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A gate drive circuit for gallium nitride (GaN) enhancement mode (e-mode) transistors is presented, which avoids parasitic turn-on of the power devices in the halfbridge configuration. New e-mode GaN devices turn on at very low threshold voltages between 1V and 2V. This makes the transistors highly sensitive to spurious turn-on and thus reduces the required safety margin of the gate drive signals. To avoid this parasitic turn-on, a very low gate loop impedance is required. This prevents the halfbridge against bridge shorts during the switching events and guarantees stable gate drive control with increased switching efficiency. The new gate drive circuit is developed in a SPICE simulation environment and verified in a prototype setup by a double pulse test. The simulation matches very well with the experimental result and demonstrates the suppression of parasitic semiconductor turn-on with the proposed gate drive. Furthermore the dissipated switching energy is reduced, compared to a standard gate drive circuit. High DCDC converter efficiency of 98.67% at 1kW output power is achieved by using the driving circuit for a buck converter prototype with 200kHz switching frequency.
An accurate SPICE model is proposed in this paper to calculate the power losses of high voltage converter systems. This supports power circuit optimization in the very first design stage. The parasitic package inductances and the nonlinear voltage dependent semiconductor capacitances are taken into account. In addition the high frequency behavior of the power inductor is investigated. A detailed loss breakdown is done to analyze the main sources of power loss and their physical reasons. The simulation results of the converter waveforms and of its efficiency match very well to the experimental results. The prototype boost converter shows a top efficiency greater than 98.3 % at a switching frequency of 1 MHz and an output voltage of 400 V at the maximum output power of 1 kW.
A Parametric Layout Study of Radiated Emission from High-Frequency Half-Bridge Switching Cells
(2016)
We present a numerical modeling study of radiated emission from half-bridge switching cells based on the method of moments (MoM). A low loop inductance cell design enables high-speed switching of power semiconductors which is demonstrated on a prototype circuit. The layout is further optimized for low radiated emission by variation of the heat sink placement. This is achieved by the heat sink attached to the phase terminal. The performance of the structure in terms of loop impedance, electric field radiation and sensitivity to cable attachments are numerically studied. Emission peaks arising from loop resonances can be reduced by over 20 dB with damping elements in the switching cell. The improved EMI performance of the proposed structure is attributed to decoupling of the loop current from the heat sink structure.
Outdoor or just on site analyzes of photovoltaic modules can offer some advantages in comparison to indoor Lab studies. In this way the electrical performance is monitored and logged under natural operating conditions in full range of irradiation and temperature. The entirety of monitored IV data allows deriving low-light characteristics of electric parameters, temperature coefficients and root cause analysis for possible degradation. We apply so-called self-reference algorithm in order to increase the accuracy of analysis. The improved precision is due to application of effective acting irradiation and effective temperature instead of externally measured data. Effective irradiation is determined in self-referencing scheme: the short circuit current of the module is assigned to the irradiation. This assignment has to be calibrated, preferably at standard test conditions for irradiation. In this contribution we demonstrate a process of precise measurement of Isc under clear-sky outdoor conditions and the determination of the short circuit current for STC. The measurement method avoids errors by spectral deviations with respect to AM 1.5G spectrum, by optical reflection losses for high angles of incidence and errors by high albedo impact. In particular we investigate comparatively a CdTe module under outdoor conditions and by means a calibrated indoor Lab flasher.
Outdoor or just on site analyzes of photovoltaic modules can offer some advantages in comparison to indoor Lab stud-ies. In this way the electrical performance is monitored and logged under natural operating conditions in full range of irradiation and temperature. The entirety of monitored IV data allows deriving low-light characteristics of electric parameters, temperature coefficients and root cause analysis for possible degradation. We apply so-called self-reference algorithm in order to increase the accuracy of analysis. The improved precision is due to application of effective acting irradiation and effective temperature instead of externally measured data. Effective irradiation is determined in self-referencing scheme: the short circuit current of the module is assigned to the irradiation.
Laminated veneer lumber poles for temporary soil nailing ‐ investigation of material properties
(2016)
Within a current research project at Rosenheim University of Applied Sciences and Graz University of Technology the possibilities of using beech wood laminated veneer lumber poles as soil anchors for temporary soil nailing systems are investigated. Therefore tensile and bending properties of laminated veneers with high moisture and permanent cement contact concerning the influence of veneer bending rectangular to the fibre are determined. For investigation of material properties under different climate conditions tensile tests on small and faultless single beech wood veneers as well as tensile tests on 6 layered 3 mm samples and 9 layered 2 mm samples were carried out.
Therefore all samples were stored in extreme climate conditions like high moisture content and permanent cement contact. Six layered samples with 3mm thick veneers show a slightly higher strength and stiffness under dry conditions as well as at a moisture content of the samples above fibre saturation. A strength reduction factor concerning temporary geotechnical applications is suggested which considers the influence of long term loading, veneer bending, water saturation and
cement destruction on tensile properties of laminated veneer lumber poles.
Within a current research-project the possibility of using laminated veneer lumber beech wood poles as temporary soil anchors in foundation engineering is investigated. Within this project adhesive properties of laminated veneer lumber beech wood poles are determined. For
use in temporary ground applications the influence of veneer bending, veneer thickness and intensive cement contact is concerned. As standard version two different adhesive systemsmelamine formaldehyde resin (MUF) and a 1-component polyurethane adhesive (PUR) were investigated and compared.
Melamine formaldehyde resin glued samples with 3 mm thick veneers and 1.0N/mm² press force show a higher tensile shear strength but also a higher adhesive failure percentage than polyurethane glued samples. In case of melamine formaldehyde resins the closed time has a great influence on bond line quality. A long closed time reveals a low penetration of adhesive in the cells and a low embedding on the wood surface. For curved structures best results were achieved with a bonding pressure of 1.0 N/mm². A significant difference in strength between the concerned MUF and PUR adhesive system was not recognized.