Light Load Region Research Articles

A Dual-Bridge DC–DC Resonant Converter Using Extended PWM and Phase-Shift Control

To enhance the overall efficiency of a dual-bridge resonant converter, a new asymmetric pulsewidth modulation (PWM) control named extended pulsewidth modulation (EPWM) with both variable pulsewidth and variable symmetry is introduced in this article, which is applied to the high-voltage-side bridge of the converter and is combined with phase-shift control to form a 3-D gating scheme. A specified control strategy based on the 3-D gating scheme is then derived for the purpose of minimum tank current operation. Thanks to the flexibility brought by EPWM, full zero-voltage switching (ZVS) operation range is maintained as large as that of a conventional PWM-based minimum current trajectory, and only one switch loses ZVS at light load. The modulated voltage pulsewidth is kept at high level in a wide load range, which compromises the by-effect of high-order harmonics due to asymmetric modulation. Besides, the backflow power on both sides is almost minimized naturally. Therefore, the proposed control trajectory can have better performance in a light-load region than previous reported solutions. Experimental results prove the accuracy and effectiveness of the proposed minimum current operation with wide ZVS range and show the improvement of overall conversion efficiency.

Wide ZVS operation of a semi‐dual‐bridge resonant converter under variable‐frequency phase‐shift control

A secondary phase-shifted dual-bridge converter with semi-active rectifier is able to perform buck–boost dc–dc conversion with soft-switching. However, it can not maintain zero-voltage switching (ZVS) operation for all switches in a wide load range. Besides, the root mean square/peak tank current increases inversely with the decreasing of load in the light load region. To alleviate these problems and extend its load range, a hybrid varying-frequency phase-shift (VFPS) control is proposed to manipulate the power for a semi-dual-bridge converter with the primary half-bridge and secondary semi-active rectifier topology. Steady-state analysis of the converter under VFPS control is performed using the fundamental harmonic approximation approach. A detailed design procedure is given then to find a full ZVS trajectory with a fixed ZVS margin at light load. Experimental results proved that the VFPS control can effectively extend the operation range with full ZVS and maintain high efficiency at light load for the semi-dual-bridge resonant converter.

A Hybrid Converter for Improving Light Load Efficiency

In order to reduce power consumption of electronic equipment in stand-by mode, idle-mode and sleep-mode, a simple efficiency improvement technique for switching regulator in light load region is proposed. In this technique, under the light load, the small switching elements in a MOSFET driver circuit are used instead of the switching elements in a main regulator circuit to reduce driving losses. Of course, under the load heavier than light load, the MOSFET driver drives the switching elements in the main regulator circuit. The efficiency of a 2.5V/5A prototype buck converter is improved from 47.1% to 72.7% by using the proposed technique.

A Numerical Study of Three Dimensional Vortex Behavior of a Side Ported Rotary Engine.

This numerical study focuses on the three-dimensional vortical structure of a flow field inside a side-ported rotary engine. Since both two-dimensional numerical simulation and experimental visualization methods may not be applicable to side-ported rotary engine where the flow field inside is essentially three-dimensional, the authors have developed a three-dimensional computer simulation code based on the compressible Navier-Stokes equations. A Chakraverthy third-order TVD scheme devised in the code successfully calculates a flow field in a light load region at 3000 rpm, since the macroscopic stroke characteristics show appropriate behaviors. The velocity vector fields alone do not seem to provide fundamental images of the flow fields, thus characteristic vortex tubes are sought. Although it is not easy to extract vortex tubes closely surrounded by the moving boundary walls, they are capable of providing useful information which otherwise may not be given. The shapes and their change in vortex tubes, in fact, refine perspectives on the flow fields, and hence the effects of the intake flow and the rotor motion on the flow structure are well understood.

MHD直接発電の最大効率条件

Maximum efficiency condition of MHD power generation have been derived as follows:(1) Spacialy homogeneous distribution both of induced electro-motive-force and of the ratio of the applied magnetic induction to the density of a working fluid are required for irrespective of compressible or incompressible plasmas.(2) In case of incompressible plasmas, a homogeneous distribution of the magnetic induction is requested.(3) The magnitude of the required external loading at optimum and maximum efficiency power conversion is determined and it is proved that the optimum value of loading exists in a light load region.