The ultimate goal for power electronics is to convert one form of raw electrical energy into a usable power source with the lowest amount of loss. A considerable portion of these losses are due to the use of switching devices themselves. Device losses can be apportioned to conduction loss and switching loss. It is commonly known and practiced that conduction loss can be reduced by driving MOSFETs and IGBTs harder with gate voltages closer to the maximum rating. This lowers the voltage across the device in the path of the amplified current and ultimately reduces power dissipated by the device. However, switching losses of these devices are not as easily characterized or intuitive for power electronics designers. This is mainly due to the fact that the parasitic reactive elements are nonlinear and not as readily documented as I-V characteristics of a given power device. For example, non-linear parasitic capacitances in the device are given for a fixed frequency across a voltage sweep. Parasitic inductance is typically not even mentioned in the datasheet. The switching losses of these devices depend on these mysterious reactances. A functional way to obtain estimates of switching loss is to test the device under the conditions the device will be used. However, this task must be approached carefully in order to accurately measure the voltage and current of the device. Measurement devices also have parasitic impedances of their own that can add or subtract to switching energy during turn on or turn off and create misleading results. Preliminary testing was performed on multiple devices. After preliminary testing and deliberation, a device-measurement printed circuit board was made to easily replace switching devices of the same package. This thesis presents switching loss measurements of medium-power capable devices in the tens of kW range. It also aims to attribute characteristics of switching voltage and current waveforms to the internal structure of the devices. The device tester designed is versatile since the output buffer of the gate drive is comprised of D-PAK totem pole BJTs. This is able to drive both current and voltage driven devices, i.e. SiC J-FETs (current-driven) and other voltage-driven devices (i.e. MOSFETs and IGBTs). It also allows for TO-220 and TO-247 packaged power diodes. / Master of Science

В работе решается проблема автоматизации тестирования устройств Интернета вещей. Для ее решения разрабатывается платформа тестирования, которая позволяет автоматизировать этот процесс. Чтобы упростить работу пользователя с платформой, реализован интерфейс связи. Он обеспечивает взаимодействие между различными компонентами платформы автоматизированного тестирования устройств. Предлагаемый вариант решения позволяет клиентскому приложению установить связь с серверной частью и сделать процесс выявления неполадок более эффективным. Разработанное веб-приложение позволяет в реальном времени получать актуальную информацию о ходе тестирования и сохранять результаты после ее завершения. Работы по тестированию проводились на электросчетчике Милур 307 с модулем Карат-941LW. Автоматизация позволила значительно сократить время испытаний по сравнению с ручным тестированием. / The work solves the problem of automating testing of IoT devices. To solve it, a testing platform is being developed that allows you to automate this process. To simplify the user's work with the platform, a communication interface has been implemented. It provides interoperability between the various components of the automated device testing platform. The proposed solution allows the client application to communicate with the back end and make the troubleshooting process more efficient. The developed web application allows you to receive up-to-date information about the testing progress in real time and save the results after its completion. Testing works were carried out on the Milur 307 electric meter with the Karat-941LW module. Automation has significantly reduced test time compared to manual testing.

В работе поднимается проблема отсутствия необходимых методов и технологий тестирования устройств Интернета вещей в автоматическом режиме. В качестве решения проблемы предложена методология тестирования встроенного программного обеспечения «умных» устройств. Методология была реализована в сервисе «ядро тестирования». Апробация работы сервиса проводились на примере проведения испытаний счетчика электрической энергии Милур 307 с интерфейсным модулем Карат-941LW. Автоматизация позволила значительно сократить время испытаний по сравнению с ручным тестированием. / The thesis raises the problem of the lack of necessary methods and technologies for testing IoT devices in automatic mode. As a solution to the problem, a methodology for testing the embedded software of “smart” devices is proposed. The methodology was implemented in the testing core service. The approbation of the service was carried out on the example of testing the Milur 307 electric energy meter with the Karat-941LW interface module. Automation has significantly reduced test time compared to manual testing.

Работа посвящена решению проблемы ручного тестирования устройств Интернета вещей. Предлагается использовать разработанную платформу автоматизированного тестирования встроенного программного обеспечения. Для удобного взаимодействия с платформой разработано клиентское веб-приложение, которое включает в себя конструктор тестов и мониторинг состояния платформы. Веб-приложение конструктора тестов реализовано для создания тестов для IoT-устройств. Наличие мониторинга позволяет определять работоспособность платформы и отслеживать выполнение процесса тестирования устройств. Работы по тестированию проводились на приборе Милур 307 с модулем Карат-941LW. Автоматизация позволила значительно сократить время испытаний по сравнению с ручным тестированием. / The work is devoted to solving the problem of manual testing of Internet of Things devices. It is proposed to use the developed platform for automated testing of embedded software. For convenient interaction with the platform, a client web application has been developed that includes a test designer and monitoring of the platform state. Test builder is developed for creating tests for IoT devices. The presence of monitoring allows to determine the health of the platform and track the progress of the device testing process. Testing works were carried out on the Milur 307 electric meter with the Karat-941LW module. Automation has significantly reduced test time compared to manual testing.

<p>In this thesis, inferential methods for one-shot device testing data from accelerated life-test are developed. Due to constraints on time and budget, accelerated life-tests are commonly used to induce more failures within a reasonable amount of test-time for obtaining more lifetime information that will be especially useful in reliability analysis. One-shot devices, which can be used only once as they get destroyed immediately after testing, yield observations only on their condition and not on their real lifetimes. So, only binary response data are observed from an one-shot device testing experiment. Since no failure times of units are observed, we use the EM algorithm for determining the maximum likelihood estimates of the model parameters. Also, inference for the reliability at a mission time and the mean lifetime at normal operating conditions are also developed.</p> <p>The thesis proceeds as follows. Chapter 2 considers the exponential distribution with single-stress relationship and develops inferential methods for the model parameters, the reliability and the mean lifetime. The results obtained by the EM algorithm are compared with those obtained from the Bayesian approach. A one-shot device testing data is analyzed by the proposed method and presented as an illustrative example. Next, in Chapter 3, the exponential distribution with multiple-stress relationship is considered and corresponding inferential results are developed. Jackknife technique is described for the bias reduction in the developed estimates. Interval estimation for the reliability and the mean lifetime are also discussed based on observed information matrix, jackknife technique, parametric bootstrap method, and transformation technique. Again, we present an example to illustrate all the inferential methods developed in this chapter. Chapter 4 considers the point and interval estimation for the one-shot device testing data under the Weibull distribution with multiple-stress relationship and illustrates the application of the proposed methods in a study involving the development of tumors in mice with respect to risk factors such as sex, strain of offspring, and dose effects of benzidine dihydrochloride. A Monte Carlo simulation study is also carried out to evaluate the performance of the EM estimates for different levels of reliability and different sample sizes. Chapter 5 describes a general algorithm for the determination of the optimal design of an accelerated life-test plan for one-shot device testing experiment. It is based on the asymptotic variance of the estimated reliability at a specific mission time. A numerical example is presented to illustrate the application of the algorithm. Finally, Chapter 6 presents some concluding remarks and some additional research problems that would be of interest for further study.</p> / Doctor of Philosophy (PhD)

This diploma thesis deals with the design and implementation of a computer-controlled device for testing gas boiler control units, especially in the development phase. The reason for creating a test facility is the inadequacy of older test systems and the automation of existing testing. The test device in development consists of individual different cards. Each of the cards inserted into the motherboard performs its function in the system. Each of the cards has a special functionality which simulates the real conditions of the developed product. The basis of most cards is a microcontroller with a Cortex-M core, which communicates with the connected computer using the MODBUS protocol on the RS-485 communication interface. All cards on the bus are connected in parallel and behaves as a SLAVE, while the computer behaves as a MASTER and requests data or sends commands to the cards. The cards represent status switches (switching sensors), resistance and analog temperature sensors, PWM inputs and outputs (for simulation of feedback pumps or flow meters with pulse output). The cards also include a flame simulator, which reliably simulates the electrical properties of the flame and at the same time acts as a fan simulator. The input of the control unit is taken care of by the input card, which is intended for digital detection of the voltage presence in the range of 5 to 230 V DC and AC. Simultaneously, a card for connecting the power supply at zero voltage and disconnecting at zero current is created to supply the tested device with alternating voltage. A schematic diagram was designed or simulated for each card, then the function was verified and on this basis the whole card was created, including the microcontroller firmware. The most suitable solution and function of each card is carefully described and evaluated. All the requirements of the assignment within the work were met and the whole test equipment was manufactured and verified in four versions. In the future, the device is ready for the implementation of an automatic flame simulator and other improvements of individual module cards.

In this thesis, we develop some inferential results for one-shot device testing data analysis. These extend and generalize existing methods in the literature. First, a competing-risk model is introduced for one-shot testing data under accelerated life-tests. One-shot devices are products which will be destroyed immediately after use. Therefore, we can observe only a binary status as data, success or failure, of such products instead of its lifetime. Many one-shot devices contain multiple components and failure of any one of them will lead to the failure of the device. Failed devices are inspected to identify the specific cause of failure. Since the exact lifetime is not observed, EM algorithm becomes a natural tool to obtain the maximum likelihood estimates of the model parameters. Here, we develop the EM algorithm for competing exponential and Weibull cases. Second, a semi-parametric approach is developed for simple one-shot device testing data. Semi-parametric estimation is a model that consists of parametric and non-parametric components. For this purpose, we only assume the hazards at different stress levels are proportional to each other, but no distributional assumption is made on the lifetimes. This provides a greater flexibility in model fitting and enables us to examine the relationship between the reliability of devices and the stress factors. Third, Bayesian inference is developed for one-shot device testing data under exponential distribution and Weibull distribution with non-constant shape parameters for competing risks. Bayesian framework provides statistical inference from another perspective. It assumes the model parameters to be random and then improves the inference by incorporating expert's experience as prior information. This method is shown to be very useful if we have limited failure observation wherein the maximum likelihood estimator may not exist. The thesis proceeds as follows. In Chapter 2, we assume the one-shot devices to have two components with lifetimes having exponential distributions with multiple stress factors. We then develop an EM algorithm for developing likelihood inference for the model parameters as well as some useful reliability characteristics. In Chapter 3, we generalize to the situation when lifetimes follow a Weibull distribution with non-constant shape parameters. In Chapter 4, we propose a semi-parametric model for simple one-shot device test data based on proportional hazards model and develop associated inferential results. In Chapter 5, we consider the competing risk model with exponential lifetimes and develop inference by adopting the Bayesian approach. In Chapter 6, we generalize these results on Bayesian inference to the situation when the lifetimes have a Weibull distribution. Finally, we provide some concluding remarks and indicate some future research directions in Chapter 7. / Thesis / Doctor of Philosophy (PhD)

A device that is accompanied by an irreversible chemical reaction or physical destruction and could no longer function properly after performing its intended function is referred to as a one-shot device. One-shot device test data differ from typical data obtained by measuring lifetimes in standard life-tests. Due to the very nature of one-shot devices, actual lifetimes of one-shot devices under test cannot be observed, and they are either left- or right-censored. In addition, a one-shot device often has multiple components that could cause the failure of the device. The components are coupled together in the manufacturing process or assembly, resulting in the failure modes possessing latent heterogeneity and dependence. Frailty models enable us to describe the influence of common, but unobservable covariates, on the hazard function as a random effect in a model and also provide an easily understandable interpretation. In this thesis, we develop some inferential results for one-shot device testing data with gamma frailty model. We first develop an efficient expectation-maximization (EM) algorithm for determining the maximum likelihood estimates of model parameters of a gamma frailty model with exponential lifetime distributions for components based on one-shot device test data with multiple failure modes, wherein the data are obtained from a constant-stress accelerated life-test. The maximum likelihood estimate of the mean lifetime of $k$-out-of-$M$ structured one-shot devices under normal operating conditions is also presented. In addition, the asymptotic variance–covariance matrix of the maximum likelihood estimates is derived, which is then used to construct asymptotic confidence intervals for the model parameters. The performance of the proposed inferential methods is finally evaluated through Monte Carlo simulations and then illustrated with a numerical example. A gamma frailty model with Weibull baseline hazards is considered next for fitting one-shot device testing data. The Weibull baseline hazards enable us to analyze time-varying failure rates more accurately, allowing for a deeper understanding of the dynamic nature of system's reliability. We develop an EM algorithm for estimating the model parameters utilizing the complete likelihood function. A detailed simulation study evaluates the performance of the Weibull baseline hazard model with that of the exponential baseline hazard model. The introduction of shape parameters in the component's lifetime distribution within the Weibull baseline hazard model offers enhanced flexibility in model fitting. Finally, Bayesian inference is then developed for the gamma frailty model with exponential baseline hazard for one-shot device testing data. We introduce the Bayesian estimation procedure using Markov chain Monte Carlo (MCMC) technique for estimating the model parameters as well as for developing credible intervals for those parameters. The performance of the proposed method is evaluated in a simulation study. Model comparison between independence model and the frailty model is made using Bayesian model selection criterion. / Thesis / Candidate in Philosophy