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.

Novel Three-Phase CM/DM Conducted Emission Separator

Abstract: This paper presents two novel three-phase common-mode (CM)/differential-mode (DM) noise separation networks, which are passive and active networks, to be used in electromagnetic compatibility conducted emission (CE) measurements of three-phase equipment. The passive network is analyzed theoretically, and a prototype is constructed and tested. Its evaluation is presented through frequency response measurements and CE tests performed on a three-phase motor drive and verifies that the network is capable of separating the CM and DM information in a CE measurement condition.

Active voltage balancing of DC-link electrolytic capacitors

Abstract: DC voltage links of three-phase power converters are frequently equipped with a series connection of two electrolytic capacitors because of high voltage level. For such a configuration, usually resistors have to be arranged in parallel to each capacitor in order to balance the partial voltages. These balancing resistors, however, have to be dimensioned regarding the worst-case scenario of capacitor's leakage currents; such leakage can lead to high permanent dissipative losses that also appear in case of low actual leakage currents. To avoid these losses to a very large extent, a novel low-cost and robust active unit for replacing the passive balancing resistors is introduced. The paper describes the operating principle of the circuit, analyses the fundamental relationships relevant for the balancing characteristic and gives guidelines concerning component selection. Furthermore, simulation results as well as measurements taken from a laboratory prototype are presented.

On the Tradeoff Between Input Current Quality and Efficiency of High Switching Frequency PWM Rectifiers

Abstract: Due to their basic physical properties, power MOSFETs exhibit an output capacitance Coss that is dependent on the drain-source voltage. This (nonlinear) parasitic capacitance has to be charged at turn-off of the MOSFET by the drain-source current in rectifier applications that yield input current distortions. A detailed analysis shows that the nonlinear behavior of this capacitance is even more pronounced for modern super junction MOSFET devices. Whereas Coss increases with increasing chip area, the on-state resistance of the MOSFET decreases accordingly. Hence, a tradeoff between efficiency and input current distortions exists. A detailed analysis of this effect considering different semiconductor technologies is given in this study and a Pareto curve in the η-THDI space is drawn that clearly highlights this relationship. It is further shown that the distortions can be reduced considerably by the application of a proper feedforward control signal counter- acting the nonlinear switching delay due to Coss. The theoretical considerations are verified by experimental results taken from 10-kW laboratory prototypes with the switching frequencies of 250 kHz and 1 MHz.

How to include the dependency of the R/sub DS(on/) of power MOSFETs on the instantaneous value of the drain current into the calculation of the conduction losses of high-frequency three-phase PWM inverters

Abstract: In this paper, the conduction losses of power MOSFETs are calculated analytically for application in three-phase voltage DC-link pulsewidth modulation (PWM) power converter systems. Contrary to a conventional calculation, the dependency of the turn-on behavior on the drain current is considered in terms of a quadratic approximation. The derived relationships are represented graphically; they can be included directly into the dimensioning of the power transistors.

EMI filter design for high switching frequency three-phase/level PWM rectifier systems

Abstract: The actual attenuation characteristic of EMI filters in practice often differs from theoretical predictions and minor changes could result in a significant performance improvement. Whereas the performance of the differential-mode (DM) filter stage usually can be well predicted, the common-mode (CM) behavior is more difficult to handle. This is especially true for three-phase PWM rectifier systems, which show a large high-frequency CM voltage at the rectifier output. In this work the possible CM noise current paths of a three-phase/level PWM rectifier are analyzed where parasitic capacitances to the heat sink and to earth are considered. Additionally, a concept to significantly reduce CM emissions is discussed in detail. Based on the proposed models an EMI filter design for a system with 1 MHz switching frequency is shown. Experimental verification of the designed EMI filter is presented by impedance and conducted emission (CE) measurements taken from a 10 kW hardware prototype. Several practical aspects of filter realization like component arrangement, shielding layers, magnetic coupling etc. are discussed and verified by measurements.

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.