Search

In recent years, High Voltage Direct Current (HVDC) transmission has become a technically and economically feasible technology, to the point that HVDC networks integrated with AC systems are being developed. However, only a few research works address Transmission Network Expansion Planning (TNEP) considering both AC and DC networks. To develop an AC/DC TNEP approach, precise models that describe the behavior of the transmission lines and their associated converter stations in DC are required. This article proposes a formulation based on a non-convex model and a heuristic optimization method to solve the AC/DC TNEP. The implementation is based on Julia using the Garver AC/DC 6-bus, the IEEE 14-bus AC/DC, and IEEE AC 24-bus test systems.

A prerequisite to dynamic state estimation of a stochastic nonlinear dynamic model of a power system is its observability analysis. However, due to the model nonlinearity, the traditional methods either suffer from a poor estimation accuracy if a linear approximation is performed or yield an extremely complicated procedure if the Lie-derivative method is applied to a large-scale power system. To address these weaknesses, we propose a new data-driven Koopman-based observability method by revealing the link that exists between the Koopman operator and the Lie-derivative in the Koopman canonical coordinates. This enables the proposed data-driven method not only to be fully derivative-free, which alleviates its implementation complexity but also overcomes the model nonlinearity and inaccuracy of the system. Furthermore, as an important byproduct, the proposed observability analysis scheme provides a valuable guide for the selection of the observables of the Koopman operator, which is a major difficulty for the application of this operator. Finally, we demonstrate the excellent performance of the proposed method on several IEEE standard test systems.

To improve the capacity of the power system damping, a power system stabilizers (PSSs) is typically the chosen option. Traditional PSSs performance fails to provide superior damping under other operating circumstances. Many adaptive control approaches have been proposed to solve this problem, but they are both difficult and expensive. Implementing a PSSs damping controller requires extensive system modeling, placing a heavy computational burden on the system, and is a time-consuming process. A Neuro-Fuzzy Controller (NFC), a damping controller that can take the place of the FFA-PSS controller, was proposed to address these shortcomings. The dynamic model of 10-machine test systems under multiple operating conditions was developed with the presence of NFC in SIMULINK. After carrying out the time-domain simulation on the New England IEEE test system, the proposed NFC model produced a 13% rotor speed and 43% rotor angle respective angle stability enhancement in G5 based on the time to settle when compared to the FFA-PSS model. Our work has led us to conclude that the simulation results with the proposed NFC model shows that the Electromechanical Modes (EMs) eigenvalues were shifted to the left in S-plane and the system damping was greatly enhanced.

To improve the capacity of the power system damping, a power system stabilizers (PSSs) is typically the chosen option. Traditional PSSs performance fails to provide superior damping under other operating circumstances. Many adaptive control approaches have been proposed to solve this problem, but they are both difficult and expensive. Implementing a PSSs damping controller requires extensive system modeling, placing a heavy computational burden on the system, and is a time-consuming process. A Neuro-Fuzzy Controller (NFC), a damping controller that can take the place of the FFA-PSS controller, was proposed to address these shortcomings. The dynamic model of 10-machine test systems under multiple operating conditions was developed with the presence of NFC in SIMULINK. After carrying out the time-domain simulation on the New England IEEE test system, the proposed NFC model produced a 13% rotor speed and 43% rotor angle respective angle stability enhancement in G5 based on the time to settle when compared to the FFA-PSS model. Our work has led us to conclude that the simulation results with the proposed NFC model shows that the Electromechanical Modes (EMs) eigenvalues were shifted to the left in S-plane and the system damping was greatly enhanced.

Power electronic converter (PEC) is a key element for the successful integration of novel technologies, PEC working as inverter at novel generation technologies are the decisive components to zero-net carbon emissions in the electricity systems. The colossal penetration of IBG tends to produce several issues in the power networks. There is a tendency to agree that the voltage source converters (VSCs) empowered with the so-called grid forming (GFR) control may provide a long-term solution for the inverter-based generation-dominated power systems. This scientific paper presents an investigation (based on numerical simulations) of the effect of the virtual impedance control mode of one grid forming control technique in the power swing of power systems. Numerical time-domain simulations on test systems are used to assess the effect of the virtual impedance (VI) control mode of the synchronverter (SynC) during a power swing. In both cases, the simulation-based investigation has shown evidence of using high and low virtual impedance in both cases, considering constant impedance and proportional over-current limitation. However, this paper concludes that further assessments are required., Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public., Intelligent Electrical Power Grids

In a previous work, we have shown that miniaturized test systems can be used to reproduce the energy yield of larger systems accurately. Accordingly, such miniaturized systems can be used to evaluate varying system concepts or to reveal differing properties in direct, comparative measurements. The smaller size enables a considerably increased flexibility and a fast realization compared to full sized test fields. Based on such measurements, optimized system configurations can be found or a yield prediction can be made. This is of interest for PV systems and technologies for which simulation tools with sufficient or validated accuracy are not available. Examples are bifacial modules, particularly with steep tilt angles or Perovskite cell types. In this paper, we report on a commercially available miniaturized model kit to reproduce measurements of PV systems. It is an improved version of the previously used test rig that allows a flexible arrangement of the modules to represent various types of PV systems.

The fifth generation (5G) mobile communication system will change the world through intelligent mobile devices and flexible networks to offer a new wide range of applications. mmWave radio propagation combined with a variety of new frequencies and bandwidth creates new radio measurement challenges. There are major limitations when it comes to mmWave components and measuring instruments. In this work we have designed and built a 7-GHz measuring system intended for in-situ channel characterization in environments where transmitters and receivers are located at different heights, like e.g. wireless sensor network installations. Such configurations are likely to be commonplace with the advent of e.g. Industry 4.0. The system has been tested in space experiments, where the distance and height between transmitter and receiver were changed. In addition, wave propagation behavior was studied through different materials placed between transmitter and receiver. The measurement system presented in this paper will provide an insight into the design of similar 5G test systems.

In a previous work, we have shown that miniaturized test systems can be used to reproduce the energy yield of larger systems accurately. Accordingly, such miniaturized systems can be used to evaluate varying system concepts or to reveal differing properties in direct, comparative measurements. The smaller size enables a considerably increased flexibility and a fast realization compared to full sized test fields. Based on such measurements, optimized system configurations can be found or a yield prediction can be made. This is of interest for PV systems and technologies for which simulation tools with sufficient or validated accuracy are not available. Examples are bifacial modules, particularly with steep tilt angles or Perovskite cell types. In this paper, we report on a commercially available miniaturized model kit to reproduce measurements of PV systems. It is an improved version of the previously used test rig that allows a flexible arrangement of the modules to represent various types of PV systems.

A modern power system is characterized by a stochastic variation of the loads and an increasing penetration of renewable energy generation, which results in large uncertainties in its states. These uncertainties bring formidable challenges to the power system planning and operation process. To address these challenges, we propose a cost-effective, iterative response-surface-based approach for the chance-constrained AC optimal power-flow problem that aims to ensure the secure operation of the power systems considering dependent uncertainties. Starting from a stochastic-sampling-based framework, we first utilize the copula theory to simulate the dependence among multivariate uncertain inputs. Then, to reduce the prohibitive computational time required in the traditional Monte-Carlo method, we propose, instead of using the original complicated power-system model, to rely on a polynomial-chaos-based response surface. This response surface allows us to efficiently evaluate the time-consuming power-system model at arbitrary distributed sampled values with a negligible computational cost. This further enables us to efficiently conduct an online stochastic testing for the system states that not only screens out the statistical active constraints, but also assists in a better design of the tightened bounds without using any Gaussian or symmetric assumption. Finally, an iterative procedure is executed to fine-tune the optimal solution that better satisfies a predefined probability. The simulations conducted in multiple test systems demonstrate the excellent performance of the proposed method.

© 2019 IEEE. Modern grid codes demand the integration of voltage support capability with photo-voltaic (PV) generators to ensure a secure and reliable grid operation. On the other hand, short-term voltage instability (STVI) of distribution networks (DNs) is one of the key issues to be addressed due to the rising proportion of induction motor (IM) loads. However, the literature lacks an extensive analysis of short-term voltage stability (STVS) following an unsymmetrical fault in a DN, as well as an effective voltage-support strategy for PV units to improve the STVS while mitigating the excessive voltage swell. Therefore, at first, this paper thoroughly investigates the STVS of a DN subjected to an unbalanced fault. It is perceived that voltage support through conventional methods can increase the risk of STVI and excessive voltage swell. Secondly, a new voltage-support strategy is proposed based on the negative sequence voltage at the point of common coupling (PCC) to improve the STVS and to limit the voltage swell within requirement. The key features of the proposed method are (1) fast and accurate estimation of a network's impedance at PCC is not required, and (2) can be re-designed considering the network behaviors. The proposed method is validated on two IEEE benchmark test systems, and the provided results designate the effectiveness in improving the STVS and alleviating over voltage issues in a DN.

Unit Commitment (UC) is a computationally intensive problem, which has been solved sufficiently well for day ahead scheduling and single scenario simulations. However, the introduction of renewable energy sources and storage exposes new challenges in computation time due to the need for large-scale multi-scenario modeling while preserving inter-temporal constraints. To address this, we introduce a novel approach with adaptive time resolution that increases simulation speed and preserves accuracy. We reduce the size of the problem by grouping successive time intervals with similar net demand levels, forming a new longer interval. In comparison with the conventional UC solutions, the proposed approach is computationally more efficient, as it avoids repeated optimization for similar intervals. We analyze the quality of the solutions using the 6-bus, and IEEE 118-bus test systems as the two case-studies. The numerical results demonstrate that high quality solutions can be obtained with significant gains in computational speed, especially for the more difficult IEEE 118-bus case which is 115 times faster with a maximum error of less than ±1%.

A method for superimposing voltage sources is sought optimized by using a sparse triangular solver and multiprocessing. A revision to the method is suggested which exploits Schur’s complement of the network admittance matrix and optimal re-use of computations. The algorithm is implemented and parallelized for shared memory multiprocessing. The proposed algorithm is tested on a collection of large test systems and performance is found to be significantly better than the reference method. The algorithm will thereby facilitate a speed-up of methods relying on Thévenin equivalent representation such as the Thévenin equivalent method for contingency assessment.

This paper identifies weakness of existing method for voltage stability assessment and proposes new approach for determining point of maximum deliverable power to a given load that accounts for the variations in the Thevenin voltage magnitude. The approach uses Thevenin equivalents seen from nodes of constant voltage magnitude and load nodes in order to determine a distance to instability. A simple five-bus system together with IEEE 14 bus system were used in order to perform dynamic simulation in PSS/E. The simulation data were used to create synthetic Phasor Measurement Unit (PMU) snapshots, which served as input to the proposed approach. The new approach is demonstrated on the two test systems, where improved accuracy in determining the point of maximum deliverable power is demonstrated. The results show that the point of maximum deliverable power to the load occurs well before the Thevenin impedance matching criteria.

This paper presents an improved way of applying Monte Carlo simulation using the Cross-Entropy method to calculate the risk of capacity deficit of a composite power system. By applying importance sampling for load states in addition to generation and transmission states in a systematic manner, the proposed method is many orders of magnitude more efficient than crude Monte Carlo simulation and considerably more efficient than other Cross-Entropy based algorithms that apply other ways of estimating the importance sampling distributions. An effective performance metric of system states is applied in order to find optimal importance sampling distributions during pre-simulation that significantly reduces the required computational effort. Simulations, using well known IEEE reliability test systems, show that even problems that are nearly intractable using crude Monte Carlo simulation become very manageable using the proposed method., Part of proceedings: ISBN 978-1-5090-4237-1QC 20220921

State estimation is an essential part of energy management system in smart grid as it is a basis for many of the associated management and control processes. In this paper, we present a decentralized state estimation approach, based on consensus optimization and the alternating direction method of multipliers, that is robust against certain harsh class of false data injection schemes. The proposed scheme provides a reliable estimate of the global system state in a distributed manner even if the system is regionally unobservable to some regional controllers, but globally observable across regions. The scheme also accommodates different communication network topologies for a given power network. We assess the performance of the presented schemes on IEEE 14 and 118 bus test systems.

This paper presents results from the KIC InnoEnergy project: Generic DC grid off-line and real-time simulation models and tools (Action 2.1, Subtask 2.1.1). The work reported here is focused on the development of a generic voltage source converter (VSC) model and its control schemes. Different test systems were designed and implemented in simulation tools and an experimental platform to verify the proposed generic model. Consistent simulation and emulation performances indicate that the generic model and its control schemes are applicable for VSC-HVDC operation, and thus, they can facilitate further research and development in DC grids., QC 20160404

To better understand the challenges encountered by users and developers of automatic software testing, we have performed an empirical investigation of a discussion board used for support of a test automation framework having several hundred users. The messages on the discussion board were stratified into problem reports, help requests, development information, and feature requests. The messages in the problem report and help request strata were then sampled and analyzed using thematic analysis, searching for common patterns. Our analysis indicate that a large part of the impediments discussed on the board are related to issues related to the centralized IT environment, and to erroneous behavior connected to the use of the framework and related components. We also observed a large amount of impediments related to the use of software development tools. Turning to the help requests, we found that the majority of the help requests were about designing test scripts and not about the areas that appear to be most problematic. From our results and previous publications, we see a clear need to simplify the use, installation, and configuration of test systems of this type. The problems attributable to software development tools suggest that testers implementing test automation need more skills in handling those tools, than historically has been assumed. Finally, we propose that further research into the benefits of centralization of tools and IT environments, as well as structured deployment and efficient use of test automation, is performed.

This paper is concerned with studying how the minimum power loss in a power system is related to its network topology. The existing algorithms in the literature all exploit nonlinear, heuristic, or local search algorithms to find the minimum power loss, which make them blind to the network topology. Given certain constraints on power level, bus voltages, etc., a linear-matrix-inequality (LMI) optimization problem is derived, which provides a lower bound on the minimum active loss in the network. The proposed LMI problem has the property that its objective function depends on the loads and its matrix inequality constraint is related to the topology of the power system. This property makes it possible to address many important power problems, such as the optimal network reconfiguration and the optimal placement/sizing of distributed generation units in power systems. Moreover, a condition is provided under which the solution of the given LMI problem is guaranteed to be exactly equal to the minimum power loss. As justified mathematically and verified on IEEE test systems, this condition is expected to hold widely in practice, implying that a practical power loss minimization problem is likely to be solvable using a convex algorithm.

This paper presents a conceptual approach for eliminating the multiple estimation problem of impedance-based fault location methods applied to power distribution systems, using the available measurements of current and voltage fundamentals at the power substation. Three test systems are used to identify the faulted lateral obtaining high performance, even in the case of similar feeder configurations. This approach shows that it is possible to obtain a unique fault location, eliminating the problem of multiple estimation in tree-shaped radial systems using the single-end measurements at the distribution substation. Finally, this approach also contributes to improve the power continuity indexes in distribution systems by the opportune zone fault location., Electrical Engineering, Mathematics and Computer Science

This paper presents a conceptual approach for eliminating the multiple estimation problem of impedance-based fault location methods applied to power distribution systems, using the available measurements of current and voltage fundamentals at the power substation. Three test systems are used to identify the faulted lateral obtaining high performance, even in the case of similar feeder configurations. This approach shows that it is possible to obtain a unique fault location, eliminating the problem of multiple estimation in tree-shaped radial systems using the single-end measurements at the distribution substation. Finally, this approach also contributes to improve the power continuity indexes in distribution systems by the opportune zone fault location., Electrical Engineering, Mathematics and Computer Science

This paper presents an iterative approach to jointly estimate the states in combined heat and power systems (CHPS). The node method is used to address the temperature quasi-dynamics in the district heating system (DHS), resulting in a dynamic state estimation (DSE) model. An alternating estimation strategy is employed to effectively handle the complicated time-delay constraints of temperature in the computation of DSE. Case studies are conducted on two CHPS test systems to verify the effectiveness of the DSE and the alternating approach. Simulation results show that the DSE in CHPS outperforms the static state estimation and the separate state estimation in individual energy systems in terms of accuracy.

Since extended power outages causes severe stress on society and the restoration following a black out is a complex and time consuming task, efficient restoration strategies are needed. During the restoration, the power system undergoes continual changes and therefore it is subject to desired and undesired operations and failures which might be devastating. The main contribution of this paper is a new method to estimate the risk of an uncontrolled system separation in case of a loss of a transmission line or a transformer during a restoration process. The method in this paper assigns failure rates to the transformers and the transmission lines. Further, a graph theoretical method are used to find probability bounds for an uncontrolled system separation for a whole restoration sequence. In a numerical example are three restoration strategies applied to an IEEE 14 bus test system and evaluated. It is shown in the numerical example that the restoration strategy has an high impact on the probability for a system separation., QC 20240110

Since extended power outages causes severe stress on society and the restoration following a black out is a complex and time consuming task, efficient restoration strategies are needed. During the restoration, the power system undergoes continual changes and therefore it is subject to desired and undesired operations and failures which might be devastating. The main contribution of this paper is a new method to estimate the risk of an uncontrolled system separation in case of a loss of a transmission line or a transformer during a restoration process. The method in this paper assigns failure rates to the transformers and the transmission lines. Further, a graph theoretical method are used to find probability bounds for an uncontrolled system separation for a whole restoration sequence. In a numerical example are three restoration strategies applied to an IEEE 14 bus test system and evaluated. It is shown in the numerical example that the restoration strategy has an high impact on the probability for a system separation., QC 20240110

Since extended power outages causes severe stress on society and the restoration following a black out is a complex and time consuming task, efficient restoration strategies are needed. During the restoration, the power system undergoes continual changes and therefore it is subject to desired and undesired operations and failures which might be devastating. The main contribution of this paper is a new method to estimate the risk of an uncontrolled system separation in case of a loss of a transmission line or a transformer during a restoration process. The method in this paper assigns failure rates to the transformers and the transmission lines. Further, a graph theoretical method are used to find probability bounds for an uncontrolled system separation for a whole restoration sequence. In a numerical example are three restoration strategies applied to an IEEE 14 bus test system and evaluated. It is shown in the numerical example that the restoration strategy has an high impact on the probability for a system separation., QC 20240110

Since extended power outages causes severe stress on society and the restoration following a black out is a complex and time consuming task, efficient restoration strategies are needed. During the restoration, the power system undergoes continual changes and therefore it is subject to desired and undesired operations and failures which might be devastating. The main contribution of this paper is a new method to estimate the risk of an uncontrolled system separation in case of a loss of a transmission line or a transformer during a restoration process. The method in this paper assigns failure rates to the transformers and the transmission lines. Further, a graph theoretical method are used to find probability bounds for an uncontrolled system separation for a whole restoration sequence. In a numerical example are three restoration strategies applied to an IEEE 14 bus test system and evaluated. It is shown in the numerical example that the restoration strategy has an high impact on the probability for a system separation., QC 20240110

Since extended power outages causes severe stress on society and the restoration following a black out is a complex and time consuming task, efficient restoration strategies are needed. During the restoration, the power system undergoes continual changes and therefore it is subject to desired and undesired operations and failures which might be devastating. The main contribution of this paper is a new method to estimate the risk of an uncontrolled system separation in case of a loss of a transmission line or a transformer during a restoration process. The method in this paper assigns failure rates to the transformers and the transmission lines. Further, a graph theoretical method are used to find probability bounds for an uncontrolled system separation for a whole restoration sequence. In a numerical example are three restoration strategies applied to an IEEE 14 bus test system and evaluated. It is shown in the numerical example that the restoration strategy has an high impact on the probability for a system separation., QC 20240110