Hybrid-switching asymmetrical half-bridge flyback DC-DC converter
This paper proposes a hybrid-switching technique for asymmetrical half-bridge flyback converter. In this topology, the duty loss can be minimized because the active switches can achieve zero-voltage-switching (ZVS) and the output diode can be turned off at zero current, which result in higher efficiency, higher power density and universal input voltage range (90-264V). Moreover, this technique doesn't require any addition of components into the original topology and still employ the fixed frequency PWM, therefore the control method is simple and straightforward, while still being highly reliable.
Analysis and design of high frequency asymmetrical half bridge flyback converter
The asymmetrical half bridge flyback converter is gaining popularity because it can achieve ZVS operation. However, the relationship between voltage transfer ratio and duty cycle is nonlinear in the condition of high switching frequency and small blocking capacitor. It is improper to use the linear model to guide the design of asymmetrical half bridge flyback converter. This paper deduces a steady-state voltage transfer function of the converter at high frequency, and the effect of load is also taken into consideration. According to the steady-state voltage transfer function, the characteristics of voltage transfer ratio and maximum duty cycle can be determined. Finally, a 19 V/6 A, 250 kHz prototype is designed and built to verify the analytical results. The experimental results indicate that, compared to the linear model, the asymmetrical half bridge flyback converter designed according to the voltage transfer function can be controlled more accurately and has significant merits at high frequency.
Damage initiation and propagation in composite shells subjected to impact
Abstract The paper investigates the impact-induced damage initiation and propagation for laminated composite shells under low-velocity impact. A three-dimensional eight-node non-conforming element is described to analyze interlaminar stress distribution, and progressive failure. The damage analysis is performed by using Tsai–Wu quadratic failure criterion, Tsai’s damage modes and an additional delamination formula at all Gaussian points. The damage modes considered are matrix cracking, fiber breakage and delamination. The progressive failure is expressed by reducing stiffness of the material at all failed Gaussian points. Special attention is centered on curved laminates. Impact energy threshold for the onset of damage and transient damage size are predicted for composite shells. The analyses of the flat and curved laminates are compared for discussing their different damage mechanism. In addition, the influence of the stacking sequence, the thickness and the radius of curvature on damage behavior of composite shells are studied.