References of "Weckesser, Johannes"
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See detailSearching for Plausible N-k Contingencies Endangering Voltage Stability
Weckesser, Johannes ULg; Van Cutsem, Thierry ULg

in IEEE International Conference on Innovative Smart Grid Technologies IEEE ISGT Europe 2017, Turin 26-29 September 2017 (in press)

This paper presents a novel search algorithm using time-domain simulations to identify plausible N-k contingencies endangering voltage stability. Starting from an initial list of disturbances ... [more ▼]

This paper presents a novel search algorithm using time-domain simulations to identify plausible N-k contingencies endangering voltage stability. Starting from an initial list of disturbances, progressively more severe contingencies are investigated. After simulation of a N-k contingency, the simulation results are assessed. If the system response is unstable, a plausible harmful contingency sequence has been found. Otherwise, components affected by the contingencies are considered as candidate next event leading to N-(k+1) contingencies. This implicitly takes into account hidden failures of component protections. The performance of the proposed search algorithm is compared to a brute-force algorithm and demonstrated on the IEEE Nordic test system. [less ▲]

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See detailAn Equivalent to Represent Inertial and Primary Frequency Control Effects of an External System
Weckesser, Johannes ULg; Van Cutsem, Thierry ULg

in IET Generation, Transmission & Distribution (in press)

This paper presents a novel equivalent, which is suitable for simulation of inertial and primary frequency control effects. In the model reduction procedure, dynamic power injectors are used to replace ... [more ▼]

This paper presents a novel equivalent, which is suitable for simulation of inertial and primary frequency control effects. In the model reduction procedure, dynamic power injectors are used to replace the external system and to mimic its dynamic behavior. The parameters of the equivalents are tuned with a simple approach presented in this paper. The effectiveness of the proposed method is demonstrated on a modified version of the ENTSO-E Dynamic Study Model. The results show that the system frequency response of the unreduced system is retained and a speedup of the simulations of around 4.0 is achieved. [less ▲]

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See detailA Model Reduction Approach for Simulation of Long-term Voltage and Frequency Dynamics
Weckesser, Johannes ULg; Franz, Valeri; Grebe, Eckhard et al

in 12th IEEE PES PowerTech Conference 2017 (2017, June)

This paper presents a novel approach, which identifies a buffer zone around a given study system and replaces the external system with an equivalent. The aim is to obtain a reduced system, which is ... [more ▼]

This paper presents a novel approach, which identifies a buffer zone around a given study system and replaces the external system with an equivalent. The aim is to obtain a reduced system, which is suitable for assessment of long-term voltage and frequency dynamics in the study system. First, the proposed methodology ensures that all components, which are impacting the voltage profile of the study system, are included in the buffer zone. For that purpose, the propagation of reactive power changes from the boundary of the study system into the external system are used in a modified depth-first search algorithm to identify the buffer zone. Second, the external system is replaced with equivalents accounting for inertia and primary frequency control effects. The proposed method was successfully tested on a modified version of the ENTSO-E Dynamic Study Model. [less ▲]

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See detailA decision support tool for transient stability preventive control
Pertl, Michael; Weckesser, Johannes ULg; Rezkalla, Michel et al

in Electric Power Systems Research (2017), 147

The paper presents a decision support tool for transient stability preventive control contributing to increased situation awareness of control room operators by providing additional information about the ... [more ▼]

The paper presents a decision support tool for transient stability preventive control contributing to increased situation awareness of control room operators by providing additional information about the state of the power system in terms of transient stability. A time-domain approach is used to assess the transient stability for potentially critical faults. Potential critical fault locations are identified by a critical bus screening through analysis of pre-disturbance steady-state conditions. The identified buses are subject to a fast critical contingency screening determining the actual critical contingencies/buses. These two screenings aim at reducing the computational burden of the assessment, since only contingencies considered as critical are taken into account. The critical clearing times for the critical contingencies are determined. A preventive re-dispatch of generators to ensure a predefined minimum critical clearing time for faults at all buses is proposed, while costs are minimized. The results of the assessment are presented to the control room operator, who decides to accept the suggested dispatch or to repeat the assessment considering additional user-specific constraints. The effectiveness of the proposed method is demonstrated on a standard nine-bus and the New England test system. [less ▲]

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See detailAn Improved On-line Contingency Screening for Power System Transient Stability Assessment
Weckesser, Johannes ULg; Jóhannsson, Hjörtur; Glavic, Mevludin ULg et al

in Electric Power Components & Systems (2017)

This paper presents a contingency screening method and a framework for its on-line implementation. The proposed method carries out contingency screening and on-line stability assessment with respect to ... [more ▼]

This paper presents a contingency screening method and a framework for its on-line implementation. The proposed method carries out contingency screening and on-line stability assessment with respect to first-swing transient stability. For that purpose, it utilizes the single machine equivalent method and aims at improving the prior developed contingency screening approaches. In order to determine vulnerability of the system with respect to a particular contingency, only one time-domain simulation needs to be performed. An early stop criteria is proposed so that in a majority of the cases the simulation can be terminated after a few hundred milliseconds of simulated system response. The method’s outcome is an assessment of the system’s stability and a classification of each considered contingency. The contingencies are categorized by exploiting parameters of an equivalent one machine infinite bus system. A novel island detection approach, appropriate for an on-line application since it utilizes efficient algorithms from graph theory and enables stability assessment of individual islands, is also introduced. The New England and New York system as well as the large-scale model of the Continental-European interconnected system are used to test the proposed method with respect to assessment accuracy and computation time. [less ▲]

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See detailLocal Identification of Voltage Instability from Load Tap Changer Response
Weckesser, Johannes ULg; Papangelis, Lampros ULg; Vournas, Costas et al

in Sustainable Energy, Grids and Networks (2017)

This paper presents a local long-term voltage instability monitoring method, which is suitable for on-line applications. The proposed extended-time Local Identification of Voltage Emergency Situations ... [more ▼]

This paper presents a local long-term voltage instability monitoring method, which is suitable for on-line applications. The proposed extended-time Local Identification of Voltage Emergency Situations (eLIVES) method is a significantly modified version of the previously presented LIVES method. The new method is not bound to assessing system response over a predefined LTC tapping period. This allows handling LTCs with variable delays, as well as events taking place during the tapping sequence impacting the distribution voltages. For that purpose, eLIVES applies recursive least square fitting to acquired distribution voltage measurements and a new set of rules to detect a voltage emergency situation. The effectiveness of the eLIVES method is presented on the IEEE Nordic test system for voltage stability and security assessment. [less ▲]

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See detailReal-time remedial action against aperiodic small signal rotor angle instability
Weckesser, Johannes ULg; Jóhannsson, Hjörtur; Østergaard, Jacob

in IEEE Transactions on Power Systems (2016), 31(1), 387-396

This paper presents a method that in real-time determines remedial actions, which restore stable operation with respect to aperiodic small signal rotor angle stability (ASSRAS) when insecure or unstable ... [more ▼]

This paper presents a method that in real-time determines remedial actions, which restore stable operation with respect to aperiodic small signal rotor angle stability (ASSRAS) when insecure or unstable operation has been detected. An ASSRAS assessment method is used to monitor the stability boundary for each generator in real-time. The ASSRAS boundary represents the condition when a generator reaches the maximum steady state active power injection. The proposed control method exploits analytically derived expressions for the ASSRAS boundary and other characteristic curves in the injection impedance plane to determine an active power redispatch among selected generators to restore stable and secure operation. Since the method is purely based on analytically derived expression, the computation of the remedial actions is fast and well suited for real-time operation. The method was tested on the IEEE 14-bus and the Nordic32 test systems where results show that the method can efficiently determine the required active power redispatch to avoid an imminent instability. [less ▲]

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See detailOn-line Dynamic Security Assessment in Power Systems.
Weckesser, Johannes ULg

Doctoral thesis (2015)

The thesis concerns the development of tools and methods for on-line dynamic security assessment (DSA). In a future power system with low-dependence or even independence of fossil fuels, generation will ... [more ▼]

The thesis concerns the development of tools and methods for on-line dynamic security assessment (DSA). In a future power system with low-dependence or even independence of fossil fuels, generation will be based to a large extent on non-controllable renewable energy sources (RES), such as wind and solar radiation. Moreover, ongoing research suggests that demand response will be introduced to maintain power balance between generation and consumption at all times. % as well as to account for forecasting inaccuracies related to power generation from RES. Due to these changes, the operating point of the power system will be less predictable. Consequently, today's stability and security assessment tools, which are generally dependent on extensive off-line studies, may no longer be feasible in their current development state. A core component of an efficient on-line dynamic security assessment is a fast and reliable contingency screening. As part of this thesis a contingency screening method is developed and its performance is assessed utilizing a set of test cases. The developed method reliably assesses first-swing transient angular stability of a power system in its current state with respect to a given set of contingencies. In order to ensure fast performance of the screening method, first a review of existing transient stability assessment (TSA) methods was carried out and their computational complexity was investigated. This allowed to identify the single machine equivalent (SIME) method as the potentially fastest assessment method and, hence, well suited for on-line DSA. Means for further performance improvement of the SIME method are investigated such as the reduction of the degree of system model detail used in time-domain simulation. This results in a recommendation for the required model detail for synchronous generator. A challenging task when using the SIME method is to early and reliably determine the critical machine cluster, which is the group of generators likely to lose synchronism. Therefore, a novel approach to identify the critical machine cluster is proposed in the thesis. This approach uses a new coupling coefficient, which is a measure of the coupling strength of pairs of generators, and a simple clustering algorithm to identify the critical group of generators. In order to determine a system to be transient secure, it is not sufficient to solely assess if all synchronous generators remain in synchronism, it is also required that the bus voltages remain within acceptable limits. A transient disturbance and the following angular divergence of a group of generators can cause critical voltage sags at certain buses in the system. In this thesis assessment of such voltage sags is proposed using two types of sensitivities, which are derived from the algebraic network equations. These sensitivities are derived after an in-depth study of the mechanism causing the voltage sags. The first sensitivity type is called load voltage sensitivity and allows identifying which bus voltages are affected by a change in rotor angle of a particular generator. % It is shown that the derived load voltage sensitivities for example allow to determine the contribution of each generator to an observed voltage sag, which is valuable information for identifying preventive controls. The second proposed type is called generator power sensitivity, which provides information on the effect of load variation on the generator's power injection. It is shown that the derived sensitivities can give valuable information to identify critical generator-load pairs as well as locations for applying preventive or remedial control measures. Furthermore, the development of a method for early prediction of critical voltage sags is described. The method's performance is compared to other prediction approaches. The results show that the proposed method succeeds in early, accurately and consistently predicting critically low voltage sags. An efficient on-line DSA not only identifies unstable or insecure operation, but also proposes preventive or remedial control actions to restore stability and security in the system. In this thesis a further development of a method for determining real-time remedial action against aperiodic small signal rotor angle instability is described. A real-time aperiodic small signal rotor angle stability assessment method is employed to monitor the respective stability boundary and to compute the respective stability margin of each generator in the system. In case that the stability margin of a particular generator falls below a pre-defined security threshold, the proposed method analytically determines power generation re-dispatch solutions, which restore stable and secure operation in the system. The effectiveness of the method is presented on two test cases in two different test systems. [less ▲]

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See detailCritical machine cluster identification using the equal area criterion
Weckesser, Johannes ULg; Jóhannsson, Hjörtur; Østergaard, Jacob

in Proceedings of 2015 IEEE Power & Energy Society General Meeting (2015)

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See detailImpact of Model Detail of Synchronous Machines on Real-time Transient Stability Assessment
Weckesser, Johannes ULg; Jóhannsson, Hjörtur; Østergaard, Jacob

in Proceedings of 2013 IREP Symposium (2013)

In this paper, it is investigated how detailed the model of a synchronous machine needs to be in order to assess transient stability using a Single Machine Equivalent (SIME). The results will show how the ... [more ▼]

In this paper, it is investigated how detailed the model of a synchronous machine needs to be in order to assess transient stability using a Single Machine Equivalent (SIME). The results will show how the stability mechanism and the stability assessment are affected by the model detail. In order to identify the transient stability mechanism, a simulation with a high-order model was used as reference. The Western System Coordinating Council System (WSCC) and the New England & New York system are considered and simulations of an unstable and a stable scenario are carried out, where the detail of the machine models is varied. Analyses of the results suggest that a 4th -order model may be sufficient to represent synchronous machines in transient stability studies. [less ▲]

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See detailInvestigation of the Adaptability of Transient Stability Assessment Methods to Real-Time Operation
Weckesser, Johannes ULg; Jóhannsson, Hjörtur; Sommer, Stefan et al

in IEEE PES Innovative Smart Grid Technologies Conference Europe (2012)

In this paper, an investigation of the adaptability of available transient stability assessment methods to real-time operation and their real-time performance is carried out. Two approaches based on ... [more ▼]

In this paper, an investigation of the adaptability of available transient stability assessment methods to real-time operation and their real-time performance is carried out. Two approaches based on Lyapunov’s method and the equal area criterion are analyzed. The results allow to determine the runtime of each method with respect to the number of inputs. Furthermore, it allows to identify, which method is preferable in case of changes in the power system such as the integration of distributed power resources (DER). A comparison of the performance of the analyzed methods leads to the suggestion that matrix reduction and time domain simulation are the most critical operations. [less ▲]

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See detailReal-Time Stability Assessment based on Synchrophasors
Jóhannsson, Hjörtur; Garcia-Valle, Rodrigo; Weckesser, Johannes ULg et al

in IEEE PES Trondheim PowerTech (2011)

In this paper, an overview is provided of a new method that in real-time provides an early warning for an emerging blackout that are characterized by a slowly increasing angular separation between sub ... [more ▼]

In this paper, an overview is provided of a new method that in real-time provides an early warning for an emerging blackout that are characterized by a slowly increasing angular separation between sub-groups of system generators. Such angular separation between subgroups of generators can eventually cause in very sharp decline in system voltages at intermediate locations between the two groups as the angular separation approaches 180 degree. In order to receive an early warning for the occurrence of such type of blackouts, the boundaries of the system generators aperiodic small-signal stability are suggested to be monitored. For that purpose, method for real-time assessment of aperiodic small-signal rotor angle stability is presented. The approach is based on an element-wise assessment of individual synchronous machines where the aim is to determine the maximum steady state power that each synchronous generator can inject into the system. The limits for maximum injectable power represent the boundary for aperiodic small signal stability. The concept of the proposed method is tested on two different systems. The results show that the method is capable of accurately detecting when a given machine crosses the stability boundary. The method can as well provide in real-time a margin to the machines stability boundary, which can be used as an early warning for an impending system stability problem. [less ▲]

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