Virtual load damping is a valid alternative to virtual inertia to ensure frequency support in low-inertia power systems. We show that virtual load damping can be provided by multiple small power/capacity inverter-based resources. This can be obtained by exploiting inverter-based resources installed at domestic utilities in distribution feeders, which integrate renewable energy sources. Assessing the impact of these units on frequency requires changing the paradigm used to study power grid stability, since feeders need to be simulated in detail and cannot be represented with equivalent load models anymore, as was done in the past. Time-domain analyses of modified versions of the IEEE 14-BUS and MINIWECC power system benchmarks, obtained by the addition of several feeders in different virtual load damping scenarios, are included to support our claims.

A challenge posed by the increasing penetration of inverter-based resources (IBRs) in distribution networks is how to efficiently simulate a transmission system with a large number of them, since this leads to an "explosion" in system complexity. This paper presents a two-step reduction method for IBR-dominated distribution networks. In the first step, the approach synthesizes a distribution network as a multi-port: one port at the substation connecting it to the transmission system and the others for each IBR connected to the feeder. Then, in the second step, IBRs at the connecting ports are possibly clustered, thus reducing their number. The method differs from others in the literature since it is numerical and can handle clusters of IBRs with different power ratings and set-points. Simulation results of a distribution network with IBRs show the effectiveness of the method.

Some (very) large circuits have the peculiar feature of being composed of numerous repetitions of sub-circuits identical in terms of topology and components. If a traditional simulation paradigm is adopted, such a structure poses a high computational burden. In this paper we describe a general approach based on isomorphism that greatly improves simulation efficiency by exploiting the repetitive structure of these sub-circuits. After describing the core aspects of the approach, we show its potentiality by simulating a battery energy storage system (BESS) at battery cell level in different conditions.

An adequate level of power system inertia and load damping is essential to ensure frequency stability following power imbalances. Prior to that, however, it is first necessary to be capable of estimating these parameters. In this paper, we propose an original method to estimate the global inertia and damping of a power system comprising conventional synchronous generators, as well as modern generation units based on grid forming and following converters, which can provide virtual inertia and load damping. The effectiveness of our approach is tested on a modified version of the IEEE39 power system with ambient noise.

Stability analysis of conventional power systems relies on established modelling practices and tools. Among them, a popular approach exploits the impedances at given buses computed after deriving the power flow solution of the grid typically modelled in the dq-frame. However, in modern grids, this approach is hindered by the presence of elements formulated in the abc-frame, such as inverter-based resources, which make the grid a hybrid system. This paper proposes a novel efficient and versatile tool, directly implemented at simulator level, that allows computing impedances even in these cases.

Modular multilevel converters, used in AC/DC power systems, are characterized by complex (trans-)impedances with a frequency dependence never seen before in electro-mechanical power devices. Since these impedances may severely influence the stability of the entire power system, adequate design actions are needed to ensure safety margins. A straightforward derivation of these complex (trans-)impedances requires making suitable numerical tools available to designers. In this paper, we compute these impedances with the periodic small-signal analysis, a novel numerical approach in the power system realm. After commenting on some impedances computed with this approach, we exploit them to understand how a modular multilevel converter can impact the stability of the AC or DC grids connected to it. Stability issues highlighted through periodic small-signal analysis are verified by detailed transient stability simulations.

Load forecasting plays a crucial role in the day-to-day operations of electric utilities, especially in modern power systems, where a significant share of power generation is attributable to renewable sources. Over the years, several algorithms have been developed to tackle this problem, on time scales ranging from a few hours to several months. Most recent solutions have employed machine learning techniques such as deep learning to increase the granularity of the prediction, down to the single-building level. Here, we employ a framework based on long short-term memory networks to estimate the average power consumption of a single building equipped with solar panels. We show which measurements are more important for an accurate forecast and test several prediction horizons in order to find the best trade-off between training speed and prediction accuracy. Our results reinforce the notion that long short-term memory networks can be successfully used for short-to medium-term load forecasting.

Instability and oscillation issues originating in high-voltage direct current (HVDC) systems comprising modular multilevel converters (MMCs) are gaining increasing interest in the research community. To detect such phenomena in advance, considerable effort has been devoted recently to developing MMC models for small-signal analysis. The derivation of such models is a challenging task due to the topology and complex control structure of MMCs, which results in them having a multi-frequency response. To address this issue, scholars developed methods based on dynamic phasors and harmonic state-space modelling, which, however, require extensive pen-and-paper computations. In this paper, the periodic small-signal analysis (PAC) is adopted to determine numerically several MMCs transfer functions. Such functions can be computed between any electrical circuit node or input/output port, without the need to recast the three-phase average MMC model to derive a linear equivalent one, possibly in the DQ-frame. We show how vector fitting allows converting these functions to equivalent algebraic representations, which can be profitably used to design MMCs and study their stability following some parameter changes. To showcase this feature, we exploit one of these transfer functions to detect DC-side instability in a point-to-point HVDC system.

The dynamics of modern hybrid power systems are characterized by behaviors at different timescales, typically separated by several orders of magnitude. In this paper we apply the envelope-following method to hybrid power systems simulations, in which single-phase and three-phase representations of a power system co-occur. This simulation method is well suited for handling coexisting behaviors occurring at different timescales. Compared to the simulation approaches present in the literature, the envelope-following method does not need to continuously switch between two separate simulation engines, but rather automatically handles instantaneous variations in the dynamics of the system, such as faults or topology changes. Additionally, given the vast penetration of power electronic components in modern electricity networks, employing the envelope-following method allows using a vast array of numerical algorithms that have been developed over the years to simulate electrical and electronic circuits. The proposed approach is validated by means of power systems case studies of increasing complexity.

Modular multilevel converters (mmcs) are the basic building blocks of multi-terminal direct current systems (mtdcs). The current rapid growth of such systems makes it imperative to develop methods to analyse their dc-side stability, thereby ensuring a correct overall operation. In this paper, starting from a simplified mmc model, general conditions for dc-side stability are derived. These conditions have been validated by simulating a point-to-point high voltage direct current system and an mtdc network. mmc models of different degrees of accuracy have been adopted to show that the conditions derived in the paper hold with a good degree of approximation even when more detailed representations are considered.