An efficiency-oriented two-stage optimal design methodology of high-frequency LCLC resonant converters for space travelling-wave tube amplifier applications

The high-frequency LCLC resonant converters are widely used in the two-stage power converter as a dc transformer for the space travelling-wave tube amplifier applications. In the two-stage power converter, since the output voltage is controlled by a preregulator, which is the first stage, the main functions of the high-frequency LCLC resonant converter, which serves as the second stage, are to boost the input voltage and to provide galvanic isolation while keeping high efficiency. As boosting the input voltage and providing galvanic isolation can be achieved by the transformer, achieving high efficiency is most challenging. Previous studies on the LCLC resonant converter mainly focus on reducing the switching loss. However, in addition to the switching loss, the total power loss of the LCLC resonant converter contains driving and conduction loss of the main switches; core loss, copper loss, and dielectric loss of the transformer; and the conduction loss of the rectifiers. As a result, low switching loss cannot guarantee the high efficiency of the LCLC resonant converter. To solve this problem, in this paper, an efficiency-oriented two-stage optimal design methodology of the LCLC resonant converters is proposed. In the first stage, the optimal parameters of the LCLC resonant converter, which aims at minimizing the total power loss of the converter, are found from the proposed genetic algorithm + particle swarm optimization algorithm. After that, in the second stage, a single-layer partially interleaved transformer structure is proposed to realize the optimal parameters. After the transformer design is finished, the optimal LCLC resonant converter is built. The proposed efficiency-oriented two-stage optimal design method and the transformer structure are validated by simulations and experiments.Ministry of Education (MOE)Nanyang Technological UniversityThis work was supported in part by Singapore ACRF Tier 1 Grant RG 85/18, and in part by the start-up grant (SCOPES) of Prof. Xin Zhang

Porous Media Thermoacoustic Stacks: Measurements and Models

The present research analyzes random porous thermoacoustic stack systems analytically, experimentally, and numerically with a primary objective to develop a comprehensive analytical porous media modeling for random porous (such as Reticulated Vitreous Carbon (RVC) foams) environment. Mathematical models are developed for flow, thermal, and energy fields within the random porous medium stack. The Darcy and Brinkman-Forchheimer-extended Darcy models are used for modeling the momentum equation and local thermal equilibrium assumption between the porous matrix and trapped fluid in the void space for energy equation. The expressions of temperature, energy flux density, and acoustic work absorbed or produced by a thermoacoustic device are compared with existing literature and observed good agreements. After obtaining the flow and thermal fields’ information, the present study examines the entropy generation distribution within the stack. One important item revealed in this study is that entropy generation inside the porous medium completely follows the trend of the imaginary part of Rott’s first function profile. Another major contribution of this research is to identify the location of maximum entropy generation which is identical to the location of maximum thermoacoustic heat and work transport. The expression of Nusselt number for steady flow cannot be used in oscillatory random porous medium because of the phase difference between the temperature gradient at the wall and the temperature difference between the wall and the space averaged temperature. The present research experimentally examines novel stack configuration by considering “alternating conducting and insulating materials” as stack in thermoacoustic devices. The objective of considering such stack arrangement is to reduce the conduction heat transfer loss from the hot end of the stack to the cold end, thereby increasing the performance of the stack. Eight different heterogeneous stack arrangements are studied in this research. The performance of the heterogeneous stack arrangement is compared with the typical homogeneous stacks. This research shows that heterogeneous stacks can be used in thermoacoustic devices particularly in small (millimeter) scale thermoacoustic devices. Numerically the present study investigates the influence of working fluid, geometric, and operating conditions on stack performance by solving the full Navier-Stokes, mass, energy equation, and equation of state