No abstract

Abstract-This paper presents a primary-parallel secondaryseries multicore forward microinverter for photovoltaic ac-module application. The presented microinverter operates with a constant off-time boundary mode control, providing MPPT capability and unity power factor. The proposed multitransformer solution allows using low-profile unitary turns ratio transformers. Therefore, the transformers are better coupled and the overall performance of the microinverter is improved. Due to the multiphase solution, the number of devices increases but the current stress and losses per device are reduced contributing to an easier thermal management. Furthermore, the decoupling capacitor is split among the phases, contributing to a low-profile solution without electrolytic capacitors suitable to be mounted in the frame of a PV module. The proposed solution is compared to the classical parallel-interleaved approach, showing better efficiency in a wide power range and improving the weighted efficiency.

This paper proposes a novel modulation technique for the bidirectional operation of the Phase Shift Full Bridge (PSFB) DC/DC power converter. The forward or buck operation of this topology is well known and widely used in medium to high power DC to DC converter applications. In contrast, backward or boost operation is less typical since it exhibits large drain voltage overshoot in devices located at the secondary or current-fed side; a known problem in isolated boost converters. For that reason other topologies of symmetric configuration are preferred in bidirectional applications, like CLLC resonant converter or Dual Active Bridge (DAB). In this work, we propose a modulation technique overcoming the drain voltage overshoot of the isolated boost converter at the secondary or current-fed side, without additional components other than the ones in a standard PSFB and still achieving full or nearly full ZVS in the primary or voltage-fed side along all the load range of the converter. The proposed modulation has been tested in a bidirectional 3.3 kW PSFB with 400 V input and 54.5 V output, achieving a 98 % of peak efficiency in buck mode and 97.5 % in boost mode operation. This demonstrates that the PSFB converter may become a relatively simple and efficient topology for bidirectional DC to DC converter applications.

No abstract

Microcantilever based sensors are promising devices because they are fast, low cost, portable and allow measuring extremely small quantities of substances in gas or liquid phase that are not detectable by other methods. In this work we investigate the swelling and deswelling behavior of poly(hydroxyl ethyl methacrylate), PHEMA, films with three different average molecular masses deposited onto bare silicon microcantilevers, a hydrophilic substrate, and onto polystyrene (PS) coated microcantilevers, which is a hydrophobic substrate, under humidity cycles by monitoring the deflections resulting from differential surface stress. The results found in the present study demonstrate that the micromechanical response observed are related not only to the polymer molecular weight, but also to the polymer-interface phenomena and environment-polymer interface that can play a crucial role on the signal transduction. Ellipsometric measurements evidenced that the swelling of PHEMA films with intermediate molecular weight at 80% RH follows Fickian diffusion mechanism. Nevertheless, due to the weak optical contrast or film homogeneity shorter or longer chains than PHEMA-300 could not be investigated by ellipsometry. PHEMA films deposited onto PS surfaces presented dewetting, which limited the ellipsometric measurements. In comparison to ellipsometry, monitoring swelling behavior of PHEMA by nanomechanical responses is more advantageous because it is faster and less restricted.