Dynamic Studies of Multiterminal DC-AC Systems

In transient stability programs that use a static dc network representation, the procedure to determine the control mode of operation and the solution of the multiterminal dc system is complex and time consuming. A systematic approach that is based on a linear programming formulation is presented in this thesis. The constraints incorporated in the LB formulation automatically ensure that the solution obtained is feasible. It is shown that the method is not only computationally efficient but also versatile in its ability to handle many of the common control characteristics, such as those of the constant angle (extinction and ignition), constant voltage, constant power and current controls, voltage dependent current order limiter (VDCOL), end-stops, and also simulate the dynamics of power modulation and restart. As some applications require a three-phase detailed representation of the ac/dc system, a technique for detailed simulation of the dc converter and controls is also presented. The developed dynamic simulation program is used to investigate the problem of on-line network flow control using converter controls of a multiterminal dc system. In view of fast response of the dc powers to converter controls, a control method is proposed that extends the application of ac network flow control to dynamic situations. Possible applications of the method are to regulate power flows in a select group of ac lines, to smoothly steer the ac/dc system from its present state to some desired state and to enhance the dynamic performance of the ac system by controlling the transient changes in key or ’’backbone” ac lines

Real-time interactive speech technology at Threshold Technology, Incorporated

Basic real-time isolated-word recognition techniques are reviewed. Industrial applications of voice technology are described in chronological order of their development. Future research efforts are also discussed

Testing Considerations for Line Current Differential Schemes

Abstract-Testing line current differential (87L) schemes is more complicated than testing directional comparison schemes. The latter exchange simple on/off (permission or block) signals that can be conveniently checked at the output of a given relay and conveniently forced at the input to a given relay in the scheme. Line current differential schemes exchange synchronized current values that cannot be easily intercepted or forced at the 87L communications port of the relay. Moreover, the communications channel is an integral part of the 87L scheme, and its characteristic can impact some fundamental aspects of the scheme, such as sensitivity and speed. Therefore, it is preferable that the actual channel be in use when testing the scheme. Line current differential schemes that apply external time sources for synchronization need to be tested with time sources as well. Often, 87L schemes are tested with multiple crews dispatched to two or more line terminals using either test sets synchronized via the Global Positioning System or other methods of controlling the relationship and timing between current sources at the line terminals. This paper presents several approaches to testing 87L schemes. These approaches include verification of relay hardware, firmware and settings, channel performance, and, if used, external time sources. The paper also describes features of line current differential relays and multiplexers to aid testing

A Signal Segmentation Approach to Identify Incident/Reflected Traveling-Waves for Fault Location in Half-Bridge MMC-HVDC Grids

This article presents a new systematic technique for identifying voltage traveling-waves (TWs) to determine the location of line faults in half-bridge modular multilevel converter-based high-voltage direct-current (HBMMC-HVDC) grids. In this technique, the buffered voltage signal frame around the fault-detection time is first scaled and then segmented via an optimization process. Finally, the incident/reflected TWs arrival times are obtained by executing a simple search algorithm on the reconstructed signal segments’ differences. This article describes how to use this technique in three forms of TW-based fault location schemes, including the single-ended scheme with known TW velocity, the double-ended scheme with known TW velocity, and the double-ended scheme with unknown TW velocity. The application results on a 4-terminal HBMMC-HVDC grid simulated with exact component models show the proposed technique’s high capability and accuracy in all the three TW-based fault-location schemes. According to these results, the average fault-location errors are less than 0.5% for all the schemes. The numerical results also confirm that the proposed technique maintains its excellent performance, even in the face of close to terminal faults with distances down to 4 km, faults with high resistances up to 450 Ω, and noisy signals with signal-to-noise ratios down to 55 dB. Moreover, the comparison results confirm that the proposed approach is more tolerant of measurement noise than the wavelet transform.©2021 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.fi=vertaisarvioitu|en=peerReviewed

MULTIDIMENSIONAL OPTIMAL DROOP CONTROL FOR WIND RESOURCES IN DC MICROGRIDS

Two important and upcoming technologies, microgrids and electricity generation from wind resources, are increasingly being combined. Various control strategies can be implemented, and droop control provides a simple option without requiring communication between microgrid components. Eliminating the single source of potential failure around the communication system is especially important in remote, islanded microgrids, which are considered in this work. However, traditional droop control does not allow the microgrid to utilize much of the power available from the wind. This dissertation presents a novel droop control strategy, which implements a droop surface in higher dimension than the traditional strategy. The droop control relationship then depends on two variables: the dc microgrid bus voltage, and the wind speed at the current time. An approach for optimizing this droop control surface in order to meet a given objective, for example utilizing all of the power available from a wind resource, is proposed and demonstrated. Various cases are used to test the proposed optimal high dimension droop control method, and demonstrate its function. First, the use of linear multidimensional droop control without optimization is demonstrated through simulation. Next, an optimal high dimension droop control surface is implemented with a simple dc microgrid containing two sources and one load. Various cases for changing load and wind speed are investigated using simulation and hardware-in-the-loop techniques. Optimal multidimensional droop control is demonstrated with a wind resource in a full dc microgrid example, containing an energy storage device as well as multiple sources and loads. Finally, the optimal high dimension droop control method is applied with a solar resource, and using a load model developed for a military patrol base application. The operation of the proposed control is again investigated using simulation and hardware-in-the-loop techniques

Microprocessor control of converters for direct current transmission

Imperial Users onl

A survey of an introduction to fault diagnosis algorithms

This report surveys the field of diagnosis and introduces some of the key algorithms and heuristics currently in use. Fault diagnosis is an important and a rapidly growing discipline. This is important in the design of self-repairable computers because the present diagnosis resolution of its fault-tolerant computer is limited to a functional unit or processor. Better resolution is necessary before failed units can become partially reuseable. The approach that holds the greatest promise is that of resident microdiagnostics; however, that presupposes a microprogrammable architecture for the computer being self-diagnosed. The presentation is tutorial and contains examples. An extensive bibliography of some 220 entries is included

HVDC Systems Fault Analysis Using Various Signal Processing Techniques

The detection and fast clearance of faults are important for the safe and optimal operation of HVDC systems. In HVDC systems, various types of AC faults (rectifier & inverter side) and DC faults can occur. It is therefore necessary to detect the faults and classify them for better protection and diagnostics purposes. Various techniques for fault detection and classification in HVDC systems using signal processing techniques are presented and investigated in this research work. In this research work, it is shown that the wavelet transformation can effectively detect abrupt changes in system signals which are indicative of a fault. This research has focused on DC faults at various distances along the lines and AC faults on the converter side. The DC line current is chosen as the input to the wavelet transform. The 5th level coefficients have been used to identify the various faults in the LCC-HVDC system. Moreover, the value of these coefficients has been used for the classification of the different faults. For more accurate classification of faults, the wavelet entropy principle is proposed. In LCC-HVDC systems, a different approach for fault identification and classification is proposed. In this investigation an algorithm is developed that provides the trade-off between large input data size and minimal number of neurons in the hidden layer, without compromising the accuracy. The claim is confirmed by the results provided from the investigation for various fault conditions and its corresponding ANN output which confirms the specific fault detection and its classification. A fault identification and classification strategy based on fuzzy logic for VSC–HVDC systems is proposed. Initially, the developed Fuzzy Inference Engine (FIE) detects AC faults occurring in the rectifier side and DC faults on the cable successfully. However, it could not identify the line on which the fault has occurred. Hence, to classify the faults occurring in either AC section or DC section of the HVDC system, the FIE has to be restructured with appropriate data input. Therefore, a FIE which identifies different types of fault and the corresponding line where the fault occurs anywhere in the HVDC system was developed. Initially the developed FIE with three input and seven output parameters results in an accuracy level of 99.47% being achieved. After a modified FIE was developed with five inputs and seven output parameters, 21 types of faults in the VSC HVDC system were successfully classified with 100% accuracy. The FIE was further developed to successfully classify with 100% accuracy faults in Multi-Terminal HVDC systems

Design, Fabrication, and Characterization of Conjugated Polymeric Electrochemical Memristors as Neuromorphic/Integrated Circuits

Organic materials are promising candidates for future electronic devices compared to the complementing inorganic materials due to their ease of processability, use, and disposal, low cost of fabrication, energy efficiency, and flexible nature toward implementation as flexible and non-conformal devices.With that in mind, electrochemical materials have been widely demonstrated with commercial use as sensors, displays, and a variety of other electronic devices. As Moore\u27s law predicts the increase in the density of transistors on a chip, the requirement to create either smaller transistors or the replacement of the transistor device entirely is apparent. Memory resistors, coined ``memristor , are variable resistive tuning devices that are capable of information processing and data storage in one device. This work focuses on the embodiment of a non-volatile conjugated polymeric electrochemical memristor. Three-terminal memristive systems are fabricated and studied using various electrochemicals (a self-doped PEDOT derivative, a polypyrrole, and a dithienopyrrole derivative) and are tested for their electronic properties and biomimicking capabilities. Optical absorbance properties are studied in order to verify the electrochemical material\u27s redox tuning potential for their respective oxidized and reduced chemical forms. The three-terminal device employed a post-synaptic ``read\u27\u27 channel where conductivity of the electrochemical material was equated to synaptic weight and was electronically decoupled from the pre-synaptic programming electrode by means of a polymeric gel electrolyte. Basic electronic characteristics are exhibited for these three devices such as state stability and retention, non-volatile voltage-driven conductivity tuning, input parameter characteristic trends, and power consumption per input program. Biological synapses consume, on the order of, 1 - 100 fJ of energy per synaptic energy. The electrochemical materials used in this study, at their most optimized input parameters, were capable of demonstrating a 4.16 fJ/mm2 power consumption per input pulse and lead to a promising candidate for implementation as future artificial neural networks. Biological mimicry was displayed for these devices in the form of paired-pulse facilitation and paired-pulse depression, both a form of short term memory which observes the effect the timescale between two incoming inputs has on the change in the final output signal. Toward the indication for the replacement of transistors with three-terminal memristors, basic circuit operations are achieved and demonstrated for these devices. These operations include both Boolean and elementary algebra, key features that demonstrate data processing and storage in-memory where the physical states of the conjugated polymer film represent either logical statements or arithmetic counting variables. The Boolean algebra demonstrated the use of a single memristive device equal to a variety of single logic gates (AND, NAND, OR and NOR) where, by wiring several devices in series, more advanced combinational logic gates can be achieved. Furthermore, each device was capable of displaying elementary algebra for the basic arithmetic functions of addition, subtraction, multiplication, and division. In regards to thin film deposition techniques, the self-doped PEDOT device employed roll-to-roll gravure printing, a high speed and high resolution commercially used deposition technique. The polypyrrole device was fabricated implementing an in-situ polymerization technique, referred to as vapor phase polymerization, and demonstrated the use of this technique toward non-conformal devices. The dithienopyrrole derivative was polymerized through the same vapor phase polymerization technique as the polypyrrole and used in tandem with screen printing in order to construct the final device, including the oxidant film, the silver electrodes, and the polymeric gel electrolyte