Milan Prodanovic

Hydrogen is one of the most promising energy carriers for the future and a key solution for sector coupling. Electrolysers convert electricity into hydrogen for storage and later use, but their deployment depends on improving their economic value, e.g., by scheduling hydrogen production according to electricity prices and renewable resources availability. The value also depends on how the hydrogen is used, e.g., blending it locally in gas-fired units reduces both fuel consumption and emissions. In this context, microgrids (MGs) constitute a key asset, as they aggregate renewable and dispatchable generation, allowing hydrogen production and its use to be coordinated in an optimal way. This paper proposes an optimisation framework for the scheduling of an electrolyser-integrated MG and assesses the value of hydrogen production and blending. The system under study is based on the PrInCE MG at the Polytechnic of Bari, comprising a combined heat and power (CHP) unit, a microturbine, a photovoltaic plant, a battery and an electrolyser. The electrolyser is experimentally characterised in terms of flow rate, efficiency, and losses. The value of hydrogen is assessed from a purely economic perspective, considering electricity prices, hydrogen selling, and green hydrogen incentives. The optimisation results show that blending is profitable only within a narrow electricity price band, and only if low-price periods are present to produce hydrogen at low cost. Furthermore, green hydrogen incentives improve the economic viability of blending. The incentive required to break even, however, becomes very high when prices remain in the mid-to-high range throughout the day. Finally, blending reduces the CO2 emissions of the MG by displacing natural gas, while selling hydrogen yields higher revenues if export infrastructure is available.

Virtual Power Plants (VPPs) represent an aggregation of distributed generators and loads that are capable of following power references sent by grid operators. To guarantee system stability, grid operators need to verify the impact of VPPs on the small-signal stability of electrical transmission systems. Since dynamic models of VPPs have a large number of states, the application of model order reduction (MOR) techniques should be considered for stability analyses. In this paper, the influence of VPPs on the small-signal stability of electrical transmission systems is evaluated. For that purpose, VPPs are modelled in detail, including the dynamics of renewable sources such as wind and solar. Then, the models are reduced by using two MOR techniques, namely state relevance and balanced truncation. The VPPs are connected to the benchmark two-area power system model and their impact on the small-signal stability assessed. The results show that renewable energy-based VPPs have a significant impact on the system eigenvalues and that they provide additional damping to the system. It is shown that the low-frequency dynamic properties can be preserved using low-order reduced models, while higher-order ones are needed for the medium-frequency dynamics. Eigenvalue analysis is used to validate the theoretical developments.

Significant political and economic efforts have been undertaken within the European Union to mitigate the effects of climate change. In alignment with adopted directives, several member states have developed national strategies and prospective studies. One of the most ambitious initiatives is Spain's National Energy and Climate Plan (NECP), which outlines a substantial reduction in CO and other emissions within the energy sector. This talk will address the main challenges associated with the decarbonisation of electricity networks, as well as explore potential technical and market-based solutions. The discussion will begin with an overview of the specific topology of the electricity network in the Iberian Peninsula and its interconnections. This will be followed by an analysis of trends in energy demand and a mapping of renewable energy resources. Finally, the current regulatory framework and the conditions of the energy and service markets will be introduced. Decarbonisation entails the large-scale integration of renewable energy sources (RES) into the power grid. In Spain, this transition primarily involves wind generation in the northwest and photovoltaic (PV) sources in the central and southern regions. Additionally, there are plans for floating offshore wind farms in both the Atlantic and Mediterranean areas. Simultaneously, many conventional coal and gas-fired power plants are being decommissioned. This transformation gives rise to several key challenges: How can RES variability be managed to meet demand? Where should the power grid be reinforced? How can the loss of synchronous generation be compensated? How can service quality be maintained? What market mechanisms and regulatory frameworks are needed? And how should excess generation capacity be handled? To address the loss of synchronous generation-particularly the associated reduction of inertia and voltage stability margins-various technical solutions have been proposed. Power converters used with renewable energy sources and battery systems offer advanced functionalities, such as Grid-Forming capability. Additionally, converters in static compensators, when paired with energy storage, are expected to deliver essential network services. A more traditional alternative involves the deployment of synchronous condensers. The implementation of these solutions is closely linked with the evolution of regulatory frameworks and the development of new service markets. Moreover, advanced planning tools are needed to identify the most cost-effective strategies-whether they are mandated by Grid Codes or capable of competing in emerging service markets. This presentation will explore techno-economic-environmental tools designed to support the transformation of the electricity network in the context of decarbonisation. In particular, it will assess the impact on various aspects of network stability and critically evaluate potential solutions. Different control topologies for power converters will be examined and critically compared, both in terms of their ability to provide grid services and their compliance with evolving Grid Codes.

Virtual synchronous machine (VSM) control is commonly used to control power converters in islanded microgrids (MGs). Frequently, the dynamic model of the MG is unknown and, therefore, the estimation-based, impedance criterion is preferred to design the control parameters. However, the original impedance criterion does not consider the fundamental frequency dynamics and its application may result in technical challenges, such as instabilities, during the connection of new VSMs to already operating MGs. This is relevant for cases where frequency dynamics are critical, as in the case of islanded MGs. In this paper, a methodology to design the parameters of a VSM connected to a MG is presented, based on an extension of the impedance criterion that accounts for the frequency dynamics. It is shown that the proposed method facilitates the understanding of the impact of the VSM parameters on the electromechanical and electromagnetic timescales and on the overall system stability, establishing an intuitive approach for their design. Furthermore, it is shown that the MG frequency dynamics have a relevant effect on the dynamic performance of the VSM, which would not be captured using the conventional impedance criterion. Theoretical developments are verified using simulations and laboratory tests of a representative islanded MG.