48 research outputs found

    Fault Diagnosis and Condition Monitoring of Power Electronic Components Using Spread Spectrum Time Domain Reflectometry (SSTDR) and the Concept of Dynamic Safe Operating Area (SOA)

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    Title from PDF of title page viewed April 1, 2021Dissertation advisors: Faisal Khan and Yong ZengVitaIncludes bibliographical references ( page 117-132)Thesis (Ph.D.)--School of Computing and Engineering and Department of Mathematics and Statistics. University of Missouri--Kansas City, 2021Fault diagnosis and condition monitoring (CM) of power electronic components with a goal of improving system reliability and availability have been one of the major focus areas in the power electronics field in the last decades. Power semiconductor devices such as metal oxide semiconductor field-effect transistor (MOSFET) and insulated-gate bipolar transistor (IGBT) are considered to be the most fragile element of the power electronic systems and their reliability degrades with time due to mechanical and thermo-electrical stresses, which ultimately leads to a complete failure of the overall power conversion systems. Therefore, it is important to know the present state of health (SOH) of the power devices and the remaining useful life (RUL) of a power converter in order to perform preventive scheduled maintenance, which will eventually lead to increased system availability and reduced cost. In conventional practice, device aging and lifetime prediction techniques rely on the estimation of the meantime to failure (MTTF), a value that represents the expected lifespan of a device. MTTF predicts expected lifespan, but cannot adequately predict failures attributed to unusual circumstances or continuous overstress and premature degradation. This inability is due in large part to the fact that it considers the device safe operating area (SOA) or voltage and current ride-through capability to be independent of SOH. However, we experimentally proved that SOA of any semiconductor device goes down with the increased level of aging, and therefore, the probability of occurrence of over-voltage/current situation increases. As a result, the MTTF of the device as well as the overall converter reliability reduces with aging. That said, device degradation can be estimated by accomplishing an accurate online degradation monitoring tool that will determine the dynamic SOA. The correlation between aging and dynamic SOA gives us the useful remaining life of the device or the availability of a circuit. For this monitoring tool, spread spectrum time domain reflectometry (SSTDR) has been proposed and was successfully implemented in live power converters. In SSTDR, a high-frequency sine-modulated pseudo-noise sequence (SMPNS) is sent through the system, and reflections from age-related impedance discontinuities return to the test end where they are analyzed. In the past, SSTDR has been successfully used for device degradation detection in power converters while running at static conditions. However, the rapid variation in impedance throughout the entire live converter circuit caused by the fast-switching operation makes CM more challenging while using SSTDR. The algorithms and techniques developed in this project have overcome this challenge and demonstrated that the SSTDR test data are consistent with the aging of the power devices and do not affect the switching performance of the modulation process even the test signal is applied across the gate-source interface of the power MOSFET. This implies that the SSTDR technique can be integrated with the gate driver module, thereby creating a new platform for an intelligent gate-driver architecture (IGDA) that enables real-time health monitoring of power devices while performing features offered by a commercially available driver. Another application of SSTDR in power electronic systems is the ground fault prediction and detection technique for PV arrays. Protecting PV arrays from ground faults that lead to fire hazards and power loss is imperative to maintaining safe and effective solar power operations. Unlike many standard detection methods, SSTDR does not depend on fault current, therefore, can be implemented for testing ground faults at night or low illumination. However, wide variation in impedance throughout different materials and interconnections makes fault location more challenging than fault detection. This barrier was surmounted by the SSTDR-based fault detection algorithm developed in this project. The proposed algorithm was accounted for any variation in the number of strings, fault resistance, and the number of faults. In addition to its general utility for fault detection, the proposed algorithm can identify the location of multiple faults using only a single measurement point, thereby working as a preventative measure to protect the entire system at a reduced cost. Within the scope of the research work on SSTDR-based fault diagnosis and CM of power electronic components, a cell-level SOH measurement tool has been proposed that utilizes SSTDR to detect the location and aging of individual degraded cells in a large series-parallel connected Li-ion battery pack. This information of cell level SOH along with the respective cell location is critical to calculating the SOH of a battery pack and its remaining useful lifetime since the initial SOH of Li-ion cells varies under different manufacturing processes and operating conditions, causing them to perform inconsistently and thereby affect the performance of the entire battery pack in real-life applications. Unfortunately, today’s BMS considers the SOH of the entire battery pack/cell string as a single SOH and therefore, cannot monitor the SOH at the cell level. A healthy battery string has a specific impedance between the two terminals, and any aged cell in that string will change the impedance value. Since SSTDR can characterize the impedance change in its propagation path along with its location, it can successfully locate the degraded cell in a large battery pack and thereby, can prevent premature failure and catastrophic danger by performing scheduled maintenance.Introduction -- Background study and literature review -- Fundamentals of Spread Spectrum Time Domain Reflectometry (SSTDR): A new method for testing electronics live -- Accelerated aging test bench: design and implementation -- Condition monitoring of power switching in live power switching devices in live power electronic converters using SSTDR -- An irradiance-independent, robust ground-fault detection scheme for PV arrays based on SSTDR -- Detection of degraded/aged cell in a LI-Ion battery pack using SSTDR -- Dynamiv safe operating area (SOA) of power semiconductor devices -- Conclusion and future researc

    Master of Science

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    thesisThe focus of this thesis is the impact and use of crosstalk and coupling when testing for electrical wiring faults using reflectometry. This thesis describes a method for detecting and locating faults on cable shields using an adapted reflectometry system. A signal transmitted on the inner conductor is coupled to the outside through the fault, a small aperture in the cable shielding. This very small signal is then detected and correlated with the original signal transmitted on the inner conductor. The signals that leak out of the aperture, the damaged shield, and propagate down the outside of the cable are quantified as a function of the aperture size and frequency. A ferrite loaded toroidal sensor design is also proposed for receiving this external signal in order to both detect and localize the shield damage. Both simulations and measurements validate the effectiveness of this method. Unshielded discrete wires are another common type of transmission line. While unshielded wires are primarily used for DC power, they are still subject to degradation over time and require maintenance. Unlike shielded cables, there is a significant amount of coupling that occurs between adjacent wires during a reflectometry test. This coupling is quantified and evaluated for two applications. The first is simultaneous testing of multiple adjacent wires in a bundle. In this case, minimizing the coupling is desirable in order to reduce noise in the reflectometry signature. The second is the exploration of the potential for a single reflectometry test to locate faults on adjacent wires without directly testing them. When a single test is performed in a multiwire bundle, the reflectometry signature will be a superposition of reflections from all nearby conductors. This thesis addresses the testing of a multiconductor wiring structure with a common signal reference as well as a similar structure with an isolated signal reference. In order to accurately detect faults on multiconductor wiring structures, both testing methods must be considered. A fault between a conductor and its reference conductor is easily detectable. A cross fault between two nonreference conductors is not. For cross fault consideration, the only method for detection is using a common signal reference and analyzing the data on adjacent lines

    PV ground-fault detection using spread spectrum time domain reflectometry (SSTDR)

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    pre-printA PV ground-fault detection technique using spread spectrum time domain reflectometry (SSTDR) method has been introduced in this paper. SSTDR is a reflectometry method that has been commercially used for detecting aircraft wire faults. Unlike other fault detection schemes for a PV system, ground fault detection using SSTDR does not depend on the amplitude of fault-current and highly immune to noise signals. Therefore, SSTDR can be used in the absence of the solar irradiation as well. The proposed PV ground fault detection technique has been tested in a real-world PV system and it has been observed that PV ground fault can be detected confidently by comparing autocorrelation values generated using SSTDR. The difference in the autocorrelation peaks before and after a ground-fault in the PV system are significantly higher than the threshold set for ground-fault detection

    Master of Science

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    dissertationPower converters are frequently exposed to electrical stresses such as over voltage, over current and switching impulses during their regular operations. These stresses may not result in immediate failure of a power converter. However, over longer periods they cause gradual degradation of critical components inside the converter, which ultimately leads to a complete failure of the converter. Failure of a power converter might disrupt the operation of the entire system, occasionally causing catastrophic outcomes. Estimating a converter's state of health and predicting the remaining life involves extensive research in semiconductor device physics and circuit theory, and is both important and challenging. There is always a dire need to determine the level of aging in power converters so that an approximate time to failure could be predicted. A reflectometry technique was applied to power converters to identify failure and aging associated to critical components inside a power converter. In addition, mechanisms for gradual shift in measurable electrical parameters of power converter components over long durations have been studied under the scope of the project. While there exist several other techniques for predicting reliability and aging of power converters, they are limited to characterizing isolated components only. Whereas using the proposed technique, estimating the component degradation in energized circuits is possible. Spread spectrum time domain reflectometry (SSTDR) has been commercially used for detecting aircraft wiring faults during the last decade, however, it was never applied to components in a power converter. During the preliminary stage of this project SSTDR was applied to a DC-DC converter circuit, and several key parameters such as MOSFETs ON resistance was extracted to characterize MOSFET aging. Later on, this technique was applied to different other components in an H-bridge AC-AC converter for failure rate estimation and reliability analysis. The MTTF (mean time to failure) was calculated based on the SSTDR generated data. The conducted research has initiated other SSTDR based prognostics and state of health measurement methods applicable to PV panels, electric machines and batteries

    Quantifying device degradation in live power converters using SSTDR assisted impedance Matrix

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    pre-printA noninterfering measurement technique designed around spread spectrum time domain reflectometry (SSTDR) has been proposed in this paper to identify the level of aging associated with power semiconductor switches inside a live converter circuit. Power MOSFETs are one of the most age-sensitive components in power converter circuits, and this paper demonstrates how SSTDR can be used to determine the characteristic degradation of the switching MOSFETs used in various power converters. An SSTDR technique was applied to determine the aging in power MOSFETs, while they remained energized in live circuits. In addition, SSTDR was applied to various test nodes of an H-bridge ac-ac converter, and multiple impedance matrices were created based on the measured reflections. An error minimization technique has been developed to locate and determine the origin and amount of aging in this circuit, and this technique provides key information about the level of aging associated to the components of interest. By conducting component level failure analysis, the overall reliability of an H-bridge ac-ac converter has been derived and incorporated in this paper

    Doctor of Philosophy

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    dissertationThree major catastrophic failures in photovoltaic (PV) arrays are ground-faults, line-to-line faults, and arc faults. Although the number of such failures is few, recent fire events on April 5, 2009, in Bakersfield, California, and April 16, 2011, in Mount Holly, North Carolina suggest the need for improvements in present fault detection and mitigation techniques, as well as amendments to existing codes and standards to avoid such accidents. A fault prediction and detection technique for PV arrays based on spread spectrum time domain reflectometry (SSTDR) has been proposed and was successfully implemented. Unlike other conventional techniques, SSTDR does not depend on the amplitude of the fault-current. Therefore, SSTDR can be used in the absence of solar irradiation as well. However, wide variation in impedance throughout different materials and interconnections makes fault locating more challenging than prediction/detection of faults. Another application of SSTDR in PV systems is the measurement of characteristic impedance of power components for condition monitoring purposes. Any characteristic variations in one component will simultaneously alter the operating conditions of other components in a closed-loop system, resulting in a shift in overall reliability profile. This interdependence makes the reliability of a converter a complex function of time and operating conditions. Details of this failure mode, mechanism, and effect analysis (FMMEA) have been developed. By knowing the present state of health and the remaining useful life (RUL) of a power converter, it is possible to reduce the maintenance cost for expensive high-power converters by facilitating a reliability centered maintenance (RCM) scheme. This research is a step forward toward power converter reliability analysis since the cumulative effect of multiple degraded components has been considered here for the first time in order to estimate reliability of a power converter

    Master of Science

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    thesisA network algorithm is developed to analyze a branched wire network to determine the branch and fault topology of the network, using an array of hand-held (EM) electro-magnetic field sensors in conjunction with a SSTDR (Spread-Spectrum Time Domain Reflectometry) wire tester. The algorithm provides an analysis of the convolved reflectometry data collected at multiple data points along a test wire by the field sensors. The faults are located using a reconstruction of forward and backward traveling waveforms created from a mathematical inversion of a collection of convolved reflectometry data. The methods and algorithms developed to model the topology of the test wires are described. The topology refers to the locations of the major reflection points within a branched network, and the lengths and connections of the segments of wire that exist between reflectors. Simulations are developed to determine the effectiveness of the algorithm without the limitations of the test hardware. Tests are performed in a controlled lab environment to assess the abilities of the developed algorithms

    Characterization of aging process in power converters using spread spectrum time domain reflectometry

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    pre-printThis paper aims to find a new technique to predict the state of health of power converters by characterizing the most vulnerable components in the converter without affecting the normal circuit operation. Spread spectrum time domain reflectometry (SSTDR) can detect most of the aged components inside the converter while the converter is operational. Semiconductor switches and electrolytic capacitors are the two most sensitive components in power converter circuits, and this paper demonstrated how SSTDR can be used to determine the degradation of these components. Multiple sets of test data have been generated while the SSTDR process is applied to the power MOSFETs, IGBTs connected in a chopper circuit and to the aluminum electrolytic capacitors connected in an RC circuit. Analysis is done on these obtained test data to show how the SSTDR generated data are consistent with the aging of power MOSFETs, IGBTs and electrolytic capacitors

    Low-power STDR CMOS sensor for locating faults in aging aircraft wiring

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    Journal ArticleA CMOS sensor used to locate intermittent faults on live aircraft wires is presented. A novel architecture was developed to implement the Sequence Time Domain Reflectometry method on a 0.5- m integrated circuit. The sensor locates short or open circuits on active wires with an accuracy of +/-1 ft when running at a clock speed of 100 MHz. A novel algorithm is proposed that utilizes the shape of the correlation peak to account for sub-bit delay, thus increasing the accuracy of fault location. The power consumed by the microchip is 39.9 mW

    Non-destructive examination (NDE) methods for dynamic subsea cables for Offshore Renewable Energy

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    This is the final version. Available on open access from IOP Publishing via the DOI in this recordData availability statement: The data that support the findings of this study are available upon reasonable request from the authors.Offshore renewable energy installations are moving into more challenging environments where fixed foundations are not economically viable, forcing the development of floating platforms. Subsea cables are critical for transfer of the power generated back to shore. The electrical capabilities of subsea cables are well understood; however, the structural capabilities are not, subsea power cable failures accounting for a significant proportion of insurance claims. Cables are challenging to repair, with specific vessels and good weather windows required, therefore making operations very costly. A good understanding of the internal structure of a subsea cable, and interaction between the layers, is integral to the development of robust and reliable, high voltage, dynamic, subsea cables. A requirement therefore exists for non-destructive examination (NDE) of live subsea cables to determine locations, and identify the causes, of faults and classify their type. An NDE framework such as this would assist in planning operations and reduce the risk and cost inherent to delivering offshore power. Improved understanding of subsea cable failure modes and mechanisms could also be achieved through us of NDE during onshore, dry, experimental testing. Three currently available NDE methods are considered, developed for use in other disciplines, for the purpose of structural monitoring of subsea power cables during onshore evaluation testing. The NDE methods were: (a) thermography, (b) eddy current testing (ECT), (c) spread spectrum time domain reflectometry (SSTDR). The methods are assessed with regards to the information that could be obtained from both a static and oscillating cable in pilot physical tests. The results of the testing were promising, with cable motions and interlayer movements being detected by all techniques to various degrees.Engineering and Physical Sciences Research Council (EPSRC
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