Meissner, Michael

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.

The novel modular multilevel converter (MMC) topology, named Double Zero Submodule in Double Connection (DZDCSM) [1], capable of generating four levels of terminal voltage, is one of the most suitable candidates for MMC applications in the future. During operation of these MMC submodules (SM), isolated auxiliary voltages are needed to drive associated consumers like gate drivers, DC-DC converters, controllers etc. They can be generated from the available high DC-link voltage during operation of the SM, and used to charge a battery bank, which can meet the auxiliary load demand, in addition to precharging the SM capacitors. The objective of this research is to obtain such an isolated auxiliary low DC voltage to power a typical Li-ion battery charger. For this, it is proposed in this work to energize the corresponding battery charging circuit by utilizing transients in the drain-source voltage appearing across one SM power semiconductor. In this paper, such a charging circuit is investigated to achieve an isolated 5 V (DC) from 1.5 kV (AC) over two stages of voltage step down, and a hardware realization as proof-of-concept is presented. The power converter consisting of several SMs is designed to generate 20 MW. Therefore, during its operation, achieving a high efficiency of the investigated battery charging circuit delivering only a few tens of watts per SM is not important. Calculations of a simplified equivalent circuit are performed, verified by simulation, and implemented in hardware.

In this paper an orthogonal field coupled current controlled adjustable inductance is integrated into standard topology, namely a buck converter. By adjusting the inductance the ripple current, directly dependent on this, shall be changed as a proof of concept. In addition, potential risks of the adjustable inductance are examined, coming from magnetic back coupling from load into control circuit.

In this paper the investigation of a modified version of the non-isolated cascaded buck-boost converter is presented in order to achieve a better voltage balancing of the converter with respect to ground. This should reduce common mode noise due to the parasitic capacitive coupling between the switching nodes, heat sinks and protective earth. Measurements confirm the balancing capabilities of the described symmetry circuit, leading to significantly reduced common mode noise.

This work presents a feasibility study of power supply solutions for isolated gate drivers meant for use in high voltage applications. At high potential differences, maintaining the standard specified creepage and clearances increases the size and volume of the integrated system. Therefore, this becomes a bottleneck in space-constrained applications. In this work, the galvanically isolated power supply for gate drivers designed to drive a modular multilevel converter [1] is realized by using a common primary voltage source to supply multiple gate driver units over individual isolation transformers. Two configurations of isolation have been investigated, and two further power supply arrangements have been constructed and tested in nominal operation. All arrangements have their own advantages and disadvantages, and therefore, a preferred selection is dependent on application, and the available volume to integrate the solution. A comparison of the configurations in terms of their performances, robustness against partial discharges and the associated construction effort concludes this paper.

In this paper the realization of a concept for an adjustable inductance with different composites of magnetic core material is described, analyzed and discussed. An electrical circuit is used to generate a magnetic field by an additional control core which is orthogonal to the magnetic field of the load core and thereby change the inductance. It is shown that the system can be influenced in different ways by the chosen material mixtures.

In this publication the effect of the operating temperature on the effective inductance of a controllable inductor is analysed. The main difference compared to a coil with a simple single core lies in the current-controlled inductance-value. This is achieved by a second core implemented perpendicular upon the load-toroid affecting the saturation within a limited shared volume. Corresponding to the presented analysis, the dependencies on the core temperatures are investigated by measurements.

Advanced investigations on a previously published concept for an adjustable inductance are presented. The influence of the operating temperature will be analysed by measurement as an additional parameter for a current controlled inductor. Due to construction a defined area of the load core can be saturated to change the effective inductance. For the setup an additional core generating an orthogonal magnetic field is implemented perpendicular to a corresponding load core.

According to the recent trend, SiC-MOSFETs have been increasingly conquering the sector of high power semiconductors [1]. This also includes the field of discrete devices for high frequency high current applications which has been dominated by Si-IGBTs in the past and the present. Compared to these Si-IGBTs the wide band gap (WBG) devices can perform very fast switching with very high slew rates. In the proposed survey, state of the art discrete SiC-MOSFETs will be analysed in a high quality measurement setup in order to rate and compare the dynamic characteristics.