Computational approaches for voltage stability monitoring and control in power systems

The electric power grid is a complex, non-linear, non-stationary system comprising of thousands of components such as generators, transformers, transmission lines and advanced power electronics based control devices, and customer loads. The complexity of the grid has been further increased by the introduction of smart grid technologies. Smart grid technology adds to the traditional power grids advanced methods of communication, computation and control as well as increased use of renewable energy sources such as wind and solar farms and a higher penetration of plug-in electric vehicles among others. The smart grid has resulted in much more distributed generation, bi-directional powerflows between customers and the grid, and the semi-autonomous control of subsystems. Due to this added complexity of the grid and the need to maintain reliable, quality, efficient, economical, and environmentally friendly power supply, advanced monitoring and control technologies are needed for real-time operation of various systems that integrate into the transmission and distribution network. In this dissertation, the development of computational intelligence methods for on-line monitoring of voltage stability in a power system is presented. In order to carry out on-line assessment of voltage stability, data from Phasor Measurement Units (PMUs) is utilized. An intelligent algorithm for optimal location of PMUs for voltage stability monitoring is developed. PMU information is used for estimation of voltage stability load index in a power system with plug-in electric vehicle and wind farm included. The estimated voltage stability index is applied in the development of an adaptive dynamic programming based optimal secondary voltage controller to coordinate the reactive power capability of two FACTS devices --Abstract, page iii

Application of advanced technology to space automation

Automated operations in space provide the key to optimized mission design and data acquisition at minimum cost for the future. The results of this study strongly accentuate this statement and should provide further incentive for immediate development of specific automtion technology as defined herein. Essential automation technology requirements were identified for future programs. The study was undertaken to address the future role of automation in the space program, the potential benefits to be derived, and the technology efforts that should be directed toward obtaining these benefits

A survey on voltage stability indices for power system transmission and distribution systems

Voltage stability is a critical aspect of power system operation, ensuring the reliable and efficient delivery of electrical energy to consumers. Recently, voltage stability in the power system has received much attention. The primary cause of voltage instability is the lack of real and reactive power generation to cope with the continuous demand increment. Maintaining voltage stability while planning, controlling, and assessing the system’s security is a difficult task for power system engineers. From knowledge of past incidents, a lack of reactive power is identified as the primary cause of voltage instability, which may further lead to the total collapse of the system. The importance of voltage stability assessment is essential to maintain the integrity of power systems. It helps prevent voltage instability, which can lead to cascading failures and widespread outages. This paper uses various parameters, including load demand, generator capacity, and system impedance, to develop voltage stability indices (VSIs). The paper mainly focuses on the idea of VSIs that have been developed in order to monitor and control the criticality of the power system. The voltage stability indices for transmission and distributed systems, as well as their subclasses, are thoroughly reviewed in this study. Furthermore, traditional voltage stability methods, as well as various software tools for monitoring the voltage stability problems, are also discussed. In addition, the development of VSIs and its related concepts are clearly described in this paper. This comprehensive survey provides a decent groundwork for future work in this area, and assists professionals in selecting the optimal VSI for various applications. Moreover, it provides a concise overview of methods and the importance of voltage stability assessment in both transmission and distribution systems

Towards Very Large Scale Analog (VLSA): Synthesizable Frequency Generation Circuits.

Driven by advancement in integrated circuit design and fabrication technologies, electronic systems have become ubiquitous. This has been enabled powerful digital design tools that continue to shrink the design cost, time-to-market, and the size of digital circuits. Similarly, the manufacturing cost has been constantly declining for the last four decades due to CMOS scaling. However, analog systems have struggled to keep up with the unprecedented scaling of digital circuits. Even today, the majority of the analog circuit blocks are custom designed, do not scale well, and require long design cycles. This thesis analyzes the factors responsible for the slow scaling of analog blocks, and presents a new design methodology that bridges the gap between traditional custom analog design and the modern digital design. The proposed methodology is utilized in implementation of the frequency generation circuits – traditionally considered analog systems. Prototypes covering two different applications were implemented. The first synthesized all-digital phase-locked loop was designed for 400-460 MHz MedRadio applications and was fabricated in a 65 nm CMOS process. The second prototype is an ultra-low power, near-threshold 187-500 kHz clock generator for energy harvesting/autonomous applications. Finally, a digitally-controlled oscillator frequency resolution enhancement technique is presented which allows reduction of quantization noise in ADPLLs without introducing spurs.PhDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/109027/1/mufaisal_1.pd

Security aspects of SCADA and DCS environments

Abstract SCADA Systems can be seen as a fundamental component in Critical Infrastructures, having an impact in the overall performance of other Critical Infrastructures interconnected. Currently, these systems include in their network designs different types of Information and Communication Technology systems (such as the Internet and wireless technologies), not only to modernize operational processes but also to ensure automation and real-time control. Nonetheless, the use of these new technologies will bring new security challenges, which will have a significant impact on both the business process and home users. Therefore, the main purpose of this Chapter is to address these issues and to analyze the interdependencies of Process Control Systems with ICT systems, to discuss some security aspects and to offer some possible solutions and recommendations

Voltage and Timing Adaptation for Variation and Aging Tolerance in Nanometer VLSI Circuits

Process variations and circuit aging continue to be main challenges to the power-efficiency of VLSI circuits, as considerable power budget must be allocated at design time to mitigate timing variations. Modern designs incorporate adaptive techniques for variation compensation to reduce the extra power consumption. The efficiency of existing adaptive approaches, however, is often significantly attenuated by the fine-grained nature of variations in nanometer technology such as random dopant fluctuation, litho-variation, and different rates of transistor degradation due to non-uniform activity factors. This dissertation addresses the limitations from existing adaptation techniques, and proposes new adaptive approaches to effectively compensate the fine-grained variations. Adaptive supply voltage (ASV) is one of the effective adaptation approaches for power-performance tuning. ASV has advantages on controlling dynamic and leakage power, while voltage generation and delivery overheads from conventional ASV systems make their application to mitigate fine-grained variations demanding. This dissertation presents a dual-level ASV system which provides ASV at both coarse-grained and fine-grained level, and has limited power routing overhead. Significant power reduction from our dual-ASV system demonstrates its superiority over existing approaches. Another novel technique on supply voltage adaptation for variation resilience in VLSI interconnects is proposed. A programmable boostable repeater design boosts switching speed by raising its internal voltage rail transiently and autonomously, and achieves fine-grained voltage adaptation without stand-alone voltage regulators or additional power grid. Since interconnect is a widely recognized bottleneck to chip performance and tremendous repeaters are employed on chip designs, boostable repeater has plenty of chances to improve system robustness. A low cost scheme for delay variation detection is essential to compose an efficient adaptation system. This dissertation presents an area-efficient built-in delay testing scheme which exploits BIST SCAN architecture and dynamic clock skew control. Using this built-in delay testing scheme, a fine-grained adaptation system composed of the proposed boostable repeater design and adaptive clock skew control is proposed, and demonstrated to mitigate process variation and aging induced timing degradations in a power as well as area efficient manner

A CAD tool for the prediction of VLSI interconnect reliability.

Thesis (Ph.D.)-University of Natal, Durban, 1988.This thesis proposes a new approach to the design of reliable VLSI interconnects, based on predictive failure models embedded in a software tool for reliability analysis. A method for predicting the failure rate of complex integrated circuit interconnects subject to electromigration, is presented. This method is based on the principle of fracturing an interconnect pattern into a number of statistically independent conductor segments. Five commonly-occurring segment types are identified: straight runs, steps resulting from a discontinuity in the wafer surface, contact windows, vias and bonding pads. The relationship between median time-to-failure (Mtf) of each segment and physical dimensions, temperature and current density are determined. This model includes the effect of time-varying current density. The standard deviation of lifetime is also determined as a function of dimensions. A· minimum order statistical method is used to compute the failure rate of the interconnect system. This method, which is applicable to current densities below 106 AI cm2 , combines mask layout and simulation data from the design data base with process data to calculate failure rates. A suite of software tools called Reliant (RELIability Analyzer for iNTerconnects) which implements the algorithms described above, is presented. Reliant fractures a conductor pattern into segments and extracts electrical equivalent circuits for each segment. The equivalent circuits are used in conjunction with a modified version of the SPICE circuit simulator to determine the currents in all segments and to compute reliability. An interface to a data base query system provides the capability to access reliability data interactively. The performance of Reliant is evaluated, based on two CMOS standard cell layouts. Test structures for the calibration of the reliability models are provided. Reliant is suitable for the analysis of leaf cells containing a few hundred transistors. For MOS VLSI circuits, an alternative approach based on the use of an event-driven switch-level simulator is presented

Center for Space Microelectronics Technology 1988-1989 technical report

The 1988 to 1989 Technical Report of the JPL Center for Space Microelectronics Technology summarizes the technical accomplishments, publications, presentations, and patents of the center. Listed are 321 publications, 282 presentations, and 140 new technology reports and patents

Optimal Transmission Switching in Power Systems with Large-scale Renewable Resources

In the past decade, there has been a rapid growth for renewable generations in power systems worldwide. However, the natural intermittency of wind and solar causes a variable output for renewable generations in power systems. Under this new situation, the optimal network topology of a power system can vary with time. This research focuses on an emerging topology control technology, optimal transmission switching, to improve the flexibility and efficiency of power systems with large-scale renewable generations. Novel optimization and stability enhancement approaches for optimal transmission switching are developed considering the grid uncertainties caused by the highly variable renewable generations and load fluctuation. Three major problems of optimal transmission switching are resolved in this research. First, novel optimization approaches are developed to calculate accurate switching plans for optimal transmission switching actions. Different from the existing approaches, the proposed approaches are focused on the alternating current optimal power flow for a better accuracy. New elements like renewable generations and energy storage devices are included in the optimization problems. In addition, grid uncertainties are taken into consideration and stochastic programming is used in the decision-making process. A scalable decomposition approach is proposed to solve the stochastic programming problem of the alternating current optimal power flow based optimal transmission switching. Second, transient stability issues in the transmission switching actions are investigated and transient stability enhancement methods are proposed. And a new transient stability index, critical switching flow, is proposed for transmission switching actions. Based on the new quantitative index, a preventive stabilizing redispatch scheme is developed. The proposed scheme considers the grid uncertainties in the day-ahead planning and can be applied to avoid unstable switching actions in the online operation. Third, the cyber-security issues associated with transmission switching actions are analyzed. The potential threat of false data injection attack is discussed. The cyber-attack may compromise the state estimator and make a risky switching action stable in the online stability check. As a result, a catastrophic instability will be led by the cyber-attack. The countermeasure is given to defend the cyber-attack. Numerical results on the different test systems justify the proposed approaches in this research. The developed approaches will facilitate the implementation of optimal transmission switching in the real world

Advanced control system for stand-alone diesel engine driven-permanent magnetic generator sets

The main focus is on the development of an advanced control system for variable speed standalone diesel engine driven generator systems. An extensive literature survey reviews the historical development and previous relevant research work in the fields of diesel engines, electrical machines, power electronic converters, power and electronic systems. Models are developed for each subsystem from mathematical derivations with necessary simplifications made to reduce complexity while retaining the required accuracy. Initially system performance is investigated using simulation models in Matlab/Simulink. The AC/DC/AC power electronic conversion system used employs a voltage controlled dc link. The ac voltage is maintained at constant magnitude and frequency by using a dc-dc converter and a fixed modulation ratio VSI PWM inverter. The DC chopper provides fast control of the output voltage by dealing efficiently with transient conditions. A Variable Speed Fuzzy Logic Core (VSFLC) controller is combined with a classical control method to produce a novel hybrid controller. This provides an innovative variable speed control that responds to both load and speed changes. A new power balance based control strategy is proposed and implemented in the speed controller. Subsequently a novel overall control strategy is proposed to co-ordinate the hybrid variable speed controller and chopper controller to provide overall control for both fast and slow variations of system operating conditions. The control system is developed and implemented in hardware using Xilinx Foundation Express. The VHDL code for the complete control system design is developed and the designs are synthesised and analysed within the Xilinx environment. The controllers are implemented with XC95108-PC84 and XC4010-PC84 to provide a compact and cheap control system. A prototype experimental system is described and test results are obtained that show the combined control strategy to be very effective. The research work makes contributions in the areas of automatic control systems for diesel engine generator sets and CPLD/FPGA application that will benefit manufacturers and consumers.EPSR