Risk-based dynamic security assessment for power system operation & operational planning

open6noAssessment of dynamic stability in a modern power system (PS) is becoming a stringent requirement both in operational planning and in on-line operation, due to the increasingly complex dynamics of a PS. Further, growing uncertainties in forecast state and in the response to disturbances suggests the adoption of risk-based approaches in Dynamic Security Assessment (DSA). The present paper describes a probabilistic risk-based DSA, which provides instability risk indicators by combining an innovative probabilistic hazard/vulnerability analysis with the assessment of contingency impacts via time domain simulation. The tool implementing the method can be applied to both current and forecast PS states, the latter characterized in terms of renewable and load forecast uncertainties, providing valuable results for operation and operational planning contexts. Some results from a real PS model are discussed.openCiapessoni, Emanuele; Cirio, Diego; Massucco, Stefano*; Morini, Andrea; Pitto, Andrea; Silvestro, FedericoCiapessoni, Emanuele; Cirio, Diego; Massucco, Stefano; Morini, Andrea; Pitto, Andrea; Silvestro, Federic

Anisotropic Strain Limiting

Many materials exhibit a highly nonlinear elastic behavior, such as textiles or finger flesh. An efficient way of enforcing the nonlinearity of these materials is through strain-limiting constraints, which is often the model of choice in computer graphics. Strain-limiting allows to model highly non-linear stiff materials by eliminating degrees of freedom from the computations and by enforcing a set of constraints. However, many nonlinear elastic materials, such as composites, wood or flesh, exhibit anisotropic behaviors, with different material responses depending on the deformation direction. This anisotropic behavior has not been addressed in the past in the context of strain limiting, and naïve approaches, such as applying a different constraint on each component of the principal axes of deformation, produce unrealistic results. In this paper, we enable anisotropic behaviors when using strain-limiting constraints to model nonlinear elastic materials. We compute the limits for each principal axis of deformation through the rotation and hyperbolic projection of the deformation limits defined in the global reference frame. The limits are used to formulate the strain-limiting constraints, which are then seamlessly combined with frictional contact constraints in a standard constrained dynamics solver. Categories and Subject Descriptors (according to ACM CCS): modeling

Demonstration of Converter Control Interactions in MMC-HVDC Systems

Although the control of modular multi-level converters (MMCs) in high-voltage direct-current (HVDC) networks has become a mature subject these days, the potential for adverse interactions between different converter controls remains an under-researched challenge attracting the attention from both academia and industry. Even for point-to-point HVDC links (i.e., simple HVDC systems), converter control interactions may result in the shifting of system operating voltages, increased power losses, and unintended power imbalances at converter stations. To bridge this research gap, the risk of multiple cross-over of control characteristics of MMCs is assessed in this paper through mathematical analysis, computational simulation, and experimental validation. Specifically, the following point-to-point HVDC link configurations are examined: (1) one MMC station equipped with a current versus voltage droop control and the other station equipped with a constant power control; and (2) one MMC station equipped with a power versus voltage droop control and the other station equipped with a constant current control. Design guidelines for droop coefficients are provided to prevent adverse control interactions. A 60-kW MMC test-rig is used to experimentally verify the impact of multiple crossing of control characteristics of the DC system configurations, with results verified through software simulation in MATLAB/Simulink using an open access toolbox. Results show that in operating conditions of 650 V and 50 A (DC voltage and DC current), drifts of 7.7% in the DC voltage and of 10% in the DC current occur due to adverse control interactions under the current versus voltage droop and power control scheme. Similarly, drifts of 7.7% both in the DC voltage and power occur under the power versus voltage droop and current control scheme.This work was supported by the EU FP7 program, through the project “BEyond State of the art Technologies for re-Powering AC corridors and multi-Terminal HVDC Systems” (BEST-PATHS), grant agreement 612748. The simulation toolbox can be downloaded from the project website at www.bestpaths-project.eu (accessed on 10 December 2021)

DC Grids : Motivation, Feasibility and Outstanding Issues : Status Report for the European Commission Deliverable : D5.4

Wind energy is already a mainstay of clean power generation in Europe, with over 100GW of capacity installed so far, and another 120GW anticipated by 2020 according to various analysts. Much of this capacity is expected to be installed offshore, as it is a windier and the source is steadier compared to onshore wind energy. Hence, offshore wind has been envisaged as making a critical contribution to Europe’s demand for electrical energy and to minimising the carbon emissions associated with meeting that demand

On-line dynamic security assessment to mitigate the risk of blackout in the Italian power system

This paper provides a comprehensive survey of the major initiatives and research projects recently carried out by the Italian system operator, Cesi Ricerca, and Universities on power system monitoring, defense, and security assessment. The technological and methodological features of an advanced wide area measurement system (WAMS) are described and the main aspects of an adaptive system for event-based automatic load shedding are presented. Then preventive and corrective security assessment, with particular emphasis to dynamic security assessment-DSA, is introduced. Results from an EU project, where the Italian power system served as a test site for on-line experimentation, are reported. Considering the need for very fast assessment by stability indices, a complementary approach to the above "conventional" DSA, currently under way, is described in further detail. The methodology relies on a correlation model relating significant power system measurements with local loadability margins. Results of some tests on the Italian power system are presented and discussed

Quantification of the Benefits for Power System of Resilience Boosting Measures

Severe natural events leading to wide and intense impacts on power systems are becoming more and more frequent due to climate changes. Operators are urged to set up plans to assess the possible consequences of such events, in view of counteracting them. To this aim, the application of the resilience concept can be beneficial. The paper describes a methodology for power system resilience assessment and enhancement, aimed at quantifying both system resilience indicators evaluated for severe threats, and the benefits to resilience brought by operational and grid hardening measures. The capabilities of the methodology are demonstrated on real study cases

Risk-Based Security and Control Framework for Power System Operation Under Significant Amounts of HVDC-connected Wind Power Generation

In the context of power system operation, probabilistic techniques can provide a deeper insight into security aspects compared to deterministic approaches, by quantitatively considering power system uncertainties and contingency impact. Moreover, they can be helpful to identify and suggest operators the most adequate control actions to reduce the operational risk. This paper proposes an original framework for risk-based assessment and control of operational security in High-Voltage Alternating Current (HVAC) power systems connected to Multi-Terminal High-Voltage Direct Current (MTDC) networks like those envisaged for the integration of future, large off-shore wind farms. After the presentation of a security assessment methodology based on the concept of risk, the paper investigates three possible preventive control strategies to reduce the risk of high current by exploiting control resources available in the system (specifically, generating units and power injections from MTDC grids). Results of the methodology applied to a test system and to a realistic power system (adapted from the Italian transmission network) are presented and discussed

Stochastic modelling of aggregated thermal loads for impact analysis of demand side frequency regulation in the case of Sardinia in 2020

This paper proposes a model of the thermal dynamics and of the end-use of amics and of the end-use of domestic refrigerators (fridges) and water heaters (boilers) in the foretasted scenario of the Sardinian electric network in 2020. This model is employed to evaluate the potential variations of power demand of the aggregates of fridges and boilers during one year in the considered scenario. The resulting quantities can be considered as a form of power reserves to be used for contributing to the frequency regulation through a proper demand side response strategy. The particular case of the system for frequency control proposed by the European Network of Transmission System Operators for Electricity (ENTSO-E) is then analysed by simulations in order to show advantages and drawbacks