Doosan Heavy Industries & Construction (South Korea)

A novel control methodology for Multi-Active Bridge (MAB) converters, termed the Single PWM (SPWM) technique, aimed at reducing both conduction and switching losses, is proposed in this paper. The proposed control algorithm achieves soft switching across all load conditions while optimizing the converter's overall conduction loss by minimizing the RMS currents of the three ports for the MAB converters, particularly under light load conditions. By employing only two control variables— primary and secondary phase shifts (ɸd) and zero-voltage turn-on intervals (α or β)—the control complexity is significantly reduced compared to conventional MAB control algorithms, which rely on multiple variables and incur high computational overhead. The SPWM control method thus enables efficient and straightforward converter operation under both step-up and step-down conditions. Simulation and experimental results at a 10 kHz operating frequency and 70 kW power delivery demonstrate that the proposed method consistently achieves soft switching and minimizes the RMS currents of all three ports under various voltage and power conditions, leading to efficiency improvements of up to 0.6% compared to conventional SPWM techniques.

Shot peening is a surface treatment process that improves the fatigue life of a material and suppresses cracks by generating residual stress on the surface. The injected small shots create a compressive residual stress layer on the material’s surface. Maximum compressive residual stress occurs at a certain depth, and tensile residual stress gradually occurs as the depth increases. This process is primarily used for nickel-based superalloy steel materials in certain environments, such as the aerospace industry and nuclear power fields. To prevent such a severe accident due to the high-temperature and high-pressure environment, evaluating the residual stress of shot-peened materials is essential in evaluating the soundness of the material. Representative methods for evaluating residual stress include perforation strain gauge analysis, X-ray diffraction (XRD), and ultrasonic testing. Among them, ultrasonic testing is a representative, non-destructive evaluation method, and residual stress can be estimated using a Rayleigh wave. Therefore, in this study, the maximum compressive residual stress value of the peened Inconel 718 specimen was predicted using a prediction convolutional neural network (CNN) based on the relationship between Rayleigh wave dispersion and stress distribution on the specimen. By analyzing the residual stress distribution in the depth direction generated in the model from various studies in the literature, 173 residual stress distributions were generated using the Gaussian function and factorial design approach. The distribution generated using the relationship was converted into 173 Rayleigh wave dispersion data to be used as a database for the CNN model. The CNN model was learned through this database, and performance was verified using validation data. The adopted Rayleigh wave dispersion and convolutional neural network procedures demonstrate the ability to predict the maximum compressive residual stress in the peened specimen.

Abstract Doosan, the Heavy-duty gas turbine OEM manufacturer, have been successfully achieving the progress of developing hydrogen gas turbine combustor. Considering the low hydrogen production rate, the safety of hydrogen flame, and above all, the connection with green hydrogen production through eco-friendly energy generation, we started to develop a 5MW small sized gas turbine for 100% hydrogen, and we plan to gradually expand it to medium and large sizes combustors. This paper presents the results of testing four different types of good performance nozzles, selected from among the designed hydrogen concept nozzles with the idea for anti-flashback. The nozzles were verified and updated through commercial CFD analysis, and in this study, they were tested in an actual hydrogen atmospheric pressure test. The nozzle characteristics were compared and analyzed, and the results show that all nozzles performed well under base load conditions, with low NOx emissions and no flashback. Extreme conditions were also tested to check flame stability, such as the Lean blow out and the Flashback. The study concludes that the designed nozzles show promise for use in actual Full CAN combustors, and updates will be made to improve their shortcomings.

This study examines the influence of partial replacement of Co with Cu on isothermal transformation kinetics in 10Cr‐based heat‐resistant steels. Two kinds of heat‐resistant steels, having similar chemical compositions except for Co and Cu contents, are prepared and isothermally heat‐treated at 710–790 °C up to 240 h after austenitization. During isothermal heat treatment, austenite is decomposed via two different reactions, γ → α + M23C6 and γ → α; the cellular precipitation (γ → α + M23C6) nucleates at prior austenite grain boundaries or the interior of prior austenite grains and grows toward the interior of austenite, followed by γ → α transformation originating from C depletion in the remaining austenite. A time–temperature–transformation diagram exhibits that the partial replacement of Co with Cu not only decelerates the isothermal transformation kinetics but also lowers the nose temperature of transformation. The calculation of the driving forces for the successive reactions reveals that the increase of Cu content predominantly reduces the driving force for both γ → α + M23C6 and γ → α reactions, contributing to the lower nose temperature and sluggish transformation kinetics as Co is partially replaced with Cu.