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Institute
A mechanically tunable planar single-turn inductor in air is proposed. The bistable flexible deflection of axially compressed wire segments is used for variation of the loop area of regular polygonal loop inductors. We present analytical expressions for the loop inductance and confirm the theoretical findings by magneto-quasi-static field simulation on exemplary polygonal circuits.
The variation of the contact impedance of adhesive conductive EMI shielding tapes under high temperature storage (HTS) of 110degC is investigated. The adhesive tapes under test are implemented as signal return paths in microstrip lines. Changes in the ground plane impedance by adhesive deterioration are analyzed by S-parameter measurements from 1MHz to 3GHz. A circuit model for contact impedance degradation is proposed and applied in simulation of board level shielding. Contact resistance and contact capacitance are found to increase significantly after 2400h, causing a declined magnetic field shielding effectiveness by 30 dB below 500 MHz.
Enhanced inductive power transmission (IPT) between coaxially arranged circular coils is introduced by time-modulation of the mutual inductance. This modulation is accomplished by coherent switching of the short circuit current induced in a third loop. An analytical circuit model supporting the design for future time-modulated IPT systems is derived. We demonstrate an increase in load rms-voltage by 13% (28% gain in power) compared to an unmodulated transfer on an experimental system operating at fundamental frequencies ranging from 40kHz to 500kHz.
A Planar Magneto-Inductive Device with Modulated Mutual Inductance for Wireless Power Transmission
(2023)
A Magneto-Inductive Wave (MIW) structure for wireless power transfer (WPT) is proposed with switchable mutual inductance between neighbored coupling coils. Orthogonally placed switchable short circuit loops are added in order to modulate the wave propagation properties of the MIW structure without changing the resonance frequency. We derive an analytical model based on lumped circuit analysis for the MIW waveguide and successfully evaluate the theoretical findings by circuit modeling and field simulation. We demonstrate switchable, i.e. addressable, guided wireless power transfer along an experimental MIW structure at a resonance frequency of 20.5 MHz.
We introduce a quick and accurate quasi-static magnetic field scanning technique by employing a progressive sampling method in an unconfined input space. The proposed
machine learning algorithm is tested against uniform sampling on a printed circuit board test structure. We prove allocation of multiple, separated regions with predefined tangential field strengths at MHz frequencies. The feasibility of equivalent magnetic dipole source modeling based on a small number of samples is demonstrated. Compared to uniform testing, progressive expansion sampling detects contours of given field limits in less than 3% of the reference measurement time.
The automotive industry is pushing power electronic packaging to higher operating and heatsink temperatures while still requiring very high power densities due to limited space. Currently, the power electronics that is implemented within the engine compartment of the vehicle must operate with heatsink temperatures of approximately 85/spl deg/C and this temperature can be expected to increase to 125/spl deg/C in the near future. The high temperature operation of the power electronic structure is fundamentally limited by the employed materials maximum temperatures. A packaging concept is introduced that describes a structure realisation that enables the materials to operate at high ambient temperatures without exceeding their individual maximum temperatures. This in turn allows the complete power electronic structure to operate at a higher system temperature. In this paper, the packaging concept that can be used to meet these difficult requirements of high temperature and high power-density is introduced, discussed and implemented. Two case studies are considered and implemented to illustrate the packaging concept.
A compact and high-reliable converter design for an Integrated Starter Generator is presented. The concept is based on integration of the power switches with both the cooling system and the DC link capacitor, which optimizes the thermal management and minimizes inductive and conductive losses. The materials and joining technologies are selected in such a way that the converter can be operated up to 125 C ambient temperature. Therefore, the water cooling system of the combustion engine can directly be used. The paper further reports on circuit simulation results verifying the converter design and on first electrical measurements obtained on a functional prototype operating under normal load conditions (6kW rated power).
Built-in EMC in der Aufbau- und Verbindungstechnik am Beispiel des integrierten Startergenerators
(2002)
We present a fast and accurate measurement technique for quasi-static magnetic fields by employing a progressive sampling method in an unconfined input space. The proposed machine learning algorithm is tested against uniform sampling on printed circuit board test structures and a buck converter. We prove allocation of multiple, separated regions with predefined lateral field limits at MHz frequencies. The feasibility of equivalent magnetic dipole source modeling based on a small number of samples is demonstrated. Compared to uniform testing, progressive expansion sampling identifies contours of given field limits in less than 3% of the reference measurement time.
Reliability analysis of power MOSFET’s with the help of compact models and circuit simulation
(2002)
High temperature reliability on automotive power modules verified by power cycling tests up to 150°C
(2003)
Validation and calibration of Electrothermal Device Models Using Infrared Laser Probing Techniques
(1998)
We present inductive power transfer (IPT) with a half-bridge converter based on differential relaxation self-oscillation. The oscillation dynamics of the converter automatically adapts to variation in the inductive coupling link and changes in the load, respectively. Design equations based on theoretical circuit analysis reveals a high power transfer efficiency (>90%) for alteration of coupling distance in the strong coupling regime. A prototype system employing GaN-HEMTs confirms the theoretically predicted characteristics of the proposed circuit.
We present a novel differential relaxation oscillator for inductive power transfer. The proposed oscillator offers an automatic adaption of the oscillation period to a change in the power link impedance, which ensures a high efficient operation for variable loads and coupling factors. A detailed circuit model of the self-oscillation system is provided with analytical design equations. We find a large self-oscillation range for variable coupling factors and loads. The theoretical results are confirmed by circuit simulation and measurements carried out on a low-power demonstrator system. We demonstrate non-resonant and robust self-adaption of the relaxation oscillator to coupling factors ranging from k=0.6-0.9.
In this research we present a short distance capacitively coupled wireless power transfer (WPT) system with a self-oscillating half-bridge converter, which uses a positive feedback signal from the WPT system. By this novel implementation we find additional features of the system compared to linear amplifier based systems. With the DC bias voltage supplying the power converter, we achieve a controllable output power, tunable self-oscillation frequency and extension of the self-oscillation range. We present the analytical expressions for the converter waveforms. The theoretical analysis is confirmed by circuit simulation results and measurements on a prototype featuring a half-bridge converter with Gallium-Nitide (GaN) HEMTs. We achieve a system efficiency of 93% at a load power of 83W and 150kHz switching frequency.
We present the design of a half-bridge converter
for a capacitively coupled wireless power transfer
system. The load signal acts as a positive feedback
signal for a self-oscillation circuit which generates the
driving gate signals for the converter. Our research
reveals a robust wireless operation for a large range
of load resistors and coupling capacitors. Based on an
electric network analysis we obtain design criteria for
self-oscillation and for the power transfer. The theoretical
predictions are confirmed by circuit simulation
and measurement results on a converter prototype with
GaN-HEMTs. We report on a transfer efficiency of 92%
for a power greater than 50W at a switching frequency
of 300kHz and 200V DC link voltage.
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.
We present low-cost, high-efficient electromagnetic coupling between open ring geometry and a so-called butterfly structure on standard printed circuit boards (FR4) for the purpose of short range wireless data and power transfer at an UHF resonance frequency of 868 MHz. The components of the transfer system are characterized by simulation and experiments in terms of associated scattering parameters. Characterizing the efficiency of the coupled resonators, RF signal power transmission is examined for high power transfer as well as for low power DC supply utilizing a voltage doubler rectifier. With an enhanced butterfly structure coupler, unmodulated RF power transmission of 17.3 W is achieved with an efficiency of more than 95%. Furthermore, signal transmission of Pulse-Width-Modulated (PWM) signals with frequencies up to 5 MHz is demonstrated.
Wear-out failures of electrolytic capacitors in single phase power factor correction circuits are investigated in this study. A probabilistic model based approach for temperature driven capacitor degradation is chosen to analyse the probability of failure of the output capacitor bank. Different design strategies are proposed and evaluated in terms of reliability. Parametric variation of capacitor bank designs provides influential effects on system volume, cost and reliability which is modeled for a sample size of 1000 power supply units.
The recent developments in power semiconductor devices and increasing demands on reliability as well as on operation performance require innovative package technologies. Such a novel package technique based on a Planar Interconnect Technology (SiPLIT®) for power modules is introduced in this work. This package features thick Cu interconnects on a high-reliable insulating film for power semiconductor chip top contacts. Due to the conductor structure and contact technology, on-resistance and stray inductances are very low compared to state-of-the-art Al wire bonds. In addition, large area contacting improves the power cycling capability and surge current robustness significantly. These remark-able properties have been verified on several prototype modules where the manufacturing process has also been optimised in terms of cost-effectiveness, system integration and maturity for series production.
Innovative Leistungsmodule
(2011)
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.
Wide-bandgap semiconductors such as Silicon Carbide (SiC) or Gallium Nitride (GaN) enable fast switching and high switching frequencies of power electronics. However, this potential can not be exploited due to limitations caused by parasitic elements of packaging and interconnections. This paper shows a possibility to minimize parasitic elements of a half-bridge switching cell with 650 V GaN dies integrated into a printed circuit substrate. A sub-nH commutation loop of 0.5 nH inductance gives superior switching characteristics compared to circuits with packaged dies. Simulation and experimental results of an inverse double pulse test confirm our expectations. This study further reveals additional benefits of the proposed technology in terms of mechanical stability and thermal interfacing to heat sinks compared to circuits with packaged dies.
Power cycling and temperature endurance test of a GaN switching cell with substrate integrated chips
(2019)
We present a reliability study of a half-bridge switching cell with substrate integrated 650 V GaN HEMTs. Power Cycling Testing with a ΔTj of 100 K has revealed thermo-mechanically induced failures of contact vias after more than 220 kcycles. The via failure mode of contact opening is confirmed by reverse-bias pulsed IV-measurements to be primarily triggered by a ΔTj imposed thermal gradient and not by a high Tj. The chip electrical characteristics, however, remained unaffected during Power Cycling. Furthermore, a High Temperature Storage test at 125 °C for 5000 h has shown no changes in the electrical performance of substrate integrated GaN HEMTs.
This paper proposes an ultra-low inductance half-bridge switching cell with substrate integrated 650V GaN bare dies. A vertical parallel-plate waveguide structure with 100 μm layer thickness results in a commutation loop inductance of 0.5 nH resulting in a negligible drain-source voltage overshoot in the inductive load standard pulse test. On the other hand reliable circuit operation requires an assessment of the isolation strength of the thin dielectric layer in the main commutation loop, because critical high local electric fields might occur between the pads. Measurements of the dielectric breakdown voltage followed by a statistical failure analysis provide a characteristic life of 14.7 kV and a 10% quantile of 13.5kV in the Weibull fitted data. This characteristic life depends strongly on the ambient temperature and drops to 4.1kV at 125°C. Additionally, ageing tests show an increasing in dielectric breakdown voltage after 500h, 1000h and 2000h at 125°C high-temperature storage due to resin densification processes.
Gallium Nitride (GaN) semiconductor devices are promised to be a good alternative to Silicon (Si) semiconductors in future motor inverters for variable frequency drives (VFDs). They combine low on state resistance and low switching losses with a high blocking voltage capability. Compared to actual inverters based on insulated gate bipolar transistors (IGBTs) the pulse width modulation (PWM) frequency for efficient operation can be increased by a factor of 5 to 10, extending the PWM frequency range up to 500 kHz. This allows the use of motor filters with small component size. As a result, high motor efficiency, low torque ripple, high control bandwidth and nearly ideal sinusoidal output voltages are achieved. Therefore this inverters can be used for high speed spindle motors and dynamic servo drives. This paper focus on the design of a hybrid sine wave filter consisting of an analog and a digital part. The filter is optimized to achieve low power loss and high current control bandwidth. A 3-phase GaN motor inverter operating at 200 kHz PWM frequency at 400 V DC-link voltage verifies the system design.
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.
Increasing the switching frequency has been one of the most beneficial advancements in modern power electronics. This trend has been enabled by progress in power semiconductors resulting in increased power densities, efficiencies and control dynamics. The aim of this study is to analyze the influence of three different circuit carrier technologies on switching power loss of 650 V hardswitching GaN devices. Limitations and solutions for half-bridge circuits operating at MHz-switching are investigated by modeling and experiments on a prototype.
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.
Recent development of GaN power transistors with blocking voltages up to 650V enables novel power electronics applications with outstanding performance in high-frequency operation. This paper demonstrates a class E power amplifier with 13.56MHz switching frequency for inductively coupled DC power supplies. Continuous wave output power up to 200W is achieved with 95% Power Added Efficiency (PAE).
Increased productivity in industrial processes can be achieved by dynamic and accurate positioning of servo drives. Therefore, improvement of servo drive dynamics using latest technologies in the key components such as inverter, control system and position measuring device are investigated. Using Gallium Nitride (GaN) or Silicon Carbide (SiC) semiconductors for motor inverters enables energy efficient operation up to pulse width modulation (PWM) frequencies of 500 kHz. This allows motor filters with small component sizes. As a result, high motor efficiency, low torque ripple, high control bandwidth and almost ideal sinusoidal output voltages are achieved. Experiments on a 200 kHz Gallium Nitride inverter with sine wave motor filter show a current control loop bandwidth of 3.2 kHz and almost ideal sinusoidal phase voltages. The achieved bandwidths of the speed and position control loops are 318 Hz and 106 Hz, respectively.