DESIGN AND RELIABILITY ASSESSMENT OF HIGH POWER LED AND LED-BASED SOLID STATE LIGHTING

Lumen depreciation and color quality change of high power LED-based solid state light (SSL) are caused by the combination of various degradation mechanisms. The analytical/experimental models on the system as well as component-level are proposed to analyze the complex reliability issues of the LED-based solid SSL. On the system-level front, a systematic approach to define optimum design domains of LED-based SSL for a given light output requirement is developed first by taking cost, energy consumption and reliability into consideration. Three required data sets (lumen/LED, luminaire efficacy, and L70 lifetime) to define design domains are expressed as contour maps in terms of two most critical operating parameters: the forward current and the junction temperature (If and Tj). Then, the available domain of design solutions is defined as a common area that satisfies all the requirements of a luminaire. Secondly, a physic of failure (PoF) based hierarchical model is proposed to estimate the lifetime of the LED-based SSL. The model is implemented successfully for an LED-based SSL cooled by a synthetic jet, where the lifetime of a prototypical luminaire is predicted from LED lifetime data using the degradation analyses of the synthetic jet and the power electronics. On the component-level front, a mathematical model and an experimental procedure are developed to analyze the degradation mechanisms of high power LEDs. In the approach, the change in the spectral power distribution (SPD) caused by the LED degradation is decomposed into the contributions of individual degradation mechanisms so that the effect of each degradation mechanism on the final LED degradation is quantified. It is accomplished by precise deconvolution of the SPD into the leaked blue light and the phosphor converted light. The model is implemented using the SPDs of a warm white LED with conformally-coated phosphor, obtained before and after 9,000 hours of operation. The analysis quantifies the effect of each degradation mechanism on the final values of lumen, CCT and CRI

Challenges and New Trends in Power Electronic Devices Reliability

The rapid increase in new power electronic devices and converters for electric transportation and smart grid technologies requires a deepanalysis of their component performances, considering all of the different environmental scenarios, overload conditions, and high stressoperations. Therefore, evaluation of the reliability and availability of these devices becomes fundamental both from technical and economicalpoints of view. The rapid evolution of technologies and the high reliability level offered by these components have shown that estimating reliability through the traditional approaches is difficult, as historical failure data and/or past observed scenarios demonstrate. With the aim topropose new approaches for the evaluation of reliability, in this book, eleven innovative contributions are collected, all focusedon the reliability assessment of power electronic devices and related components

CO2 savings from Micro-CHP : influence of operating regimes, demand variations and energy storage

A high temporal precision model was developed to assess the performance of thermal load following micro-CHP system design variants in detail for a number of design days. Carbon savings (relative to a base-case energy system) and prime mover lifetime drivers (thermal cycling and operating duration) were quantified. Novel performance metrics were defined, including Potential Thermal Supply Demand Ratio, and Effective Carbon Intensity of μCHP-Generated Electricity. Significant relative carbon savings were found for design variants with a PTSDR between 0.1-1.5, suggesting that it is a design selection parameter for thermal supply/demand matching. Alternative μCHP operating regimes, restricted seasonal operation, changing thermal demand, fuel and electricity grid carbon intensities, and energy storage (using batteries and hydrogen) were studied. It was found that annual relative carbon savings in excess of 23% were achievable for appropriately-sized design variants, with relatively high electrical efficiency, once a complex control strategy is applied. The control strategy also reduces thermal cycling for the μCHP design variant (versus the Thermal Load Following operating regime), hence increasing prime mover lifetime.Engineering and Physical Sciences Research Council (EPSRC