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.

Implementation of a Transformerless Common-Mode Active Filter for Offline Converter Systems

Abstract: This paper presents a study and practical implementation of an active filter employing a high-frequency (HF) power amplifier and passive-filter components to be connected to the ac power lines in order to mitigate common-mode conducted emissions of three-phase pulsewidth modulation converter systems. The filter topology is chosen from different possibilities listed in a literature survey and studied regarding practical implementation issues, where requirements for an HF power amplifier to be applied in active filtering are derived. Special attention is put on the stability analysis where the challenges for the feedback are discussed, and a simple feedback structure is proposed. Other feedback concepts are analyzed, and limitations posed by stability requirements are presented. A prototype is designed and built, from which mathematical and experimental results are obtained demonstrating the potential and limitations of such a system.

Novel Three-Phase AC-DC-AC Sparse Matrix Converter Part I: Derivation, Basic Principle of Operation, Space Vector Modulation, Dimensioning

Abstract: A novel three-phase AC-DC-AC Sparse Matrix Converter (SMC) having no energy storage elements in the DC link and employing only 15 IGBTs as opposed to 18 IGBTs of a functionally equivalent conventional AC-AC matrix converter (CMC) is pro- posed. It is shown that the realization effort could be further reduced to only 9 IGBTs (Ultra Sparse Matrix Converter, USMC) in case the phase displacement of the fundamentals of voltage and current at the input and at the output is limited to ±π/6. The dependency of the voltage and current transfer ratios of the systems on the operating parameters is analyzed and a space vector modulation scheme is described in combination with a zero current commutation proce- dure. Furthermore, a safe multi-step current commutation concept is treated briefly. Conduction and switching losses of the SMC and USMC are calculated in analytically closed form. Finally, the theoretical results are verified in Part II of the paper by digital simulations and results of a first experimental investigation of a 10kW/400V SMC prototype are given.

A Three-Phase Delta Switch Rectifier for Use in Modern Aircraft

Abstract: In the course of the More Electric Aircraft program frequently active three-phase rectifiers in the power range of several kilowatts are required. It is shown that the three-phase -switch rectifier (comprising three -connected bidirectional switches) is well suited for this application. The system is analyzed using space vector calculus and a novel PWM current controller modulation concept is presented, where all three phases are controlled simultaneously; the analysis shows that the proposed concept yields optimal switching sequences. Analytical relationships for calculating the power components average and rms current ratings are derived to facilitate the rectifier design. A laboratory prototype with an output power of 5 kW is built and measurements taken from this prototype confirm the operation of the proposed current controller. Finally, initial EMI-measurements of the system are also presented.

Novel Tracking Power Supply for Linear Power Amplifiers

Abstract: Conventional linear power amplifiers (LPAs) 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 LPAs, e.g., for the realization of high power testing voltage sources. In this paper, a high-frequency isolated boost-type tracking power supply (TPS) system is proposed for the conditioning of the input voltage of an LPA. The output voltage of the TPS is varied according to the voltage to be formed by the LPA so that the voltage drop across the power amplifier output transistors is reduced to low values. This results in a significant increase of the total system efficiency. The operating principle of the proposed system is described. A design method for the output filter using the power supply rejection ratio of the LPA is proposed. This method ensures that the amplifier output voltage has minimal switching frequency components. Furthermore, a control system design method is presented that ensures good performance in the control of the constant inductor current of the switch-mode tracking stage. Finally, the theoretical considerations are verified by measurements on a 1-kW laboratory prototype.

Current Control of Three-Phase Rectifier Systems Using Three Independent Current Controllers

Abstract: Three-phase rectifier systems without connection of the neutral wire are characterized by the coupling of the phase input currents. Considering these couplings requires a transformation of the system equations into a static αβ-frame or into the rotating dq-reference frame where instead of the three coupled phase currents two independent current components are controlled. In this paper, it is shown that, despite of the existing cross-couplings, three independent phase current controllers can be used to control the system. Thereto, the cross coupling elements of the system transfer matrix have to fulfill some requirements which are derived using the Gershgorin theorem. The three-phase Δ-switch rectifier circuit is used for analysis and a detailed model of the rectifier system is derived where the cross couplings are visible. The model is subsequently used to evaluate the cross couplings and three independent current controllers are designed. Simulation and experimental results verify the control approach using three independent current controller for three-phase rectifier systems.

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.