27 research outputs found

    Power System Digital Twins and Real-Time Simulations in Modern Grids

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    Power systems are in a state of constant change with new hardware, software and applications affecting their planning, operation, and maintenance. Power system control centers are also evolving through new technologies and functionalities to adapt to current needs. System control rooms have moved from fully manual to automated operations, from analog to digital, and have become an embedded and complex information, communication, computation and control system. Digital twins are virtual representations of physical systems, assets and/or processes. They are enabled through software, hardware and data integration, and allow real-time monitoring, controlling, prediction, optimization, and improved decision-making. Consequently, digital twins arise as a technology capable of incorporating existing control systems along with new ones to collect, classify, store, retrieve and disseminate data for the future generation of control centers. Power system digital twins (PSDTs) can uplift how data from power grids and their equipment is processed, providing operators new ways to visualize and understand the information. Nevertheless, complexity and size of modern power systems narrow the scope a current digital twin can have. Furthermore, the services provided are limited to only certain phenomena and/or applications. This thesis addresses the need for a flexible and versatile solution that is also robust and adaptable for monitoring, operating and planning future power systems. The modular design for implementation of the next generation of PSDTs is proposed based on grid applications and/or services they can provide. From a modeling perspective, this thesis also distinguishes how real-time simulations enable the design, development, and operation of a PSDT. First, the need for enhanced power system modeling and simulation techniques is established. Moreover, the necessity of expanding to a more complete and varied open-source library of power system models is identified. The thesis continues by designing, developing, and testing models of inverter-based resources that can be used by the industry and researchers when developing PSDTs. Furthermore, the first-of-its-kind synthetic grid with a longitudinal structure, the S-NEM2300-bus benchmark model, based on the Australian National Electricity Market is created. The synthetic grid is, finally, used to illustrate the first steps towards implementing a practical PSDT

    Frequency Characterization and Control for Future Low Inertia Systems

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    Oscillation Analysis and its Mitigation Using Inverter-Based Resources in Large-Scale Power Grids

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    In today\u27s interconnected power grids, forced oscillations and poorly damped low-frequency oscillations are major concerns that can damage equipment, limit power transfer capability, and deteriorate power system stability. The first part of the dissertation focuses on the impact of a wide-area power oscillation damping (POD) controller via voltage source converter-based high voltage direct current (VSC-HVDC) in enhancing the power system stability and improving the damping of low-frequency oscillation. The POD controller\u27s performance was investigated under a three-phase temporary line fault. The Great Britain (G.B.) power grid model validated the POD controller performance via active power modulation of VSC-HVDC through TSAT-RTDS hybrid simulation. The developed POD controller is also implemented on a general-purpose hardware platform CompactRIO and tested on a hardware-in-the-loop (HIL) test setup with actual PMU devices and a communication network impairment simulator. A variety of real-world operating conditions is considered in the HIL tests, including measurement error/noise, occasional/consecutive data package losses, constant/random time delays, and multiple backups PMUs. The second part of the dissertation proposes a two‐dimensional scanning forced oscillation grid vulnerability analysis method to identify areas/zones and oscillation frequency in the system critical to forced oscillation. These critical areas/zones can be considered effective actuator locations to deploy forced oscillation damping controllers. Additionally, a POD controller through inverter-based resources (IBRs) is proposed to reduce the forced oscillation impact on the entire grid. The proposed method is tested when the external perturbation is active power and compared with the reactive power perturbation result. The proposed method is validated through a case study on the 2000-bus synthetic Texas power system model. The simulation results demonstrate that the critical areas/zones of forced oscillation are related to the areas that highly participate in the natural oscillation. Furthermore, forced oscillation through active power disturbance can have a more severe impact than reactive power disturbance, especially at resonance. The proposed forced oscillation controller can mitigate the impact of the forced oscillation on the entire system when the actuator is close to the forced oscillation source. In addition, active power modulation of IBR can provide better damping performance than reactive power modulation

    IMPROVING A TRANSIENT STABILITY CONTROL SCHEME WITH WIDE-AREA SYNCHROPHASORS AND THE MICROWECC, A REDUCED-ORDER MODEL OF THE WESTERN INTERCONNECT

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    This thesis is composed of two research projects. The first project investigated the feasibility of improving a generator tripping control scheme using wide-area synchrophasors and the second project focused on building a reduced-order model of the western North American power system (wNAPS) for use in a real-time digital simulator. Transient stability is a major reliability issue for power systems. Radially-connected power plants are especially prone to transient stability problems. An example of this is the fourgenerator Colstrip power plant located in southeast Montana, USA. The Colstrip generators are protected by a tripping control system called the Acceleration Trend Relay (ATR) that is designed to disconnect generators during system disturbances to prevent asynchronous operation and further system instability. Like most transient stability tripping schemes, the ATR relies entirely on local information. However, because transient stability is a wide-area phenomenon determined by the relative synchronism of the system, local information can produce misoperations causing the ATR to false trip. The first part of this thesis studied the feasibility of using wide-area synchrophasors provided by phasor measurement units (PMUs) to improve protection schemes such as the ATR. Transient stability software was used to model the ATR and evaluate the benefits of adding wide-area measurements to the control scheme. Real-time simulators are effective tools for studying power systems because they can accurately reproduce electromechanical dynamics while allowing for prototype controllers to be physically connected. However, they impose serious limitations on the size of systems that can be modeled. Model order reduction techniques can be used to lower the computational complexity of a system while approximating the dynamics of the original model. The second part of this thesis presents a reduced-order model of the wNAPS termed the “MicroWECC.” The MicroWECC is a further reduction of the MiniWECC model and was designed to have approximate impedance, generation, and modal characteristics. The model was constructed in two positive-sequence transient simulation tools and then modal analysis was performed to compare the MicroWECC to the MiniWECC model. Parameters for electromagnetic transient program (EMTP) models were also suggested

    Real-Time Analysis of an Active Distribution Network - Coordinated Frequency Control for Islanding Operation

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    Operation and control of voltage source converters in transmission networks for AC system stability enhancement

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    The rapid expansion in power transmission for the integration of large-scale renewables is foreseen in the future. This will be complemented by infrastructure reinforcements in the form of series compensation and high-voltage direct current (HVDC) links. These changes will bring forth new operability challenges to grid operators. The stability issues pertained to such reinforcements: potential threat of subsynchronous resonance (SSR) and frequency regulation will be investigated in this thesis. Utilising the existing and future voltage source converters (VSC) based HVDC links to support the AC system by proving ancillary services will be of significant importance in the coming decades. The research work presented in this thesis is aimed to address these challenges, in particular, the technical barriers associated with AC/DC interaction and to propose measures to avoid any potential instability. The main contributions of this research work comprise of four parts, namely, (1) analysis of interactions in-terms of SSR in AC/DC grids, (2) design of SSR damping (SSRD) controllers, (3) experimental demonstration of SSRD schemes, and (4) assessment and improvement of frequency regulation in a wind-thermal bundled AC/DC grid. An VSC-HVDC connected series-compensated AC system resembling the Great Britain (GB) power system has been used as the test network to evaluate the operability challenges pertained to the reinforcements. A state-space representation has been formulated and an eigenvalue analysis has been performed to assess the impact of VSC-HVDC on the torsional modes of nearby connected thermal generation plants. This is followed by damping torque investigation for SSR screening with the results compared against time-domain simulations for testing the accuracy of the small-signal models for SSR studies. A series of SSRD schemes is presented which have been integrated with the VSC-HVDC to damp SSR in the series-compensated GB power system. In addition, this thesis proposes an adaptive SSRD method based on the real-time estimation of the subsynchronous frequency v Abstract component present in series-compensated transmission lines–key information for the optimal design of HVDC subsynchronous damping controllers. Furthermore, the combined AC/DC GB network has been implemented in a real-time digital simulator and connected to a VSCHVDC scaled-down test-rig to performhardware-in-the-loop tests. The efficacy and operational performance of the AC/DC network while providing SSR damping is tested through a series of experiments. In order to provide frequency support in a wind-thermal bundled AC/DC system a dualdroop controlmethod is presented. The scheme binds the system frequency with the DC voltage of an HVDC network. For completeness, the performance of the proposed method is compared to conventional frequency regulation schemes. Sensitivity studies and eigenvalue analyses are conducted to assess the impact that wind penetration and changes in the dual-droop coefficient have on grid stability. Experimental validation is performed using a real-time hardware-inthe- loop test-rig, with simulation and experimental results showing a good agreement and evidencing the superior performance of the proposed frequency support scheme

    Machine Learning assisted Digital Twin for event identification in electrical power system

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    The challenges of stable operation in the electrical power system are increasing with the infrastructure shifting of the power grid from the centralized energy supply with fossil fuels towards sustainable energy generation. The predominantly RES plants, due to the non-linear electronic switch, have brought harmonic oscillations into the power grid. These changes lead to difficulties in stable operation, reduction of outages and management of variations in electric power systems. The emergence of the Digital Twin in the power system brings the opportunity to overcome these challenges. Digital Twin is a digital information model that accurately represents the state of every asset in a physical system. It can be used not only to monitor the operation states with actionable insights of physical components to drive optimized operation but also to generate abundant data by simulation according to the guidance on design limits of physical systems. The work addresses the topic of the origin of the Digital Twin concept and how it can be utilized in the optimization of power grid operation.Die Herausforderungen fĂŒr den zuverfĂ€ssigen Betrieb des elektrischen Energiesystems werden mit der Umwandlung der Infrastruktur in Stromnetz von der zentralen Energieversorgung mit fossilen Brennstoffen hin zu der regenerativen Energieeinspeisung stetig zugenommen. Der Ausbau der erneuerbaren Energien im Zuge der klimapolitischen Zielsetzung zur COÂČ-Reduzierung und des Ausstiegs aus der Kernenergie wird in Deutschland zĂŒgig vorangetrieben. Aufgrund der nichtlinearen elektronischen Schaltanlagen werden die aus EE-Anlagen hervorgegangenen Oberschwingungen in das Stromnetz eingebracht, was nicht nur die KomplexitĂ€t des Stromnetzes erhöht, sondern auch die StabilitĂ€t des Systems beeinflusst. Diese Entwicklungen erschweren den stabilen Betrieb, die Verringerung der AusfĂ€lle und das Management der Netzschwankungen im elektrischen Energiesystem. Das Auftauchen von Digital Twin bringt die Gelegenheit zur Behebung dieser Herausforderung. Digital Twin ist ein digitales Informationsmodell, das den Zustand des physikalischen genau abbildet. Es kann nicht nur zur Überwachung der BetriebszustĂ€nde mit nachvollziehbarem Einsichten ĂŒber physischen Komponenten sondern auch zur Generierung der Daten durch Simulationen unter der BerĂŒcksichtigung der Auslegungsgrenze verwendet werden. DiesbezĂŒglich widmet sich die Arbeit zunĂ€chste der Fragestellung, woher das Digital Twin Konzept stammt und wie das Digitan Twin fĂŒr die Optimierung des Stromnetzes eingesetzt wird. HierfĂŒr werden die Perspektiven ĂŒber die dynamische ZustandsschĂ€tzung, die Überwachung des des Betriebszustands, die Erkennung der Anomalien usw. im Stromnetz mit Digital Twin spezifiziert. Dementsprechend wird die Umsetzung dieser Applikationen auf dem Lebenszyklus-Management basiert. Im Rahmen des Lebenszyklusschemas von Digital Twin sind drei wesentliche Verfahren von der Modellierung des Digital Twins zur deren Applizierung erforderlich: Parametrierungsprozess fĂŒr die Modellierung des Digital Twins, Datengenerierung mit Digital Twin Simulation und Anwendung mit Machine Learning Algorithmus fĂŒr die Erkennung der Anomalie. Die Validierung der ZuverlĂ€ssigkeit der Parametrierung fĂŒr Digital Twin und der Eventserkennung erfolgt mittels numerischer Fallstudien. Dazu werden die Algorithmen fĂŒr Online und Offline zur Parametrierung des Digital Twins untersucht. Im Rahmen dieser Arbeit wird das auf CIGRÉ basierende Referenznetz zur Abbildung des Digital Twin hinsichtlich der Referenzmessdaten parametriert. So sind neben der Synchronmaschine und Umrichter basierende Einspeisung sowie Erreger und Turbine auch regler von Umrichter fĂŒr den Parametrierungsprozess berĂŒcksichtigt. Nach der Validierung des Digital Twins werden die zahlreichen Simulationen zur Datengenerierung durchgefĂŒhrt. Jedes Event wird mittels der Daten vo Digital Twin mit einem "Fingerprint" erfasst. Das Training des Machine Learning Algorithmus wird dazu mit den simulierten Daten von Digital Twin abgewickelt. Das Erkennungsergebnis wird durch die Fallstudien validiert und bewertet

    Grid connection of offshore wind farms through multi-terminal high voltage direct current networks

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    This thesis investigated the capability of multi-terminal high voltage direct current (HVDC) networks based on voltage source converter (VSC) technology to transfer power generated from offshore wind farms to onshore grids and interconnect the grids of different countries. Variable speed wind turbines and other low-carbon generators or loads that are connected through inverters do not inherently contribute to the inertia of AC grids. A coordinated control scheme for frequency support from multi-terminal VSC-HVDC (MTDC) scheme was designed to transfer additional power to AC grids from the kinetic energy stored in the wind turbine rotating mass and the active power transferred from other AC systems. The wind turbine inertia response limited the rate of change of AC grid frequency and the active power transferred from the other AC system reduced the frequency deviation. The wind turbines recovered back to their original speed after their inertia response and transferred a recovery power to the AC grid. An alternative coordinated control scheme with a frequency versus active power droop controller was designed for frequency support from MTDC schemes, in order to transfer the recovery power of wind turbines to other AC systems. This prevented a further drop of frequency on the AC grid. The effectiveness of the alternative coordinated control scheme was verified using the PSCAD simulation tool and demonstrated using an experimental test rig. A scaling method was demonstrated for a multi-terminal DC test rig to represent the equivalent steady state operation of different VSC-HVDC systems. The method uses a virtual resistance to extend the equivalent DC cable resistance of the test rig through the action of an additional DC voltage versus DC current droop controller. Three different VSC-HDC systems were modelled using the PSCAD simulation tool and demonstrated on the DC test rig with virtual resistance, showing good agreement
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