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A 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.Index Terms-Aging, converter, degradation, failure rate, matrix, mean time to failure (MTTF), reflectometry, reliability, spread spectrum time domain reflectometry (SSTDR).

Figure 1. The proposed technique to identify aging of various components using reflectometry without altering the main power flow of the converter.Abstract-This 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. I.978-1-4673-0803-8/12/$31.00 ©2012 IEEE

A new online measurement and analysis method has been presented in this paper to identify the state of health of power converter circuits. Using spread spectrum time domain reflectometry (SSTDR), impedance in the various current paths inside the converter as well as any fault can be identified without interrupting the circuit's normal operation. Multiple sets of test data have been generated while the SSTDR process is applied to each of the components i.e. the power MOSFETs, the dc bus capacitor and the load. These obtained test data are analyzed to show how these test results are consistent with the impedances in various current paths. An impedance matrix was formed for a non-aged converter and a corresponding matrix using SSTDR data was formed as well. The matrices could be formed for any power converter, and the impedance matrix for the non-aged converter could be considered as a "Reference matrix" for comparison purpose. By comparing these two matrices, the variation in path impedances due to aging could be determined. This research aims to identify the measurable quantities to characterize the aging process, their origins of these quantities and propose convenient methods to measure them.

A non-interfering measurement technique has been proposed in this paper to identify aging in various components in a power converter circuit. Several power MOSFETs and IGBTs were aged in a controlled environment, and spread spectrum time domain reflectometry (SSTDR) technique was applied to these components to determine the associated level of electrical degradation while they were connected in an energized circuit. Multiple impedance matrices have been created based on the measured reflection across multiple node pairs of the circuit, and these reflections are the true representations of the impedance across those node pairs. Therefore, these matrices provide key information about the level of electrical degradation associated to the core power components in the power circuit, and it is possible to predict the remaining life of the power converter by using this impedance matrices.