Field Programmable Analog Arrays for Conditioning Ultrasonic Sensors

This paper proposes the use of field programmable analog arrays (FPAAs) as adaptive conditioning blocks for ultrasonic sensors. The uncertainty achievable through this technique, in fact, results very sensitive to the measurement conditions, due to the attenuation affecting the echo during its propagation. Indeed, FPAAs emulate analog circuits whose characteristics have to be dynamically tuned according to different operating conditions. Actually, the signal provided by the ultrasonic sensor is properly processed in order to improve the overall measurement accuracy. In this paper, the prototype of a distance meter based on time-of-flight (TOF) measurement is presented in order to evidence the advantages gained by FPAA features in processing the sensor output to compensate echo attenuation and distortion versus target distance. The prototype working is supervised by a digital signal controller (DSC) whose tasks are: 1) driving the ultrasonic transducer; 2) performing the echo acquisition; 3) tuning on the fly the FPAA features; 4) evaluating the TOF; 5) measuring the target distance; and 6) delivering the final result to the end user. This paper is completed by the results achieved in a number of experimental tests allowing interesting considerations to be drawn. In particular, the experiments confirm the prototype reliability and effectiveness also with ultrasonic echoes characterized by very low signal-to-noise ratios.     

High-speed electromechanical digital voltmeter

Conclusions A method for raising the operating speed of dc digital voltmeters using contact elements is suggested and a schematic for a high-speed digital voltmeter supplied.The peculiarities of the above instrument consist of combining the relaxation relays (dc amplitude analyzers) with the compensating part of the voltmeter and in a special circuit for eliminating the possibility of an incorrect operation of a relay.If the required elements are added to the above circuit it is possible to make a multirange voltmeter with an automatic inducation of the polarity of the measured voltage. Difficulties may arise in adjusting the relaxation relays to low voltage operating levels. In this case the circuit may be supplemented by an additional amplifier with a gain of 10, and a negative feedback large enough to make the total effect of the zero drift and gain instability smaller than the minimum calibration of the instrument.     

Determination of preventive maintenance periodicities of standby devices

This article presents a statistical approach of analysis and decision that uses reliability techniques to define the best periodicity for preventive maintenance of power system protective relays. Relays are standby devices and may stay in the hidden failure state when they are not working. This state of failure generates difficulties in the determination of preventive maintenance periodicities. A case study presented in this work deals specifically with the reliability of the transmission and distribution system protective relays of CEMIG (the state owned Electrical Power Company of Minas Gerais, Brazil). Preventive maintenance data of protective relays obtained during a 4-year period were used in the proposed method. The choice of the periodicities, distinguished by groups of similar relay and voltage operation levels of the protected systems, is made according to the failure risk level that the company is willing to take. The main result obtained by using this method is a substantial reduction of 62% in the amount of preventive maintenance work load for the relays of the distribution system.     

Software reliability allocation of digital relay for transmission line protection using a combined system hierarchy and fault tree approach

Digital relay is a special purpose signal processing unit in which the samples of physical parameters such as current, voltage and other quantities are taken. With the proliferation of computer technology in terms of computational ability as well as reliability, computers are being used for such digital signal processing purposes. As far as computer hardware is concerned, it has been growing steadily in terms of power and reliability. Since power plant technology is now globally switching over to such computer-based relaying, software reliability naturally emerges as an area of prime importance. Recently, some computer-based digital relay algorithms have been proposed based on frequency-domain analysis using wavelet-neuro-fuzzy techniques for transmission line faults. A software reliability allocation scheme is devised for the performance evaluation of a multi-functional, multi-user digital relay that does detection, classification and location of transmission line faults.     

Joint power allocation and relay positioning in multi-relay cooperative systems

The authors consider a dual-hop multi-relay cooperative relay system in this study. Both decode-and-forward (DF) and amplify-and-forward (AF) protocols are considered. Under different relay selection strategies, the authors derive closed-form outage probability expressions. With the second-order channel statistics, the authors propose to jointly optimise power allocation (PA) and relay positions in order to minimise the system outage probability. Simulation results show that the proposed adaptive allocation algorithms significantly outperform fixed allocation algorithms. With the proposed joint optimisation algorithm, AF relaying outperforms DF relaying when multiple relays are selected to help. When only the best relay is selected to help, DF relaying is shown to have better performance.     

A methodology to perform online self-testing for field-programmable analog array circuits

This paper presents a methodology to perform online self-testing for analog circuits implemented on field-programmable analog arrays (FPAAs). It proposes to partition the FPAA circuit under test into subcircuits. Each subcircuit is tested by replicating the subcircuit with programmable resources on the FPAA chip, and comparing the outputs of the subcircuit and its replication. To effectively implement the proposed methodology, this paper proposes a simple circuit partition method and develops techniques to address circuit stability problems that are often encountered in the proposed testing method. Furthermore, error sources in the proposed testing circuit are studied and methods to improve the accuracy of testing results are presented. Finally, experimental results are presented to demonstrate the validity of the proposed methodology.     

Fast and secure breaker failure detection algorithms

In a power system, every apparatus is equipped with a primary protection to detect faults and isolate the equipment by opening the circuit breaker. Breaker failure (BF) protection is employed as a means of local backup protection to detect failure of a circuit breaker. In this research work, a critical challenge facing numerical BF relays namely longer reset time of current based BF algorithms is examined by means of simulations and realistic experiments. Two new fast resetting algorithms for BF protection with reset time of less than half a power system cycle are proposed as means of enhancing BF protection. Simulations and experiments reflecting realistic conditions were used for performance evaluation of the enhanced BF algorithms. The proposed algorithms have a reset time of around half a cycle compared to 2?3 cycles in the case of a commercial numerical BF relay selected. Results indicate that the new algorithms significantly enhance the numerical BF protection.     

New achievable rate and a certain capacity result for a stochastic two relay network with no interference

Gastpar and Vetterli named the ad hoc networks with one randomly selected source-destination pair as relay networks, and they suggested using arbitrary network coding in order to increase the overall efficiency. Here, the relay network is investigated with two relays, no interference and a new achievable rate is obtained using a new network coding (decode-and-broadcast). The obtained achievable rate (i) gives the lower bound for general relay channel, obtained by Cover and El Gamal, but with a slight difference owing to no interference assumption at the receiver, (ii) includes the one relay rates of a two-level relay channel studied by Gupta and Kumar using point-to-point coding, (iii) includes the rates of two-relay Aref network and other special two-relay networks, (iv) meets the max-flow min-cut upper bound under certain additional assumptions resulting in certain capacity theorems that include the related previous capacities, (v) is validated by its consistency with previous results relevant to special cases of broadcast channels.     

Characteristics of voltage relays for embedded synchronous generators protection

Here, a comprehensive characterisation of the performance of voltage relays, focusing on their capability to detect islanding of embedded synchronous generators is presented. Such characterisation is done by using the performance curves and the concept of critical reactive power imbalance, which allows a systematic analysis of voltage relays considering a wide range of system operating points. The impacts of important factors on the relay performance are evaluated, such as the presence of voltage-dependent loads and the generator exciter control mode. Moreover, a graphical approach that allows protection engineers to adjust voltage relays to reach two objectives simultaneously: (i) to be sensitive enough to detect islanding efficiently and (ii) to satisfy the protection requirements against abnormal voltage variation is proposed. Results can be quite attractive to understand voltage relays behaviour and limitations and thus, they can be adjusted more efficiently     

Comprehensive partial decoding approach for two-level relay networks

Partial decoding scheme is a scheme in which each relay decodes only part of the transmitted message. Obviously, the achievable rates proposed by the partial decoding scheme subsume the achievable rates proposed by the full decoding scheme. The other motivation of using partial decoding scheme is that there are some special classes of relay networks such as semi-deterministic and orthogonal relay networks such that their capacities are obtained via this scheme. The authors propose a comprehensive partial decoding scheme based on regular encoding/sliding window decoding analysis to propose a new achievable rate for two-level relay networks. In contrast with the previously proposed methods, here the authors consider all possible partial decoding states that can occur between the different parts of the messages of the source and the relays in a two-level relay network. In this way, the common and private parts of the message transmitted by the source are defined to be decoded by the appropriate relays. Moreover, in the proof, the authors take advantage of regular encoding/sliding window decoding scheme that has superiorities to regular encoding/backward decoding and irregular encoding/random partitioning, in having less delay and yielding higher rates, respectively.     

Time-Synchronized Ranging System

This paper describes a time-ordered precision ranging system, identified as time synchronized ranging system (TSRS). The TSRS is a cooperative ranging system serving up to 1024 users within an operational community. Synchronization of time, relative to a designated controller, is established and maintained to less than 7 ns. Slant range measurements between users and controller are provided with a measurement accuracy of 21 ft, one sigma for ranges up to 100 nmi. The synchronization and range-measurement process also provides a high speed, real time, two-way data link between members of the community including relay capabilities where required. Automatic unit identification is provided by means of user time slot assignments. Design features of interest include ultra-high-speed digital logic, digital filtering (Kalman) of time-error measurements with optimal correction of both frequency and phase of a 100-MHz precision source. The TSRS has been tested both in surface communities and surface-air communities and is currently under test by the U. S. Navy.     

基于FPGA设计的高帧频电视高速图象预处理器

针对高帧频电视系统的特点 ,应用现场可编程门阵列 (FPGA)构造高速图象预处理器 ,完成数字电视的自适应阈值的实时计算 ,进而实现高帧频电视系统全视场快速搜索与在线数字图象分割。仿真和实验结果证明是可行的。     

Out-of-step detection algorithm using frequency deviation of voltage

Protection against transient instability and a consequent out-of-step condition is a major concern for the utility industry. An unstable system may cause serious damage to system elements such as generators and transmission lines, therefore out-of-step detection is essential to operate a system safely. The traditional out-of-step relays detect out-of-step conditions by using distance relays and timers. However, such a relay monitors only apparent impedance which is an indirect function of generator angle, and the relay cannot cope with the out-of-step situation for the more severe instability situation of very fast power swings which can also cause damage to transmission lines if not detected fast enough, as is the case with conventional detection techniques. Digital filters based on discrete Fourier transforms are used to calculate the frequency of a sinusoidal voltage, and then the generator angle is estimated using the deviation of the calculated frequency component of the voltage. The proposed out-of-step detection algorithm is based on the assessment of transient stability using the equal-area criterion. It is verified and tested by using ATP/EMTP MODELS, and the simulation results show that the out-of-step conditions are detected accurately employing the proposed algorithm.     

New techniques for fast hybrid solutions of systems of equations

A fast analogue solver with limited precision is used as a preconditioner in an iterative process which develops full digital precision. This hybrid process is highly parallel, and, in principle, it can be faster than digital computations alone. A problematic feature of this process is that the low analogue precision can adversely affect convergence speed. New techniques are introduced to address this limitation. A partial separation of analogue imprecision and poor problem condition is made. Fully parallel digital (smoothing) iterations are introduced to eliminate the effect of random errors which accompany analogue–digital conversion. Application is made to the problem of repeated summation.     

Symmetric relaying based on partial decoding and the capacity of a class of relay networks

Symmetric relaying is a method of relaying in which the relays can decode the message of other relays in the network in addition to the source message. In this paper an achievable rate is presented for a symmetric two-relay network based on partial decoding. The strategy make use of familiar techniques such as product binning, regular encoding/sliding window decoding and regular encoding/backward decoding. The proposed rate is shown to subsume the previously proposed rate for feed-forward relay network based on decode-andforward. This rate is also used to establish the capacity of a generalisation of Aref network called `semideterministic relay network with no interference at the relays? and independent relay inputs.     

Deriving operating characteristic equations for overcurrent protection devices based on eigensystem realization algorithm

Accurate representation of the operating characteristics of conventional inverse-time overcurrent (OC) protection devices plays an important role in protection coordination schemes. Based on the singular value decomposition of the Hankel matrix, this study uses the eigensystem realization algorithm to curve-fit the characteristic curves of OC protection devices under the digital state-space model and obtain the equations of their operating characteristics. This study applies the proposed method to four types of OC protection devices, including two electromechanical OC relays, one digital OC relay, and one power fuse. One characteristic curve from each protection device is selected for curve-fitting. For all four OC protection devices, the absolute error values for the hundreds of sample points between the actual characteristic curves and the corresponding curve-fitting equations are all less than 10 ms. The numbers of fitting components required are determined by the desired maximum absolute values of errors for the fitting equation. Finally, this study uses the derived equation to construct the characteristic curve of customized OC relay to solve the coordination problem of power system protection.     

智能电力自动化综合保护器在空分中的应用

智能电力自动化综合保护器 ,是计算机智能数码技术及网络通讯技术与传统电力系统继电保护技术相结合的产品 ,具备优异的性能及强大的综合功能。针对性地介绍了几个空分项目中采用综合保护器进行设计的情况 ,使用效果令人满意     

Effect of substrate and metal layer deformation on recording characteristics of recordable discs with metallic thin film

Compact disc-recordable (CD-R) and digital versatile disc-recordable (DVD-R) discs were fabricated with a polycarbonate substrate, metallic thin film, organic buffer layer, reflective layer, and protective layer. Recording characteristics of a CD-R disc at various recording speeds, from 1x to 8x, were evaluated, and the deformation shapes of each layer after recording were investigated and compared with the DVD-R disc. The relationship between deformation and recording characteristics was studied and interpreted by numerical calculation. The modulated amplitude of recorded signals is increased as the recording speed increases, owing to the increase in decomposition of the buffer layer, which resulted from the localization of heat on the metallic thin film. On the basis of these results, a DVD-R disc with metallic thin film is expected to have better recording characteristics at a higher recording speed.     

Diversity analysis of smart relaying over Nakagami and Hoyt generalised fading channels

Signal transmission with the help of relay(s) in wireless networks can achieve spatial diversity without the need of having multiple attennas at the source and/or destination. Among various signal processing techniques proposed for the relays, the adaptive decode-and-forward (DF) relaying strategy, recently proposed by Wang et al. and generally referred to as smart relaying, has been shown to achieve the maximal spatial diversity even when imperfect detection is committed at the relays. The work by Wang et al., however, only considers Rayleigh fading channels. This paper extends the diversity analysis of the smart relaying technique to the important Nakagami and Hoyt generalised fading channels. Performance analysis proves that, at high signal-to-noise ratio, the maximal diversity order achieved by the smart relaying system under the Nakagami channel is m_SD + min{m_SR, m_RD}, where m_SR, m_RD and m_SD are the fading figures of the source?relay (S?R), relay?destination (R?D) and source?destination (S?D) links. Under the Hoyt fading channel, the diversity order is 2. The obtained results on the diversity order are shown to be insensitive to the quality of the R?D feedback channel.     

Parallel tsunami simulation and visualization on tiled display wall using OpenGL Shading Language

Tsunami simulation consists of fluid dynamics, numerical computations, and visualization techniques. Nonlinear shallow water equations are often used to model the tsunami propagation. Tsunami inundation is modeled by adding the friction slope to the conservation of momentum. The two-step second-order finite difference MacCormack numerical method can solve these equations. It is well suited for nonlinear equations and simpler for related application development. In addition, the finite difference method can be computed in parallel. The programmable graphics hardware allows general-purpose computing on graphics processing units (GPUs) to solve the MacCormack method in parallel to speed up the simulation. Tsunami simulation data can be loaded as textures data in graphics memory, the computation processes can be written as shader programs using OpenGL Shading Language so that the operations can be computed by graphics processors in parallel. We developed different versions of the tsunami simulation and visualization programs: (i) CPU-based, and (ii) CPU–GPU collaboration to implement the MacCormack numerical method. The performance results showed that graphics hardware accelerated simulation had a significant improvement in the execution time of each computation step. Real-time simulation and visualization are made possible by the programmable shaders. Furthermore, we achieved high-performance parallel visualization on a tiled display wall with a cluster of computers.