Voltage-source converter high-voltage direct current (VSC-HVDC) links offer controllable active and reactive power output, making them a promising asset for emergency voltage support. This paper presents an analytical method for adjusting the active power setpoint of a VSC-HVDC station to maximise loadability during voltage-stressed conditions. By exploiting the geometric structure of converter capability limits, a closed-form expression for the optimal setpoint is derived under combined current and voltage constraints. The method requires local voltage measurements and an estimate of a wide-area voltage angle difference, making it suitable for real-time emergency control without global optimisation. Validation on the Nordic Test System confirms that the analytically predicted optimum is consistent with the setpoint yielding the highest loadability, and that adjustments of active power setpoint can yield a more-than-proportional increase in loadability. The results further indicate robustness to angle estimate uncertainty.

ABSTRACT Voltage instability imposes hard limits on transmission capacity in many power systems, constraining both real‐time operation and ex‐ante capacity allocations. This paper proposes a system integrity protection scheme (SIPS) based on VSC‐HVDC links in hybrid AC/DC power systems, designed to maximise loadability under stressed conditions and thereby increase secure transmission capacity. The core contribution is a novel emergency power control (EPC) strategy, derived in closed form, that considers the active–reactive power trade‐off when converter limits are reached. Two implementations are presented: one based on local measurements alone, and one augmented with synchrophasor data, both targeting the same objective of maximum loadability in the weakened grid. The proposed strategy is validated through dynamic simulations on a two‐node system and a larger benchmark transmission system. Beyond dynamic performance, the scheme is incorporated as a remedial action in the flow‐based (FB) capacity calculation framework, and an improvement to the FB methodology is proposed. Results show that the scheme can increase secure transmission capacity by up to 13%, depending on the initial operating point and proximity to other operational security limits.

The urgent need to address climate change prompts societies worldwide to adopt carbon neutral energy and electrification. To facilitate this, a range of technologies and policies will be needed. Alternatives to traditional power grid reinforcement, such as grid-enhancing technologies and system automation, are particularly attractive due to their potentially low cost and fast deployment time. One alternative is System Integrity Protection Schemes (SIPS) - automatic and curative remedial actions (RAs) which can boost grid transfer capacities without compromising with reliability since they can act faster than manual control. The use of SIPS however is scattered, with limited coordination between countries, and the full potential of using SIPS for capacity enhancement is not yet realized. The aim of this paper is to provide a case study and comparison of SIPS in the Nordic countries, particularly in relation to capacity allocation. It also seeks to harmonize terminology relating to ancillary services, RAs, and SIPS. Finally, it examines and compares the inclusion of RAs and SIPS in different Capacity Calculation Methodologies (CCMs). In both main EU CCMs - Net Transfer Capacity (NTC) and Flow-Based (FB) - RAs play a pronounced role. The paper is based on a survey and interviews with Nordic stakeholders, along with a literature review and analysis of public data. The results indicate a large variation in SIPS use across the Nordics. Regarding terminology, we suggest that SIPS is a subcategory of RAs which overlaps with ancillary services. Concerning CCMs, NTC is unable to fully represent capacity constraints in meshed AC systems, which in turn hinders systematic capacity enhancement using RAs. FB on the other hand explicitly includes RAs in the capacity domain. A lower bound for the economic value of RAs can be calculated, amounting to 11.5 million EUR in the Nordics in Nov and Dec 2024.

To increase the utilisation rate of the power system and accelerate electrification while providing a high degree of security and reliability, System Integrity Protection Schemes (SIPS) are of great importance. SIPS functions are automatic remedial actions, detecting abnormal conditions or contingencies in the system and taking control action to mitigate these conditions. Design, implementation, maintenance and coordination of SIPS are all important aspects for desired operation. However, different actors have chosen different approaches to using SIPS for capacity enhancement, and there are discrepancies in how capacity is valued in relation to for example complexity, reliability and risk. Additionally, definitions often vary between countries. This paper reports on a joint survey and interview study on SIPS with stakeholders and experts in the Nordic countries - including TSOs, DSOs and industry. Combined with a literature review, a comparison and analysis of how SIPS are used in the Nordics is performed, particularly in relation to ENTSO-E capacity allocation.

Power system resilience is an overarching concept covering the whole spectrum of the power system, from design and investment decisions to planning, operations, maintenance and asset management functions. Flexibility concerns the power system's ability to manage changes, with flexibility features able to improve the resilience characteristics of the system, provided that they are integrated into grid planning, in defence plans, and evaluated adequately in the energy market design. An analysis of ongoing worldwide initiatives provides relevant insight into ongoing worldwide initiatives. They provide relevant insight into how flexibility can support resilience, showing the prominence and potential values that can be unlocked, with potentially some low-hanging fruits to start. This paper introduces four innovative concepts: Alternative grid development, system integrity protection schemes, the next level of flexibility and LINK holistic approach to flexibility for resilience as solutions contributing to improving future power systems' resilience.

The energy transition is placing increased strain on power systems and making it challenging for Transmission System Operators (TSOs) to securely operate power systems. System Integrity Protection Schemes (SIPSs) are one of the solutions to address these challenges. SIPSs are a type of over-arching power system control; their goals are to increase the secure utilization of power system assets and to limit the impact of large disturbances on the system. Due to societal developments, the interest in utilizing SIPSs is increasing internationally, highlighting the importance of the standardization of terms and definitions to support collaboration between internationally interconnected power systems. This paper addresses the issue of increasing SIPS literature and the efficient exchange of knowledge about SIPSs by providing a new, up-to-date literature review and proposal for the standardization of SIPS terminology. The need for standardized terminology is highlighted by gathering various terms used to describe SIPSs and proposing a standardization of definitions, terms, and SIPS operational execution steps. The goal of the proposed standardization is to provide clarity and to decrease the sources of misinterpretation in an international collaborative environment. The analyzed literature is further classified according to the SIPS features it addresses, and conclusions about well-established and interesting future research areas are drawn. For example, it has been observed that the most commonly considered SIPS action is load shedding, while more sophisticated actions, e.g., using HVDC (High Voltage Direct Current) and FACTS (Flexible AC Transmission System) installations, controlled together with var rescheduling, are more in the realm of future research that may provide additional benefits to TSOs.

Overvoltage is becoming increasingly prevalent in distribution networks with high penetration of renewable distributed energy sources (DERs). Local control of converter-based resources is a flexible and scalable method to prevent this growing issue. Reactive power is used for voltage control in many local control schemes. However, the typical range of R/X ratios for distribution power lines indicates that mitigation of overvoltage often requires excessive amounts of reactive power. Complete reliance on reactive power thus limits the effectiveness of local control strategies. In this work we instead propose a method that combines enhanced power factor voltage control with upper voltage limit tracking using PI control. We develop a modelling framework and demonstrate the stability of the proposed method. We then simulate the nonlinear operation of two parallel PI controllers in a medium voltage test system.

To collate best praxis and ideas on local electricity markets, this paper surveyed a number of pioneering initiatives in local market design and implementation. The survey focused on the definition of the market itself and the roles and responsibilities of actors within, the distribution of the value of local markets, as well as challenges and current barriers. The results indicate that the main value of a local market is related to the benefits for society as a whole and to a lesser extent individual actors. The main benefits are expected to derive from deferred network investments and reduced network costs. Moreover, local markets are expected to allow for higher shares of clean energy integration and generate positive environmental impacts. Nonetheless, a number of regulatory, economic, stakeholder-related, and other barriers risk obstructing the operation of local markets in the short term and inhibit their adoption in the long run.

Power system flexibility relates to the ability of the power system to manage changes. Solutions providing advances in flexibility are of utmost importance for the future power system. Development ...

In recent years, the impact of natural and man-made hazards on critical infrastructure has resulted in governments, regulators, utilities and other interested parties elevating requirements to enha ...

The focus of the work presented here is to raise awareness of how ancillary services within the NordPool area could be of value in supporting the future grid, and who could be the provider of these services. The ancillary services considered here are not limited to the current market, but also services for future market solutions as well as services for fulfilment of grid codes. The goal is to promote the development of existing and novel solutions to increase the utilisation and thus the value of equipment within the power system. The paper includes a techno-economical categorisation of ancillary services, from a provider's perspective, presenting opportunities and competition. Furthermore, procurers of services could utilise this kind of categorisation to identify possible providers or partners. The analysis of the categorisation shows a broad range of possible providers for each service and a broad range of possible services from each provider.

In this paper, we describe the results from an ongoing project to update the modelling strategies of load models used for planning purposes by the Nordic Transmission System Operators (TSOs) Svensk ...

In this work an overview to the dynamic model of Continental Europe from ENTSO-E, where the main characteristics are summarized and discussed, is introduced. Then, the response of the system to different parameter variations is presented. The objective of the analysis is to identify how the system reacts and evolve on time to fluctuation on standard parameters such as machine saturations, voltage regulator gains, inertia values and loads. Nonlinear dynamic simulations using the professional software DIgSILENT PowerFactory are displayed to compare results.