Refine
Year of publication
- 2020 (9) (remove)
Document Type
Language
- English (9) (remove)
Has Fulltext
- no (9)
Is part of the Bibliography
- no (9) (remove)
Keywords
Institute
- Fakultät für Ingenieurwissenschaften (9) (remove)
Design of a Low Multi-Loop Inductance Three Level Neutral Point Clamped Converter with GaN HEMTs
(2020)
This work shows a numerical and experimental analysis of a Neutral-Point-Clamp (NPC) three level inverter featuring an ultra low inductance printed circuit board (PCB) design in consideration of the mutual inductive and capacitive couplings. The commutation loops in this design are found to be strongly dependent on the vertical thickness of the used prepregs and the core. For vertical thicknesses ≤ 100 μm capacitive coupling must be taken into account in the switching cell design. Experimental measurements of a test set-up with a total PCB thickness of 400 μm results in commutation loop inductances from 1.4 nH up to 3.1 nH. In this set-up, switching tests without external gate resistor showed only a maximum voltage overshoot of 7% at 800 V. Based on a numerical analysis of the NPC cell we propose a further switching performance improvement with significant smaller parasitic inductance due to the application of novel printed circuit technologies such as the integration of bare dies into the printed circuit board or polyimide as an interlayer dielectric material.
The dynamic behavior and position stability of servo drives are influenced by many parameters. One major influencing parameter is the pulse width modulation (PWM) frequency. With inverters based on wide bandgap semiconductors, the PWM frequency can be increased. This enables a substantial increase in the current control bandwidth. The paper focuses on the influence of the PWM frequency on the dynamics of control loops and position stability, which are derived from theoretical correlations. The theory is verified using a test bench for high dynamic and position stability. The test bench is equipped with a voice coil motor and power electronic with gallium nitride (GaN) power semiconductors for switching frequencies of 100kHz and over. The achieved position stability, measured with a laser-based comparator at the tool center point, is lower than "+-1nm" with a standard deviation of "0.16nm" at a PWM frequency of "f_PWM=100kHz".
We present a numerical and experimental design study for reducing conducted common mode noise for frequencies below 10MHz generated in switching cells comprising sub-nH commutation loops. Compared to conventional methods of adding external gate resistors our approach does not degrade efficiency. A parallel plate loop design (characterized by a minimum loop inductance and small board area usage) is found suboptimal in terms of conducted EMI compared to a micro-strip line loop geometry. The net ground impedance rather than the net ground inductance is found to mainly contribute to the observed EMI noise.
A DDR3 SDRAM test setup implemented on the Griffin III test system from HILEVEL Technologies is used to analyse the row hammer bug. Row hammer pattern experiments are compared to standard retention tests for different manufacturing technologies. The row hammer effect is depending on the number of stress activation cycles. The analysis is extended to an avoidance scheme with refreshes similar to the Target Row Refresh scheme for the DDR4 SDRAM technology.
A novel approach to optically distinguish plastics based on fluorescence lifetime measurements
(2020)
A novel approach to optically distinguish plastics based on fluorescence lifetime measurements
(2020)
In medical and biological research, fluorescence lifetime measurements and fluorescence lifetime imaging is already a part of the standardized analysis procedures. As first investigations have shown, polymers can be identified using fluorescence lifetime imaging and an evaluation algorithm. Thus, this contribution pursues a novel approach for the direct differentiation of four polymers with fluorescence lifetime imaging. Therefore, the evaluation algorithm is extended to compare several fluorescence lifetime images to prove that a distinction is possible.
Plastic waste is one of the biggest growing factors contributing to environmental pollution. So far there has been no established method to detect and identify plastics in environmental matrices. Thus, a method based on their characteristic fluorescence behavior is used to investigate whether plastics can be detected and identified in tap water under laboratory conditions. The experiments show that the identification of plastics as a function of water depth is possible. As the identification becomes more difficult with higher water depths, investigations with a highly sensitive imaging method were carried out to obtain an areal integration of the fluorescent light and thus better results.