio RMMC version including soft-switching operation, inherent balancing and high effective switching frequency. Furthermore, based on these two basic RMMCs, a derivative family of RMMCs for both high step-ratio and low step-ratio conversion is provided for different kinds of interconnection requirements in MVDC distribution system. The theoretical analysis for both high step-ratio and low step-ratio RMMCs are verified by a set of medium voltage full-scale simulation examples.

In an autonomous microgrid without connection to the interconnected grid to support the frequency and voltage, it is more complex to control and manage. Thus in order to investigate the dynamic stability of the medium-voltage (MV) microgrid in Dongao Island, a detailed small-signal state-space model of the autonomous MV mixed-source microgrid containing diesel generator set (DGS), grid-supporting battery energy storage system (BESS), squirrel cage induction generator (SCIG) wind turbine and network is developed. Sensitivity analysis is carried out to reveal the dynamic stability margin of the MV microgrid and identify the permissible variations range of the droop coefficients. Finally, the theoretical analysis is verified with time-domain simulation and experimental results.

Power distribution networks with distributed generators (DGs) can exhibit complex operational regimes which makes conventional management approaches no longer adequate. This paper looks into key communication infrastructure design aspects, and analyzes two representative evolution cases of Active Network Management (ANM) for distributed control. Relevant standard initiatives, communication protocols and technologies are introduced and underlying engineering challenges are highlighted. By analyzing two representative case networks (meshed and radial topologies) at different voltage levels (33 and 11 kV), this paper discusses the design considerations and presents performance results based on numerical simulations. This study focuses on the key role of the telecommunications provision when upgrading and deploying distributed control solutions, as part of future ANM systems.

Energy harvesting generators are attractive as inexhaustible replacements for batteries in low-power wireless electronic devices and have received increasing research interest in recent years. Ambient motion is one of the main sources of energy for harvesting, and a wide range of motion-powered energy harvesters have been proposed or demonstrated, particularly at the microscale. This paper reviews the principles and state-of-art in motion-driven miniature energy harvesters and discusses trends, suitable applications, and possible future developments.