Thomas Heckel

Characterization and application of 600 V normally-off GaN transistors in hard switching DC/DC converters

As GaN power devices emerge from research to industry, the characterization of these novel devices itself and its application in power electronic converters is essential. The purpose of this paper is to prove the capabilities of GaN technology using a novel 600 V normally-off GaN-on-Si transistor which shows no dynamic behavior of its on-resistance. A hard switching DC/DC converter prototype reveals efficiencies up to 99.3 % and switching frequencies up to 1 MHz incorporating a high power density up to 28 kW/l.

Implementation of simultaneous energy and data transfer in a contactless connector

This paper presents a contactless near field energy and data transfer system, which uses one common pair of coils for both transmission purposes. Though a contactless connector for harsh environments proves an exemplary application, the concept can be adapted to several other applications. The challenge is to transmit the data simultaneously to a large energy signal. The system concept, simulation, as well as measurement results of a hardware demonstrator will be presented in this paper. It will be shown that a robust data transmission system can be realized featuring superior SNR and nearly noise free operation even with a simultaneous energy transfer of several kilowatts.

Fundamental efficiency limits in power electronic systems

In this paper, the efficiency limits of power electronic converters are investigated from a semiconductor point of view. The approach is presented on the example of a hard switching half bridge while taking Si, SiC and GaN devices into account. Beside parasitic effects of the semiconductors itself, further converter non-idealities and limits from a thermal point of view are discussed. All in all, the obtained results act as a design guideline and allow for an easy comparison of different semiconductor technologies.

Using SiC MOSFET’s Full Potential – Switching Faster than 200 kV/μs

SiC-MOSFETs are available since several years, but unlike SiC diodes they have not arrived in the mass market yet. The main reason is that the higher costs do not get compensated by the technical advantages in common applications. This lack is not only caused by the SiC-MOSFETs itself, but also by the packaging and the gate drivers. Consequently the main challenge for getting SiC-MOSFETs to a wider acceptance by application engineers is to show how all benefits of the new technology can be used. This paper demonstrates how SiC-MOSFETs can be operated in a standard half bridge application with exceptional switching speeds of less than 4 ns, resulting in slopes of more than 200 kV/μs and lowest possible switching losses. Previous publications have claimed to use “the full potential of the SiC devices for power conversion applications” achieving switching times of 20 ns [1].

SiC MOSFETs in Hard-Switching Bidirectional DC/DC Converters

In this study, the necessity and beneficial characteristics of SiC power devices for novel power electronic applications are shown from an application point of view. The body diode properties of state of the art 1200 V SiC MOSFETs are discussed and the dependencies of switching speed are derived. Furthermore, the calculation of the fundamental efficiency limit of 99.67 % at the example of a bidirectional DC/DC converter operating at 100 kHz is shown.

Inductive power transfer system with a rotary transformer for contactless energy transfer on rotating applications

This paper examines an inductive power transfer (IPT) system with a rotary transformer as an alternative solution to slip ring systems for a contactless energy transfer to rotating equipment. A prototype system is set up, consisting of a rotating ball bearing shaft and an exemplary sensor circuit mounted on the shaft. Three possible transformer configurations are analyzed theoretically and experimentally regarding the self-inductance, the coupling factor and the losses in the litz wire. To utilize the intrinsic stray inductances of the rotary transformer, a series compensated resonant converter is implemented for the prototype system.

Influence of the junction capacitance of the secondary rectifier diodes on output characteristics in multi-resonant converters

Multi-resonant converters like the CLLLC topology are known for their outstanding efficiency and high power density. Little information has however been published about the influences of secondary side diode junction capacitances on the output characteristics of the resonant converter. This paper presents a detailed analysis of these influences in the inductive working range and reviews practical design considerations of the converter. Therefore, experimental results of an inductive power transfer system, using a CLLLC resonant topology, are compared to theoretical time domain solution, showing significant effects of different semiconductor materials and devices on output power. These effects will be discussed and explained in detail by using measured key waveforms.

Analytical Model for the Influence of the Gate-Voltage on the Forward Conduction Properties of the Body-Diode in SiC-MOSFETs

In this study, the influence of the gate-source voltage on the forward conduction properties of the body-diode in SiC-MOSFETs is demonstrated experimentally and analyzed by numerical simulations. Thereby, it can be figured out that the conduction properties of the body-diode strongly depend on the operational state of the MOS-capacitor. In depletion case, the current via the body-diode is dominant, whereby in accumulation and inversion mode the current mainly flows through the MOS-channel.

Inductive high data rate transmission for bearing systems

This paper describes a wireless transmission system for fast moving objects to transmit 20 W power and data simultaneously on ball bearing systems. Data communication using inductive transmission technology at 13.56 MHz has to deal with strong cross-interference due to the power link signal. The surrounding material influences the antenna characteristic and the signal strength. The main challenge was the design of the coil in respect of the size and positioning, as well as tolerance against displacement. In this paper, the antenna design will be presented in detail by using simulations and measurements.

Temperature and Electrical Field Dependence of the Ambipolar Mobility in N-Doped 4H-SiC

In this study, we present results on electrical characterization of bipolar pn-diodes to investigate the temperature and electrical field dependent behavior of ambipolar mobility in n-doped 4H-SiC. Therefore, static current-voltage measurements to calculate the specific differential resistance and dynamical reverse recovery measurements to determine the mean carrier concentration were carried out for different temperatures and forward current densities. The specific differential resistance of the drift layer decreased from 10 mΩcm2 at 80 Acm-2 to 6.6 mΩcm2 at 180 Acm-2, whereas the mean carrier concentration only increased from 4.1015 cm-3 to 8.1015 cm-3, indicating a decreasing ambipolar mobility. The calculated reduction of the ambipolar mobility from 800 cm2V-1s-1 to 650 cm2V-1s-1 in dependence on the current density has to be attributed to an increasing electric field from 150 Vcm-1 to 250 Vcm-1 and increasing carrier scattering due to higher carrier concentrations. For example, at a constant conduction current density of 160 Acm-2, the ambipolar mobility decreases from 710 cm2V-1s-1 at 300 K to 650 cm2V-1s-1 at 450 K.