Felix A. Himmelstoss

Bio: Felix A. Himmelstoss is an academic researcher from University of Applied Sciences Technikum Wien. The author has contributed to research in topics: Ćuk converter & Boost converter. The author has an hindex of 10, co-authored 76 publications receiving 356 citations. Previous affiliations of Felix A. Himmelstoss include Vienna University of Technology & Applied Science Private University.

High Efficiency DC-to-AC Power Inverter with Special DC Interface

Abstract: In case of medium voltage (several tens up to hundred volts on DC-side) solar inverter applications, a DC-to-DC converter for voltage level adaptation is required in series of the DC-to-AC inverter. This leads to a two-stage concept with accumulation of the losses. In our case a concept was chosen where the efficiency of each stage is maximized by using the best topology. The given requirements make the application of a non-isolated design imperative to avoid additional transformer losses. In this paper a 60V–120V DC (input) to 230V AC (output) / 1kW converter with minimal conversion losses is derived. A simple modification in the inverter's output section leads to a significant improvement of the losses in the inverter system. Only three additional components (two diodes and one inductor) are necessary to optimize the inverter's power stage. The topology presented here shows a remarkable improvement of the switching losses and significantly reduced EMC. It is well-suited for solar power inverter applications.

Low-loss converters with high step-up conversion ratio working at the border between continuous and discontinuous mode

Abstract: The use of tapped inductors in the classical boost or buck-boost converter leads to a high step-up ratio thus avoiding the extreme duty cycles of the active switch and the high peak currents in the active and passive switches. Two converters are presented and analyzed. Due to the simultaneous regulation of the switching frequency and the duty cycle on one hand and the winding ratio of an autotransformer on the other, high conversion rates of 1:5 can easily be realized. The dimensioning of the converters, their dynamical behavior, and the component stresses are analyzed.

High dynamic class-D power amplifier

Abstract: Class-D amplifiers have high efficiency and are used when high audio frequency power is necessary and also when low power consumption in battery powered equipment is required. A new kind of class-D amplifier is presented and analyzed. The ripple of the high power class-D amplifier stage is compensated by a small (low power) high dynamic amplifier, which can be realized either as an analog one or as a second power class-D converter. The main part of the power is handled by a half-bridge with relatively small switching frequency (compared to the output bandwidth) and therefore low switching losses. Furthermore, the compensation mechanism leads to no additional current or voltage stress in the main switching stage. In the presented example the switching frequency of the main power processor is selected at only twice the required output bandwidth of the amplifier. The resulting output ripple is compensated by using the transformer coupled supplement power processor. Only small filters are necessary. The concept is well suited for consumer as well as aerospace applications as due to the improved efficiency, and the battery lifetime can be increased without any quality reduction.

Bidirectional DC-to-DC converter for solar battery backup applications

Abstract: The application of battery backup systems automatically leads to inverter structures with relative low input voltage levels compared to the DC-link voltage. To guarantee the required system capability the power electronic system has to maintain the resulting high input current ratings. This leads to a problematic design with noticeable efficiency restrictions. To improve the overall efficiency of the inverter and to reduce the input capacitor, a possible solution is the parallel operation of several converter stages. Here, a special disadvantage has to be marked: The parallel operation of conventional DC-to-DC converters with voltage source characteristics mostly used requires special control mechanism to ensure correct power distribution. Contrary to this behavior, current sourced converter types can act in parallel without any special measurements. The solution proposed in this paper is capable to improve the parallel operation of power stages in conventional converters with modern current sharing techniques. Due to the reduced current in each of the paralleled output stages, the efficiency will increase significantly. The ripple of the input current is shared between the different stages, which helps to reduce the input capacitor in each string. In addition, the resulting frequency rises with the number of used stages when multiphase operation is used. This leads to a more silent (EMC) design. Another big problem, the output rectifier operating at the high DC-link voltage, can be disburdened significantly by using the suggested current sourced inverter structure. In this paper a bidirectional 12V / 500 W current sourced inverter for solar battery applications is described. Due to the special design, it could be built up by the usage of cheap mass components. The power stage operates at 50 kHz, supplying a 400 V DC-link.

Analysis of a boost converter with tapped inductor and reduced voltage stress across the buffer capacitor

Abstract: A step-up converter with tapped inductor is analyzed. Compared to the classical boost converter, the structure has been slightly modified which offers the advantage of reduced voltage stress across the buffer capacitor and due to a transformer the voltage transformation rate is changed. The classical and most common converter uses a simple inductor, leading to the disadvantage of extreme duty ratios when high voltage transfer ratios are needed. To meet such requirements, a tapped inductor (autotransformer) can be used instead of the ordinary inductor thus avoiding excessive duty ratios. After basic analyses in the continuous inductor current mode, important data for the dimensioning of the components, like the voltage and the current stress, and the equations for the component values are given. Moreover, a state space model and linearized transfer functions for the control of the converter are derived. When transformed into a bidirectional converter, it can be used for coupling two voltage links and as a two quadrant chopper for DC motors. To verify the proper function of this modified boost topology, a small test converter has been designed. Measurement results and a more precise model are given in the appendix.

Review of Nonisolated High-Step-Up DC/DC Converters in Photovoltaic Grid-Connected Applications

Abstract: The photovoltaic (PV) grid-connected power system in the residential applications is becoming a fast growing segment in the PV market due to the shortage of the fossil fuel energy and the great environmental pollution. A new research trend in the residential generation system is to employ the PV parallel-connected configuration rather than the series-connected configuration to satisfy the safety requirements and to make full use of the PV generated power. How to achieve high-step-up, low-cost, and high-efficiency dc/dc conversion is the major consideration due to the low PV output voltage with the parallel-connected structure. The limitations of the conventional boost converters in these applications are analyzed. Then, most of the topologies with high-step-up, low-cost, and high-efficiency performance are covered and classified into several categories. The advantages and disadvantages of these converters are discussed. Furthermore, a general conceptual circuit for high-step-up, low-cost, and high-efficiency dc/dc conversion is proposed to derive the next-generation topologies for the PV grid-connected power system. Finally, the major challenges of high-step-up, low-cost, and high-efficiency dc/dc converters are summarized. This paper would like to make a clear picture on the general law and framework for the next-generation nonisolated high-step-up dc/dc converters.

Power Electronics Converters Applications And Design

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Survey on non-isolated high-voltage step-up dc–dc topologies based on the boost converter

Abstract: The major consideration in dc-dc conversion is often associated with high efficiency, reduced stresses involving semiconductors, low cost, simplicity and robustness of the involved topologies. In the last few years, high-step-up non-isolated dc-dc converters have become quite popular because of its wide applicability, especially considering that dc-ac converters must be typically supplied with high dc voltages. The conventional non-isolated boost converter is the most popular topology for this purpose, although the conversion efficiency is limited at high duty cycle values. In order to overcome such limitation and improve the conversion ratio, derived topologies can be found in numerous publications as possible solutions for the aforementioned applications. Within this context, this work intends to classify and review some of the most important non-isolated boost-based dc-dc converters. While many structures exist, they can be basically classified as converters with and without wide conversion ratio. Some of the main advantages and drawbacks regarding the existing approaches are also discussed. Finally, a proper comparison is established among the most significant converters regarding the voltage stress across the semiconductor elements, number of components and static gain.