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.

Comparative evaluation of multi-loop control schemes for a high-bandwidth AC power source with a two-stage LC output filter

Abstract: This paper presents a comparative evaluation of four different multi-loop control schemes for a high-bandwidth AC power source. The power source considered in this work is based on a three-level T-type inverter with a two-stage LC output filter. The control schemes evaluated in this paper have an output voltage controller in the outer loop. For the inner control loop the following options are evaluated: capacitor current feedbacks, proportional-integral and proportional inverter output current control in combination with reference voltage and load current feedforward, and first LC stage capacitor voltage and inverter output current feedback.

Design of a 100 kHz wide bandgap inverter for motor applications with active damped sine wave filter

Abstract: In this study, a three-phase motor inverter with sinusoidal output voltages based on the application of gallium nitride transistors and advanced control is analysed. In comparison to standard silicon-insulated gate bipolar transistors much higher feasible switching frequencies of 100 kHz and above are possible and reduce the output sine filter component size such that the filter can be directly included into the inverter. This considerably improves the electromagnetic interference (EMI) behaviour of the drive system as well as the acoustic noise, eases the inverter-to-motor wiring and protects the motor isolation against high d u /d t rates. The study describes the dimensioning and design of the used two-stage LC filter including motor current control based on proportional-integral-type phase current controllers. The LC filter damping is performed actively by capacitor current feedback. Using this active damping scheme avoids additional losses of conventional sine filters and guarantees high system efficiency up to 98%. Finally, experimental results of a laboratory prototype verify the proper behaviour of the proposed concept.

Implementation of a transformer-less common mode active filter for off-line converter systems

Abstract: This work presents a study and practical implementation of an active filter employing a HF power amplifier and passive filter components to be connected to the AC power lines in order to mitigate common mode conducted emissions of PWM converter systems. The filter topology is chosen from different possibilities listed in a literature survey and studied regarding practical implementation issues. Special attention is put on the stability analysis where the challenges for the feedback structure are discussed and a simple feedback structure is proposed. A prototype is designed and built, from which mathematical and experimental results are obtained demonstrating the potential and limitations of such a system.

Wideband Current Transducer for Measuring AC Signals With Limited DC Offset

Abstract: In many applications, a current measurement that can measure AC currents with DC offset is required. This is not possible using conventional current transformers (CTs) due to the core saturation because of the DC offset. In this paper, a new sensor concept is presented, which consists of a wideband CT and a demagnetizing circuit. The sensor concept is capable of measuring AC currents with DC offset, which have periodic zero crossings, as given in power-factor-corrected (PFC) circuits. Using the demagnetization circuit, the core is actively reset during the zero crossing intervals. The operation principle and design equations are discussed in detail in this paper. For validating the presented concept, three sensors have been built using different core materials, and measurements of the transfer functions as well as operation in a PFC system are presented. A bandwidth from DC up to 20 MHz has been achieved.

Basic considerations and topologies of switched-mode assisted linear power amplifiers

Abstract: The paper presents a combined power amplifier system consisting of a linear amplifier unit with a switched-mode (class D) current dumping stage arranged in parallel. With this topology, the fundamental drawback of conventional linear power amplifiers-the high loss-is avoided. Compared to a pure class D (switching) amplifier, the presented system needs no output filter to reduce the switching frequency harmonics. This filter (usually of multi-stage type) generally deteriorates the transient response of the system and impairs the feedback loop design. Furthermore, the low-frequency distortions of switching amplifiers caused by the interlock delay of their power transistors are avoided with the presented switched-mode assisted linear amplifier system. This can be considered as a master-slave system with a guiding linear amplifier and a supporting class D slave unit. The paper describes the operating principle of the system, analyzes the fundamental relationships for the circuit design and presents simulation results. Finally, various further topologies of switched-mode assisted linear amplifiers are given.

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.