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.

Basic linear-mode solar-cell simulators

Abstract: The paper describes basic types of linear-mode power systems for simulating voltage/current characteristics of solar cells modules Starting from a current source with a chain of diodes arranged in parallel (being the most simple equivalent circuit diagram of a solar power module) a very basic solar module simulator using a bipolar power transistor and based on the “amplified diode” concept is developed Furthermore, this principle is modified utilizing a linear-mode series regulator in order to reduce the dissipated power at no-load condition The paper includes a detailed description of the different operating principles, gives dimensioning guidelines and presents also measurement results taken from laboratory prototype systems

High-frequency isolated DC/DC converter for input voltage conditioning of a linear power amplifier

Abstract: Conventional linear power amplifiers show a high output voltage quality but are characterized by high power losses and/or low power density. Therefore, there is a growing interest in increasing the efficiency of linear power amplifiers, e.g. for the realization of high power testing voltage sources. In this paper a high-frequency isolated DC/DC converter system for the conditioning of the input voltage of a linear power amplifier. The output voltage of the DC/DC converter is varied according to the output voltage to be formed by the linear power amplifier so that the voltage drop occurring across the power amplifier output transistors is reduced to low values which results in a significant increase of the total system efficiency. The control design of the DC/DC converter is for fast output voltage response according to the high large signal bandwidth of the linear power amplifier. The three-level input stage of the proposed system does allow a direct connection to the output of a three-phase three-level PWM rectifier ensuring low effects on the supplying mains. The operating principle of the proposed system is described and the design of the output voltage control is treated in detail. The resulting dynamic behavior of the system is analyzed by digital simulation. Finally, the theoretical considerations are verified by measurements on a 1.5 kW laboratory prototype.

Dimensioning and Control of a Switch-Mode Power Amplifier Employing a Capacitive Coupled Linear-Mode Ripple Suppression Stage

Abstract: A new power amplifier system focused mainly on EMC testing applications is analyzed. The proposed topology consists of a three-level switching power amplifier connected in parallel with a capacitive coupled linear stage which absorbs the output current ripple of the switch-mode stage resulting in an almost ripple-free output voltage of the total amplifier. This concept alternatively can also be interpreted as a switch-mode power amplifier with a hybrid output filter consisting of a passive LC-circuit and of a linear amplifier which compensates the voltage ripple appearing across the filter capacitor (resulting from the ripple current of the switch-mode stage). The design of the linear amplifier has to be performed only regarding the ripple voltage and the ripple current of the passive filter part. Consequently, the rated power of the amplifier and the appearing losses become low as compared to the output power of the total system. A further advantage of the concept is that the output impedance of the total system will be determined mainly by the linear stage. Therefore, contrary to conventional switch-mode amplifiers where the output filter significantly worsens the output impedance, the presented system concerning this property (which especially is important for EMC testing applications) almost is equivalent to a pure linear power amplifier which, however, would show a much lower efficiency. The paper describes the operating principle of the system, specifies the fundamental relationships being relevant to the circuit design and analyzes the control behavior of the switch-mode stage as well as of the linear circuit part.

Design and experimental verification of a third harmonic injection rectifier circuit using a Flying converter cell

Abstract: The proposed active three-phase rectifier circuit utilizing a Flying Converter Cell (FCC) based on the concept of third harmonic injection allows the extension of a passive three-phase diode bridge rectifier to a low-harmonic input stage (THDi <; 5%) for applications where dc-link voltage control is not required. In this work the design and experimental verification of a 10kW laboratory prototype using the proposed concept is addressed. Based on the analysis of the rectifier system a control concept is developed which is implemented in a digital signal processor. It is shown that the proposed rectifier system shows several degrees of freedom which can be used for system optimization. Several implementation details are discussed and experimental results taken from the constructed 10kW laboratory prototype demonstrate the good performance of the proposed rectifier system and verify the proper operation of the developed control concepts.

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.