Hans Ertl

Bio: Hans Ertl is an academic researcher from Vienna University of Technology. The author has contributed to research in topics: Three-phase & Rectifier. The author has an hindex of 20, co-authored 53 publications receiving 2547 citations. Previous affiliations of Hans Ertl include University of Vienna.

A passive three-phase rectifier enhanced by a DC-side high switching frequency add-on SiC-converter stage for unity power factor applications

Abstract: Recent developments showed that existing passive three-phase rectifier circuits with DC-side located smoothing inductor can be extended to a low harmonic input stage by adding an additional converter stage on the DC-side of the passive rectifier system. In this paper an implementation of this converter stage using reduced number of semiconductors (only two half-bridges) is proposed. The system shows input current distortions which can be reduced considerably to values below 1% if switching frequencies of 72kHz or above are used. A proper design of the injection chokes is thereto required and several operating modes and optimization possibilities are discussed. Design guidelines are verified by simulation results and a laboratory prototype based on a 10kW/72kHz rectifier system using SiC-MOSFETs.

Hybrid filter for a multi-cell switch-mode power amplifier

Abstract: The paper presents a novel filtering concept for multi-cell switch-mode power amplifiers intended to be used for high quality power sources up to the kW-region. Multi-cell switch-mode amplifiers usually are operated in interleaved PWM resulting in effective output voltage harmonics being much higher than the cell's switching frequency. This major advantage, however, is only given for ideally balanced DC-link voltages; actual systems typically will show low-frequency output voltage noise. For compensating this drawback, hence a closed loop hybrid output voltage filter concept is proposed formed by a combination of a switch-mode power and a linear-mode correction amplifier. The linear amplifier only has to deliver a few percent of the output power, compensating the switch-mode stages output voltage ripple, whereas the switch-mode system delivers nearly the whole output power. An interesting advantage of this system is that the linear amplifier can be designed concerning a comparatively low supply voltage as well as for low output current compared to the total system.

Implementation of a GaN Motor Inverter with an Observer-based Active Damped LC Filter

Abstract: In this paper, the implementation of a wide-bandgap (WBG) three phase motor inverter with integrated sinusoidal output voltage LC filter is analyzed. To ensure a well damped system behaviour at low losses, an active damping scheme based on filter capacitor current feedback is used, avoiding however any sensing of filter voltages/currents. The method is based on a linear observer model, which estimates the required filter capacitor currents for implementing the active damping. The paper gives an overview on the operating principle and reports the advantages in comparison to a standard IGBT inverter topology, caused by the obtained sinusoidal-shape output voltages. This results in an improved overall system efficiency, despite the fact, that the acoustic noise is reduced substantially and furthermore, the inverter-to-motor wiring is simplified by avoiding shielded cables.

Reliability of Capacitors for DC-Link Applications in Power Electronic Converters—An Overview

Abstract: DC-link capacitors are an important part in the majority of power electronic converters which contribute to cost, size and failure rate on a considerable scale. From capacitor users' viewpoint, this paper presents a review on the improvement of reliability of dc link in power electronic converters from two aspects: 1) reliability-oriented dc-link design solutions; 2) conditioning monitoring of dc-link capacitors during operation. Failure mechanisms, failure modes and lifetime models of capacitors suitable for the applications are also discussed as a basis to understand the physics-of-failure. This review serves to provide a clear picture of the state-of-the-art research in this area and to identify the corresponding challenges and future research directions for capacitors and their dc-link applications.

Control of a Single-Phase Cascaded H-Bridge Multilevel Inverter for Grid-Connected Photovoltaic Systems

Abstract: This paper presents a single-phase cascaded H-bridge converter for a grid-connected photovoltaic (PV) application The multilevel topology consists of several H-bridge cells connected in series, each one connected to a string of PV modules The adopted control scheme permits the independent control of each dc-link voltage, enabling, in this way, the tracking of the maximum power point for each string of PV panels Additionally, low-ripple sinusoidal-current waveforms are generated with almost unity power factor The topology offers other advantages such as the operation at lower switching frequency or lower current ripple compared to standard two-level topologies Simulation and experimental results are presented for different operating conditions

The Essence of Three-Phase PFC Rectifier Systems—Part II

Abstract: In the first part of this paper, three-phase power factor correction (PFC) rectifier topologies with sinusoidal input currents and controlled output voltage are derived from known single-phase PFC rectifier systems and/or passive three-phase diode rectifiers. The systems are classified into hybrid and fully active pulsewidth modulation boost-type or buck-type rectifiers, and their functionality and basic control concepts are briefly described. This facilitates the understanding of the operating principle of three-phase PFC rectifiers starting from single-phase systems, and organizes and completes the knowledge base with a new hybrid three-phase buck-type PFC rectifier topology denominated as Swiss Rectifier. Finally, core topics of future research on three-phase PFC rectifier systems are discussed, such as the analysis of novel hybrid buck-type PFC rectifier topologies, the direct input current control of buck-type systems, and the multi-objective optimization of PFC rectifier systems. The second part of this paper is dedicated to a comparative evaluation of four rectifier systems offering a high potential for industrial applications based on simple and demonstrative performance metrics concerning the semiconductor stresses, the loading and volume of the main passive components, the differential mode and common mode electromagnetic interference noise level, and ultimately the achievable converter efficiency and power density. The results are substantiated with selected examples of hardware prototypes that are optimized for efficiency and/or power density.

Multilevel Inverter Topologies for Stand-Alone PV Systems

Abstract: This paper shows that versatile stand-alone photovoltaic (PV) systems still demand on at least one battery inverter with improved characteristics of robustness and efficiency, which can be achieved using multilevel topologies. A compilation of the most common topologies of multilevel converters is presented, and it shows which ones are best suitable to implement inverters for stand-alone applications in the range of a few kilowatts. As an example, a prototype of 3 kVA was implemented, and peak efficiency of 96.0% was achieved.