Showing papers on "Stuck-at fault published in 2015"

Reliability Improvement of a T-Type Three-Level Inverter With Fault-Tolerant Control Strategy

Abstract: This paper proposes a fault-tolerant control strategy for a T-type three-level inverter when an open-circuit fault occurs. The proposed method is explained by dividing fault into two cases: the faulty condition of half-bridge switches and neutral-point switches. In case of the open-circuit fault in a neutral-point switch, two methods will be proposed and compared based on thermal analysis and neutral-point voltage oscillation. The reliability of T-type inverter systems is improved considerably by the proposed algorithm when a switch fails. The proposed method does not require any additional components. Simulation and experimental results verify the validity and feasibility of the proposed fault-tolerant control strategy.

Adaptive Nonlinear Model-Based Fault Diagnosis of Li-Ion Batteries

Abstract: In this paper, an adaptive fault diagnosis technique is used in Li-ion batteries. The diagnosis process consists of multiple nonlinear models representing signature faults, such as overcharge and overdischarge, causing significant model parameter variation. The impedance spectroscopy of a Li-ion $(\hbox{LiFePO}_{4})$ cell is used, along with the equivalent circuit methodology, to construct nonlinear battery signature-fault models. Extended Kalman filters are utilized to estimate the terminal voltage of each model and to generate residual signals. The residual signals are used in the multiple-model adaptive estimation technique to generate probabilities that determine the signature faults. It can be seen that, by using this method, signature faults can be detected accurately, thus providing an effective way of diagnosing Li-ion battery failure.

Global Fault-Tolerant Control Technique for Multiphase Permanent-Magnet Machines

Abstract: In this paper, a global fault-tolerant control (FTC) technique is proposed for multiphase permanent-magnet (PM) machine drives. The goal of the proposed FTC is to find a general closed-form solution for healthy phase currents under steady-state postfault conditions. Healthy phase currents are found through an optimization problem to produce ripple-free output torque with minimum ohmic losses. A comprehensive FTC approach should be able to provide fault-tolerant currents for multiphase machines with any number of phases. In addition, it needs to find currents based on fault type (open-circuit/short-circuit), fault locations [phase(s) and/or line(s)], connection of stator windings, and even different control objectives. An important feature of the proposed method is its flexibility and simplicity in dealing with all possible fault conditions. The proposed method is a great tool to evaluate fault-tolerant capability of different drive systems in terms of maximum available ripple-free torque and copper losses. Due to its simplicity and flexibility, it is also well-suited for real-time implementation. A five-phase PM machine is used as an example to investigate the validity of the proposed solutions through finite-element analysis and experimental tests.

Speed and Current Sensor Fault Detection and Isolation Technique for Induction Motor Drive Using Axes Transformation

Abstract: This paper presents a new technique for fault detection and isolation to make the traditional vector-controlled induction motor (IM) drive fault tolerant against current and speed sensor failure. The proposed current estimation uses d- and q-axes currents and is independent of the switching states of the three-leg inverter. While the technique introduces a new concept of vector rotation to generate potential estimates of the currents, speed is estimated by one of the available model reference adaptive system (MRAS) based formulations. A logic-based decision mechanism selects the right estimate and reconfigures the system (by rejecting the signal from the faulty sensors). Such algorithm is suitable for different drives, including electric vehicles to avoid complete shutdown of the system, in case of sensor failure. The proposed method is extensively simulated in MATLAB/SIMULINK and experimentally validated through a dSPACE-1104-based laboratory prototype.

Current Residual Vector-Based Open-Switch Fault Diagnosis of Inverters in PMSM Drive Systems

Abstract: This paper presents an open-circuit (OC) fault diagnostic method of inverters in closed-loop controlled permanent magnet synchronous motor drive systems based on current residual vector (CRV). This method can get rid of effects of the load and the main controller to obtain reliable detection. The motor drive system is a hybrid system composed of discrete switching signal events and continuous current state variables, which evolves in certain law driven by discrete events. At the base of analyzing operation modes of the system, a mixed logical dynamic (MLD) model of the motor drive system is built to estimate motor currents. Consequently, the proposed fault diagnostic scheme is constructed by the healthy current estimator based on the MLD model in parallel with the plant. When an OC fault occurs, the CRV between the estimator and the plant will show featured amplitude and phase, and hence the fault can be detected. The method utilizes variables already used by the main controller, avoiding the use of extra sensors. During the implementation, amplitude threshold and phase sector are used in order to avoid effects of measurement errors, model parameter errors and noises, which improves the reliability and robustness. Simulation and experimental results validate the proposed diagnostic method, and the diagnostic duration can be reduced within a quarter of fundamental wave period.

Photovoltaic Systems Reliability Improvement by Real-Time FPGA-Based Switch Failure Diagnosis and Fault-Tolerant DC–DC Converter

Abstract: The increased penetration of photovoltaic (PV) systems in different applications with critical loads such as in medical applications, industrial control systems, and telecommunications has highlighted pressing needs to address reliability and service continuity. Recently, distributed maximum power point tracking architectures, based on dc–dc converters, are being used increasingly in PV systems. Nevertheless, dc–dc converters are one of the important failure sources in a PV system. Since the semiconductor switches are one of the most critical elements in these converters, a fast switch fault detection method (FDM) is a mandatory step to guarantee the service continuity of these systems. This paper proposes a very fast FDM based on the shape of the inductor current associated to fault-tolerant (FT) operation for boost converter used in PV systems. By implementing fault diagnosis and reconfiguration strategies on a single field-programmable gate array target, both types of switch failure (open- and short-circuit faults) can be detected, identified and handled in real time. The FDM uses the signal provided by the current sensor dedicated to the control of the system. Consequently, no additional sensor is required. The proposed FT topology is based on a redundant switch. The results of hardware-in-the-loop and experimental tests, which all confirm the excellent performances of the proposed approach, are presented and discussed. The obtained results show that a switch fault can be detected in less than one switching period, typically around 100 ms in medium power applications, by the proposed FDM.

Fault Estimation and Fault-Tolerant Control for Discrete-Time Dynamic Systems

Abstract: In this paper, a novel discrete-time estimator is proposed, which is employed for simultaneous estimation of system states, and actuator/sensor faults in a discrete-time dynamic system. The existence of the discrete-time simultaneous estimator is proven mathematically. The systematic design procedure for the derivative and proportional observer gains is addressed, enabling the estimation error dynamics to be internally proper and stable, and robust against the effects from the process disturbances, measurement noise, and faults. Based on the estimated fault signals and system states, a discrete-time fault-tolerant design approach is addressed, by which the system may recover the system performance when actuator/sensor faults occur. Finally, the proposed integrated discrete-time fault estimation and fault-tolerant control technique is applied to the vehicle lateral dynamics, which demonstrates the effectiveness of the developed techniques.

Fault-Location Scheme for Power Distribution System with Distributed Generation

Abstract: This paper presents a novel fault-location scheme for unbalanced power distribution system in the presence of distributed generation (DG). The proposed scheme first identifies the possible fault locations using a new formulation of the impedance-based method. The new formulation overcomes the requirement of fault-type identification by using only one fault-location equation. The proposed equation is applicable to all shunt fault types. From the possible fault locations, the exact fault location is then identified by matching the measured voltage at the substation bus and each DG unit bus with calculated ones. The proposed scheme is applicable for all DG types without the need for their individual parameters. The balanced and unbalanced laterals and the capacitive effect of distribution line are also considered. The proposed scheme was evaluated and tested on a modified IEEE 34-bus distribution system using PSCAD/EMTDC software.

Robust Control of Fault-Tolerant Permanent-Magnet Synchronous Motor for Aerospace Application With Guaranteed Fault Switch Process

Abstract: This paper proposes a novel ten-phase fault-tolerant permanent-magnet synchronous motor (FTPMSM) with two stators and two rotors on the same shaft. Furthermore, a concentrated, single-layer, and alternate-teeth-wound winding is adopted to enhance the fault isolation capacity of the motor. In addition, we propose a new approach to the speed control of the developed motor, which takes the electromagnetic torque ripple in the fault switch process into account. The control can guarantee the uniform boundedness and uniform ultimate boundedness of the system regardless of the load disturbance and the parameter variation, particularly for the fault switch process after a fault occurrence before the fault-tolerant control can take effect. Moreover, an optimal torque control is adopted to further improve the fault-tolerant performance, which enables a ripple-free torque operation under open-circuit and short-circuit fault conditions. Simulation and experimental results show that the FTPMSM system with the proposed control strategy has excellent fault-tolerant performance and good robustness. This paper provides an innovative approach by employing a robust control for a speed loop to guarantee the fault-tolerant performance of the proposed motor system under normal and fault conditions, even in the fault switch process.

A Novel Method for Single and Simultaneous Fault Location in Distribution Networks

Abstract: This paper introduces a novel method for single and simultaneous fault location in distribution networks by means of a sparse representation (SR) vector, Fuzzy-clustering, and machine-learning. The method requires few smart meters along the primary feeders to measure the pre- and during-fault voltages. The voltage sag values for the measured buses produce a vector whose dimension is less than the number of buses in the system. By concatenating the corresponding rows of the bus impedance matrix, an underdetermined set of equation is formed and is used to recover the fault current vector. Since the current vector ideally contains few nonzero values corresponding to fault currents at the faulted points, it is a sparse vector which can be determined by $\ell^{{{1}}}$ -norm minimization. Because the number of nonzero values in the estimated current vector often exceeds the number of fault points, we analyze the nonzero values by Fuzzy-c mean to estimate four possible faults. Furthermore, the nonzero values are processed by a new machine learning method based on the k-nearest neighborhood technique to estimate a single fault location. The performance of our algorithms is validated by their implementation on a real distribution network with noisy and noise-free measurement.

Real-Time Traveling-Wave-Based Fault Location Using Two-Terminal Unsynchronized Data

Abstract: In this paper, a new two-terminal traveling-wave-based fault-location algorithm is proposed. Its main advantage over similar two-terminal algorithms lies in the fact it does not require the data from both line terminals to be synchronized. In order to do so, the algorithm is applied in real time, and a communication system is used, whose data-transmission latency is taken into account in the proposed formulation. The fault locator routines were implemented using the real-time digital simulator (RTDS), such that a wide variety of fault scenarios in a 230-kV transmission line 200 km long was evaluated in real time, considering communication systems with different latency variability levels. The obtained results indicate the proposed algorithm is able to locate faults using either synchronized or unsynchronized two-terminal data, whereas classical methods work properly for synchronized measurements only.

Testing Open Defects in Memristor-Based Memories

Abstract: Memristor-based memory technology, also referred to as resistive RAM (RRAM), is one of the emerging memory technologies potentially to replace conventional semiconductor memories such as SRAM, DRAM, and flash. Existing research on such novel circuits focuses mainly on the integration between CMOS and non-CMOS, fabrication techniques, and reliability improvement. However, research on (manufacturing) test for yield and quality improvement is still in its infancy stage. This paper presents fault analysis and modeling for open defects based on electrical simulation, introduces fault models, and proposes test approaches for RRAMs. The fault analysis reveals that unique faults occur in addition to some conventional memory faults, and the detection of such unique faults cannot be guaranteed with just the application of traditional march tests. The paper also presents a new Design-for-Testability (DfT) concept to facilitate the detection of the unique faults. Two DfT schemes are developed by exploiting the access time duration and supply voltage level of the RRAM cells, and their simulation results show that the fault coverage can be increased with minor circuit modification. As the fault behavior may vary due to process variations, the DfT schemes are extended to be programmable to track the changes and further improve the fault/defect coverage.

Enhancing the performance of transmission line directional relaying, fault classification and fault location schemes using fuzzy inference system

Abstract: This study aims to improve the performance of transmission line directional relaying, fault classification and fault location schemes using fuzzy system. Three separate fuzzy inference system are designed for complete protection scheme for transmission line. The proposed technique is able to accurately detect the fault (both forward and reverse), locate and also identify the faulty phase(s) involved in all ten types of shunt faults that may occur in a transmission line under different fault inception angle, fault resistances and fault location. The proposed method needs current and voltage measurements available at the relay location and can perform the fault detection and classification in about a half-cycle time. The proposed fuzzy logic based relay has less computation complexity and is better than other AI based methods such as artificial neural network, support vector machine, and decision tree (DT) etc. which require training. The percentage error in fault location is within 1 km for most of the cases. Fault location scheme has been validated using χ2 test with 5% level of significance. Proposed scheme is a setting free method and is suitable for wide range of parameters, fault detection time is less than half cycle and relay does not show any reaching mal-operation so it is reliable, accurate and secure.

Single-Switch DC–DC Converter With Fault-Tolerant Capability Under Open- and Short-Circuit Switch Failures

Abstract: This paper proposes fault-tolerant (FT) operation of a single-switch dc-dc converter under a switch failure. In order to improve the reliability in critical applications, FT operation is mandatory to guarantee service continuity. The FT operation of a power system can be performed in three steps: fault diagnosis (detection and identification) and remedial actions. In the case of a switch failure, suitable fault detection is essential to avoid its propagation to the whole system. This study is based on a fast and efficient open- and short-circuit switch fault diagnosis. Both types of switch failure can be detected, identified, and handled in real time by implementing fault diagnosis and reconfiguration strategies on a field-programmable gate array target. No additional sensor is required to perform the fault detection. A redundant switch and a bidirectional switch are needed for converter reconfiguration in postfault operation. The results of hardware-in-the-loop and experimental tests, which all confirm the good performances of the proposed approach, are presented and discussed.

Comprehensive Modeling and Experimental Testing of Fault Detection and Management of a Nonredundant Fault-Tolerant VSI

Abstract: This paper presents an investigation and a comprehensive analysis on fault operations in a conventional three-phase voltage source inverter. After an introductory section dealing with power converter reliability and fault analysis issues in power electronics, a generalized switching function accounting for both healthy and faulty conditions and an easy and feasible method to embed fault diagnosis and reconfiguration within the control algorithm are introduced. The proposed system has simple and compact implementation. Experimental results operating both at open- and closed-loop current control, obtained using a test bench realized using a dSPACE system and the fault-tolerant inverter prototype demonstrate that the proposed solution is effective and feasible and makes all faults easily managed by the controller itself.

Synchrophasor-Based Wide-Area Backup Protection Scheme with Data Requirement Analysis

Abstract: This paper presents a fast and robust wide-area backup protection scheme to detect the faulty condition and to identify the faulted line in a large power network The proposed methodology uses positive-sequence synchrophasor data captured by either digital relays with synchronization capability or phasor measurement units dispersed over the network The basic idea behind the new protection scheme is the comparison of bus voltage values calculated through dissimilar paths Upon occurrence of a fault, the faulty condition is first detected and the bus(es) connected to the faulted line is(are) determined Among transmission lines connected to the suspected bus(es), the faulted one is thereafter identified In addition to two-terminal transmission lines, multiterminal lines are also incorporated The performance of the proposed method is validated on the IEEE 57-bus test system in different fault conditions (fault type, fault location, and fault resistance) Discrimination of faulty and normal conditions is simulated by examining various stressed conditions, for example, load encroachment, generator outage, and power swing The data requirement of the proposed technique is analyzed as well To do so, a mathematical model for the optimal placement of measurement devices is developed and applied to different IEEE standard test systems

Detection, Classification, and Estimation of Fault Location on an Overhead Transmission Line Using S-transform and Neural Network

Abstract: This article demonstrates a technique for diagnosis of fault type and faulty phase on overhead transmission lines. A method for computation of fault location is also incorporated in this work. The proposed method is based on the multi-resolution S-transform, which is used for generating complex S-matrices of the current signals measured at the sending and receiving ends of the line. The peak magnitude of the absolute value of every S-matrix is noted. The phase angle corresponding to every peak component is obtained from the argument of the relevant S-matrix. These features are used as input vectors of a probabilistic neural network for fault detection and classification. Detection of faulty phase(s) is followed by estimation of fault location. The voltage signal of the affected phase is processed to generate the S-matrix. The frequency components of the S-matrices for different fault locations are used as input vectors for training a back-propagation neural network. The results are obtained with s...

Ground Fault Detection and Location for Ungrounded DC Traction Power Systems

Abstract: A fault protection and location method for ungrounded dc traction power systems is presented in this paper. Many dc traction power systems have an ungrounded power circuit to increase the leakage path resistance. Although ungrounded systems can continue operating with a single ground contact, unlike solid- or low-resistance grounded systems, because of the very low fault current, a second ground fault in another pole will result in a line-to-line fault that could cause significant system damage. However, it is difficult to detect the first ground contact due to the low ground current and even harder to locate because it can be seen by many detectors in the network. The proposed scheme in this paper uses a probe unit to detect and locate the first single ground fault in ungrounded traction power systems. The probe unit applies probe voltage to detect the fault and, once the fault is detected, analyzes the response to dc or swept-frequency ac probe voltage to locate the fault. The proposed concepts have been verified with computer simulations and hardware experiments and demonstrated a successful performance.

Robust sliding-mode observer-based sensor fault estimation, actuator fault detection and isolation for uncertain nonlinear systems

Abstract: This paper deals with the issues of sensor fault estimation, actuator fault detection and isolation for a class of uncertain nonlinear systems. By taking the sensor fault vector as a part of an extended state vector, the original system with sensor faults, actuator faults and unknown inputs is transformed into an augmented singular system which is just with actuator faults and unknown inputs. For the constructed singular system, a robust sliding-mode observer is developed to simultaneously estimate the states and sensor faults of original system, and the observer gain matrices are computed in terms of linear matrix inequalities by solving an optimization problem. Then an actuator fault detector is designed to detect actuator faults when ones occur, and multiple observers used as actuator fault isolators are proposed to identify which actuator is with fault. Finally, a simulation example is given to illustrate the effectiveness of the proposed methods.

Fault Detection Analysis of Boolean Control Networks

Abstract: In this technical note, we address the fault detection problem for Boolean control networks (BCNs). We first investigate completeness and $T$ -completeness of the set of input/output trajectories. Next, we introduce the concept of meaningful fault, and prove necessary and sufficient conditions under which meaningful faults can be detected from the input/output trajectories of the BCN. Two fault detection algorithms are provided.

A Straightforward Method for Wide-Area Fault Location on Transmission Networks

Abstract: Local practices in fault location require measurements from one or more terminals of the faulted line to be available. On the other hand, the nonlinearity of circuit equations associated with wide-area fault location makes their solving process iterative and computationally demanding. This paper proposes a non-iterative method for wide-area fault location by taking advantage of the substitution theorem. Accordingly, a system of equations is constructed which can be easily solved using the linear least-squares method. The distributed-parameter line model is considered to provide a highly accurate estimation. Besides, due to inherent errors of current transformers, the current data is not taken into account to preserve the accuracy. In order to avoid uncertainties in relation with construction of zero-sequence network, just positive- and negative-sequence networks are exploited. Nonetheless, the method still is capable of pinpointing all types of short-circuit faults by using a restricted number of synchronized pre- and post-fault voltage phasors. Numerous simulation studies conducted on the WSCC 9-bus and New England 39-bus test systems verify the effectiveness and applicability of the proposed fault location method, even with limited coverage of synchronized measurements.

Unsynchronised fault-location technique for three-terminal lines

Abstract: This study describes a new fault-location technique using negative-sequence voltage for three-terminal lines. The ratios between the negative-sequence voltage magnitudes measured at each terminal are utilised to first determine the faulted section and then to estimate the exact fault location within the section. Since the current data is not deployed, the influence of inherent errors of current transformers can be avoided. The proposed method can accurately locate the unbalanced faults, that is, single-phase-to-ground, double-phase-to-ground, and phase-to-phase faults, regardless of the fault resistance and pre-fault conditions and without any need to identify the fault type. The method requires only the negative-sequence reactance behind each terminal which can be estimated by the short-circuit analysis with an acceptable accuracy. Reliability and practicality of the proposed method make it an attractive option to include in numerical protective relays. Simulation experiments with different fault cases reveal the capability of the proposed method.

Cost-Effective Three-Phase PMSM Drive Tolerant to Open-Phase Fault

Abstract: This paper presents a low-cost fault-tolerant system for open-phase fault (OPF) in a power-converter-fed permanent-magnet synchronous machine. The proposed fault-tolerant system is based on field orientation control with additional fault tolerance functionality. A current predictive method for OPF detection is presented, together with an estimation of the threshold level for detection. The proposed method is based on the prediction of stator current for the next sampling interval. Furthermore, a new method for postfault operation of the machine is proposed. For optimal performance of the complete drive, a prefiring angle is introduced in order to avoid the temporary generation of negative torque. This improvement increases the average generated postfault electromagnetic torque, and consequently, it reduces the mechanical stress on various machine parts. The proposed fault detection and postfault operation solutions were simulated in MATLAB, and they were also tested on an experimental setup. The results show several advantages of the proposed fault-tolerant solution, like its short fault-detection time, substantial robustness against variation of machine parameters or load fluctuations, and negligible implementation costs, since no hardware modifications are needed. The fault detection algorithm does not require high computing power, and it operates well even during transients.

Yield and Reliability Improvement Techniques for Emerging Nonvolatile STT-MRAM

Abstract: The emerging spin transfer torque magnetic random access memory (STT-MRAM) promises many attractive features, such as nonvolatile, high speed and low power etc, which enable it to be a promising candidate for the next-generation logic and memory circuits. However with the continuous scaling technology process, the chip yield and reliability of STT-MRAM face severe challenges due to the increasing permanent and transient faults. Due to the intrinsic fault features and the targeted application requirements of STT-MRAM, traditional fault tolerant design solutions, such as error correction code (ECC), redundancy repair (RR), and fault masking (FM) techniques, cannot be employed straightforwardly for STT-MRAM. In this paper, we propose a synergistic technique framework, named sECC, that integrates both the ECC and FM techniques to address simultaneously the permanent and transient faults. With such approach, permanent faults are masked while transient faults are corrected with the same codeword. Moreover taking into consideration the fact that most permanent faults are sparse [about 60%–70% single isolated faults (SIFs)], we propose further integrating the RR and sECC (named iRRsECC) to optimize the system performance. In this scenario, all the SIFs are masked and the transient faults are corrected with the proposed sECC, while other permanent faulty types (e.g., faulty rows or columns) are repaired with redundant rows or columns. A simulation tool is developed to evaluate the proposed techniques and the evaluation results show their good performance in terms of repair rate and hardware overhead.

Harmonic Order Tracking Analysis: A Novel Method for Fault Diagnosis in Induction Machines

Abstract: The diagnosis of induction machines using Fourier transform relies on tracking the frequency signature of each type of fault in the current's spectrum, but this signature depends on the machine's slip and the supply frequency, so it must be recomputed for each working condition by trained personnel or by diagnostic software. Besides, sampling the current at high rates during long times is needed to achieve a good spectral resolution, which requires large memory space to store and process the current spectra. In this paper, a novel approach is proposed to solve both problems. It is based on the fact that each type of fault generates a series of harmonics in the current's spectrum, whose frequencies are multiples of a characteristic main fault frequency. The tracking analysis of the fault components using the harmonic order (defined as the frequency in per unit of the main fault frequency) as independent variable instead of the frequency generates a unique fault signature, which is the same for any working condition. Besides, this signature can be concentrated in just a very small set of values, the amplitudes of the components with integer harmonic order. This new approach is introduced theoretically and validated experimentally.

A Fault-Location Algorithm for Series-Compensated Double-Circuit Transmission Lines Using the Distributed Parameter Line Model

Abstract: A new fault-location algorithm for series-compensated double-circuit transmission lines utilizing two-terminal unsynchronized voltage and current measurements is presented in this paper. The mutual coupling between the parallel lines in the zero-sequence network is fully considered. The distributed parameter line model is adopted to fully take into account the shunt capacitance of the line. By formulating voltages and currents at the fault point in terms of the unknown fault location, boundary conditions under different fault types are used to derive the fault location. Two subroutines assuming the fault occurs on the left or right side of the series compensator are developed and the principle to identify the correct fault-location estimate is described. Matlab SimPowerSystems is employed to generate cases under diverse fault conditions for validating the proposed fault-ocation algorithm. Evaluation studies have shown that the proposed algorithm has achieved quite accurate results.