Hoffmann, Klaus

A dynamical impedance analysis of complex electrical aerospace systems during operation can provide detailed information for efforts to further enhance system stability and reliability. As conventional single-tone impedance measurements are relatively slow compared to possible system state changes, a pulsed method using a synthesised stochastic multitone signal is proposed. This method is validated for a passive permanent magnet synchronous motor through a result comparison with an RF I-V impedance measurement. Then it is applied to an active DC- DC converter to highlight the detection of impedance changes due to the switching of the involved transistors, impossible to detect with conventional impedance measurement methods. It will be discussed how this method can be further adapted to overcome currently existing practical limitations and how it can be optimised for other electrical systems of interest.

This paper presents the degradation of 1200 V Siliconcarbide (SiC) MOSFETs in regard to the influence of different gamma radiation doses (γ-radiation). The impacts of four distinct γ-radiation doses (300 Gy, 200 Gy, 100 Gy and 50 Gy) were examined. The analysis was conducted using four different MOSFETs from several manufacturers, all of them in the TO263-7 package. They belong to the same voltage class with similar on-state resistance but varying technologies. The primary indicators for degradation analysed in this study are the threshold VGS(th) and the breakdown voltage VDSS(BR).

High bandwidth current sensors are needed to capture the fast switching transients of modern wide-bandgap semiconductor switches made from GaN and SiC. This work evaluates the usage of novel current sensors such as the M-Shunt and the second-generation Infinity Sensor for their ability to accurately resolve switching transients in the range of nanoseconds in high-current applications. Important metrics include: high bandwidth, low insertion inductance, small size and DC-capability. Measurement results are compared to established current sensors (Rogowski coil and coaxial shunt). Double pulse tests in an NPC inverter application were performed to test the sensors up to currents of 400 A.

The conducted electromagnetic interference (EMI) caused by a DC-DC power converter interfacing an automotive electric battery and the 48 V board grid can eventually affect the operation of the battery management system at the battery side of an electric vehicle or could transfer emissions to the board grid, where the conducted and radiated EMI originating from the converters could influence the signal electronics of automotive components. This work takes into account hardware setups of two different converter topologies: a phase-shifted full-bridge (PSFB) and a two-phase interleaved buck (TPIB) converter, both for up to 3 kW power and 400 V to 48 V voltage conversion. An analysis of the conducted and radiated emissions for half-load and full-load conditions is performed in buck operation mode. The results indicate the TPIB-topology having higher radiated emissions, higher differential mode emissions, but lower common mode emissions than the PSFB-topology.

This study investigates the reverse recovery behavior of Silicon Carbide (SiC) Merged-PiN-Schottky (MPS) diodes, analyzing the effects of case temperature, switching speed and turn-off currents. The diodes share the same die technology but differ in current ratings and package types. Measurements assess both the influence of packaging on switching behavior and the impact of internal charge carrier dynamics at different operating points. The results show that the bipolar charge contribution to the reverse recovery charge increases significantly with higher currents and temperatures, leading to more pronounced switching effects. However, up to a certain turn-off current, unipolar charge remains dominant, even at high temperatures, resulting in minimal impact on switching behavior. Package inductance, originating from lead and bond-wire contributions, affects voltage overshoot and oscillations at the die within the package but causes only minor differences in switching characteristics between the investigated packages when the printed circuit board (PCB) remains unchanged.

High voltage (HV) isolation in auxiliary power supplies (APS) has been most commonly achieved with the help of transformers. It has been mandated by standards to have sufficient clearance and creepage for such HV designs, which often increases the APS volume. For low power HV applications, for example, in isolated gate driver units, replacing toroidal cores with planar transformers can help reduce both the volume and material costs of the APS. However, with compactness the resulting high parasitic capacitance from the transformer primary to secondary can cause high common mode noise, and therefore should be mitigated. In this work, such designs meant for low power transformers are investigated, evaluated and compared.

This paper addresses the fundamentals of a behavioral model for a half bridge, designed to accurately represent switching losses at behavioral simulation level. In particular, it extends the classification of transistor modeling and examines the concept of mixed switching as an encompassing term for incomplete zero voltage switching. Finally, the paper analyzes the resulting loss mechanisms associated with various switching behaviors in a half-bridge topology.

Auxiliary power supplies (APS) form an integral part of power electronic systems in which the associated consumers have to be appropriately supplied. In this context, a voltage regulator (VR) circuit has been designed as a part of an APS, supplied from the drain-source voltage across a power semiconductor within a Modular Multilevel Converter (MMC) submodule (SM) [1], in order to achieve a high voltage (HV) DC output. In the hardware realization presented previously in [2], the duty cycle of the switching voltage was nearly 50 %. By extension of the same operating principle, an investigation is carried out in this work for operation with unequal on- and off-periods of the input AC voltage, at different operating points of the circuit over a wider range of the input RC time constants and varying duty ratios. Relevant calculations and simulations have been verified in hardware for a maximum output power of 50 W at 500 V DC, and presented in this paper.

This paper presents the prototyping of a fault-tolerant three-level T-type Neutral Point Clamped (TNPC) inverter for electric aircraft propulsion systems. To enhance robustness against various semiconductor failures, disconnecting devices are integrated in series with both the high-side and low-side switches. However, this implementation also increases parasitic inductance in the commutation loop. To mitigate the challenges associated with a highly inductive commutation path, a DC snubber circuit is designed to suppress overvoltage and damp switching oscillations. The switching behavior is analyzed through double-pulse testing (DPT). Additionally, a three-phase, three-level inverter employing space vector pulse-width modulation (SVPWM) is implemented, and its performance under normal operating conditions is evaluated. Furthermore, post-fault operation is investigated when one phase is connected to the neutral point.