Search results

(1 - 4 of 4)
SECURE AND RESILIENT OPERATION OF CYBER-PHYSICAL POWER SYSTEMS
Title
SECURE AND RESILIENT OPERATION OF CYBER-PHYSICAL POWER SYSTEMS
Creator
Li, Zhiyi
Date
2017, 2017-07
Description
For economic reasons, modern power systems are commonly operated close to their secure limits so that they are vulnerable to unexpected severe...
Show moreFor economic reasons, modern power systems are commonly operated close to their secure limits so that they are vulnerable to unexpected severe disruptions such as disastrous cyberattacks and extreme weather events. This thesis is aimed at enhancing the security and resilience of power supplies for facilitating the development of a Smart Grid, when power systems in various parts of the world have been undergoing transitions toward cyber-physical systems. First, this thesis discusses common cybersecurity vulnerabilities in modern power systems and presents physical implications of cyberattacks on power system operations. In particular, this thesis analyzes a specifc type of coordinated cyberphysical attacks that could lead to undetectable line outages. Coordinated with physical attacks causing line outages, cyberattacks comprising topology preserving and load redistribution attacks could mask and potentially exasperate the outages to trigger cascading failures. Such coordinated cyber-physical attacks are analyzed in a bi-level optimization model which is then transformed into a mixed-integer linear programming problem. The proposed model and the two-stage solution algorithm are examined by case studies based on the IEEE 14-bus and 118-bus test systems. Second, this thesis offers the pertinent studies on quantifying the risk of cybersecurity vulnerabilities in power system operations. A type of locally coordinated cyber-physical attacks is analyzed in detail, which would cause undetectable line outages in local areas without the need for complete network information. A risk-based optimization model in the mixed-integer linear programming form is presented for analyzing physical implications resulting from the power ow redistribution. An efficient greedy search-based heuristic method is then developed to offer satisfactory solutions for real-time applications, which are verified by case studies based on a six-bus system and the two-area IEEE RTS-96 system. Third, this thesis studies security measures for mitigating the cybersecurity risk in power system operations. A game-theoretic framework is built for determining the optimal combination of security measures based on the minimax-regret decision rule. The resulting multi-level optimization model is reformulated as a bilevel mixed-integer linear programming problem. An implicit enumeration algorithm is then developed to achieve an exact solution to this complex problem. Acceleration techniques are also provided to improve the computation efficiency for large-scale power system applications. The proposed model and solution methods are validated by case studies based on a six-bus test system and the two-area RTS-96 system. Fourth, this thesis extends the discussion of cybersecurity vulnerabilities to the operation of distributed power systems like microgrids. Since microgrids are regarded as building blocks of a Smart Grid, they strive for cyber-secure operations for sustaining power services to local customers. The assessment and mitigation of the cybersecurity risk in microgrid operations is then presented in depth. Additional opportunities provided by software-defined networking technologies to enhance the microgrid cybersecurity are also realized by the proposed defense-in-depth framework that comprises three lines of defense against cyberattacks. Last, this thesis investigates the role of networked microgrids in enhancing the power system resilience against extreme events. Since resilience is an intrinsically complex property which requires deep understanding of power system operations, a generic simulation-based framework is developed for power system operators to analyze the resilience comprehensively and respond effectively in emergency conditions. The notion that the deployment of networked microgrids catalyzes the resilience enhancement in a Smart Grid is discussed in detail. Besides, the management of networked microgrids for achieving a higher degree of resilience, reliability, and efficiency of power supplies is discussed based on the proposed hierarchical control framework.
Ph.D. in Electrical Engineering, July 2017
Show less
PMU DATA APPLICATIONS IN SMART GRID: LOAD MODELING, EVENT DETECTION AND STATE ESTIMATION
Title
PMU DATA APPLICATIONS IN SMART GRID: LOAD MODELING, EVENT DETECTION AND STATE ESTIMATION
Creator
Ge, Yinyin
Date
2016, 2016-05
Description
The thesis mainly includes four parts of research, event detection, data archival reduction, load modeling, state estimation. Firstly, we...
Show moreThe thesis mainly includes four parts of research, event detection, data archival reduction, load modeling, state estimation. Firstly, we present methods on real-time event detection and data archival reduction based on synchrophasor data produced by phasor measurement unit (PMU). Event detection is performed with Principal Component Analysis (PCA) and a second order difference method with a hierarchical framework for the event notification strategy on a small-scale Microgrid. Compared with the existing methods, the proposed method is more practical and efficient in the combined use of event detection and data archival reduction. Secondly, the proposed method on data reduction, which is an “Event oriented auto-adjustable sliding window method”, implements a curve fitting algorithm with a weighted exponential function-based variable sliding window accommodating different event types. It works efficiently with minimal loss in data information especially around detected events. The performance of the proposed method is shown on actual PMU data from the IIT campus Microgrid, thus successfully improving the situational awareness (SA) of the campus power system network. Thirdly, we present a new “event-oriented” method of online load modeling for the IIT Microgrid based on synchrophasor data produced PMU. Several load models and their parameter estimation methods are proposed. It is given great importance on choosing the best models for the detected events. The online load modeling process is based on an adjustable sliding window applied to two different types of load step changes. The load modeling tests and related analysis on the synchrophasor data of the IIT Microgrid are demonstrated in this paper. Finally, we present a three-phase unbalanced distribution system state estimation (DSSE) method based on Semidefinitetheir parameter estimation methods are proposed. It is given great importance on choosing the best models for the detected events. The online load modeling process is based on an adjustable sliding window applied to two different types of load step changes. The load modeling tests and related analysis on the synchrophasor data of the IIT Microgrid are demonstrated in this paper. Finally, we present a three-phase unbalanced distribution system state estimation (DSSE) method based on Semidefinite Programming (SDP). A partitioning strategy with the aid of PMU and another distributed optimization algorithm alternating direction method of multipliers (ADMM) are also proposed for large-scale DSSE. Compared with a traditional weighted least square (WLS) method based on the Gauss-Newton iteration, the proposed DSSE by SDP method delivers a more accurate estimation, and the application of ADMM can lead to high performance for large scale DSSE while deriving satisfying estimation.
Ph.D. in Electrical Engineering, May 2016
Show less
MICROGRIDS AND DISTRIBUTED GENERATION SYSTEMS: CONTROL, OPERATION,COORDINATION AND PLANNING
Title
MICROGRIDS AND DISTRIBUTED GENERATION SYSTEMS: CONTROL, OPERATION,COORDINATION AND PLANNING
Creator
Che, Liang
Date
2015, 2015-07
Description
Distributed Energy Resources (DERs) which include distributed generations (DGs), distributed energy storage systems, and adjustable loads are...
Show moreDistributed Energy Resources (DERs) which include distributed generations (DGs), distributed energy storage systems, and adjustable loads are key components in microgrid operations. A microgrid is a small electric power system integrated with onsite DERs to serve all or some portion of the local loads and connected to the utility grid through the point of common coupling (PCC). Microgrids can operate in both gridconnected mode and island mode. The structure and components of hierarchical control for a microgrid at Illinois Institute of Technology (IIT) are discussed and analyzed. Case studies would address the reliable and economic operation of IIT microgrid. The simulation results of IIT microgrid operation demonstrate that the hierarchical control and the coordination strategy of distributed energy resources (DERs) is an effective way of optimizing the economic operation and the reliability of microgrids. The benefits and challenges of DC microgrids are addressed with a DC model for the IIT microgrid. We presented the hierarchical control strategy including the primary, secondary, and tertiary controls for economic operation and the resilience of a DC microgrid. The simulation results verify that the proposed coordinated strategy is an effective way of ensuring the resilient response of DC microgrids to emergencies and optimizing their economic operation at steady state. The concept and prototype of a community (networked) microgrid that interconnecting multiple microgrids in a community are proposed. Two works are conducted. For the coordination, novel three-level hierarchical coordination strategy to coordinate the optimal power exchanges among neighboring microgrids is proposed. For the planning, a multi-microgrid interconnection planning framework using probabilistic minimal cut-set (MCS) based iterative methodology is proposed for enhancing the economic, resilience, and reliability signals in multi-microgrid operations. The implementation of high-reliability microgrids requires proper protection schemes that effectively function in both grid-connected and island modes. This chapter presents a communication-assisted four-level hierarchical protection strategy for highreliability microgrids, and tests the proposed protection strategy based on a loop structured microgrid. The simulation results demonstrate the proposed strategy to be an effective and efficient option for microgrid protection. Additionally, microgrid topology ought to be optimally planned. To address the microgrid topology planning, a graph-partitioning and integer-programming integrated methodology is proposed. This work is not included in the dissertation. Interested readers can refer to our related publication.
Ph.D. in Electrical and Computer Engineering, July 2015
Show less
POWER TAKE-OFF AND GRID SUPPORT IN HYBRID VEHICLES USING WOUND FIELD SYNCHRONOUS MACHINES
Title
POWER TAKE-OFF AND GRID SUPPORT IN HYBRID VEHICLES USING WOUND FIELD SYNCHRONOUS MACHINES
Creator
Dong, Weizhen
Date
2016, 2016-07
Description
Energy sectors are undergoing revolutionary changes. Due to environmental concerns and customer desires, a considerable increase of Electric...
Show moreEnergy sectors are undergoing revolutionary changes. Due to environmental concerns and customer desires, a considerable increase of Electric Vehicles (EVs) and Plug-in Hybrid Electric Vehicles (PHEVs) is expected. A technology of Vehicle to Grid (V2G) is emerging in the electric power industry. This technology provides connections between PHEVs and microgrids, and utilize PHEVs as distributed generators for grid support or as backup power sources. With the development of Electric Vehicles, wound field synchronous machines (WFSM) have been used and studied in EV traction motors and generators. For the application of EV technology, WFSMs have several advantages over permanent magnet synchronous machines (IPMSM) and induction machines (IM) including the complete control of the field excitation from the rotor side, higher system and machine efficiencies, and reduced cost due to the absence of rare earth permanent magnets. At the same time, WFSMs can work as generators to realize power take-off and microgrid support for EV tractions. Due to the several advantages of WFSMs in EVs application, this research focuses on the control of the WFSM in PHEVs for power take-off and grid support as a generator. PHEVs internal combustion (IC) engine is considered as a prime mover and would couple to the shaft which is connected to the WFSM. Such PHEVs applications would be used as power supplies for nearby loads and microgrids. This system is able to reduce cost of power electronics converters and directly provides desired AC voltage. This work aims to study the power take-off from hybrid electric vehicles using wound field synchronous machines and operation in microgrids. The feasible HEVs configurations to realize this purpose is studied. The modeling of IC engine, wound field synchronous machine, brushless exciter and distributed generators (DGs) in microgrid is demonstrated. One disadvantage of this application is the time delay during the combustion progress in the IC engine. This delay could affect the stability and dynamic response of the system. At the same time, the IC engine based generators have slower dynamic response compared with power electronic based sources. A state variable voltage regulator and a rotor speed controller are designed to improve the performance of the system. These controllers enable wound field synchronous machines provide desired voltage frequency and voltage magnitude. A real power - frequency droop controller and a reactive power – voltage droop controller are also studied. The droop controllers would keep the stability and better power quality of the system for islanded mode operation and grid-connected mode operation. The droop controllers enable EVs system share loads in a desire portion of power with other DGs in the grid and this reactive power – voltage droop controller would eliminate the circulating reactive power in the whole grid system. The EV’s isolated power take-off operation, islanded mode operation in microgrid with other DGs, and grid connected mode operation in microgrid are discussed. Stabilities, disturbance responses, and load sharing abilities are shown in simulation studies. The results are presented and discussed.
M.S. in Electrical Engineering, July 2016
Show less