다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

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.

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

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

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

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.

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

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.

Multilevel Inverter Topologies for Stand-Alone PV Systems

In order to reduce input current distortions and improve power factor of a passive three-phase diode bridge rectifier, an active add-on-option circuitry (”Flying Converter Cell”) has been introduced recently. A novel voltage balancing concept for such an active three-phase rectifier which is based on the third harmonic injection principle using a Flying Converter Cell (FCC) is proposed in this paper. It is shown that the midpoint voltage of the FCC can advantageously be used for balancing of the DC capacitor voltages without disturbing the input currents. The proposed balancing concept can simply be added to the existing controller structure consisting of current controllers and a voltage controller. Using the proposed active balancing any losses of alternative passive balancing concepts (resistor networks) can be avoided which maximizes the system’s efficiency. The proposed concept is described in a simple mathematical manner, limitations of the concept are derived and basic operation is verified by simulation results. Measurement results taken from a laboratory prototype with an output power of 10 kW finally demonstrate the good balancing characteristic of the proposed concept.

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DC Voltage Balancing of Flying Converter Cell Active Rectifier

A passive three-phase rectifier circuit equipped with a “Flying Converter Cell” (FCC) active current shaping network, based on the third harmonic injection concept, has been introduced recently. This additional/optional circuit allows the upgrade of a standard B6 diode rectifier to a low harmonic input stage with unity power factor. In order to guarantee properly shaped sinusoidal mains input currents, dedicated current and voltage controllers of the active circuitry must be designed carefully. As the active current injection unit consists of an assembly of three individual converter stages, the design procedure of both current and superimposed voltage controllers results in fairly high complexity. It is, therefore, going to be discussed in detail in this work. Based on the analysis of the rectifier system, an appropriate control concept is developed which is implemented using a digital signal processor. It is furthermore shown that the midpoint voltage of the FCC can advantageously be used for balancing of the dc capacitor stage of the cell without deteriorating total harmonic distortion of mains input currents. Measurement results taken from a 10 kW/10 kHz laboratory prototype finally confirm promising characteristics of the total hybrid system.

Control Concepts for Hybrid Rectifiers Utilizing a Flying Converter Cell Active Current Injection Unit

Multitudinous industry applications require single-phase or three-phase rectification circuits. Hybrid rectifiers offer fairly flexible fields of applications (compared to purely implemented passive or active rectifiers) due to their optional active converter topology. The low harmonic input stage, however, is in general exposed to unbalanced AC-side mains voltage conditions. Depending on location and/or facility, input voltage variations can be 3% or higher (short-term). Imbalance in mains input voltages on hybrid rectifiers which are employing the third harmonic injection principle are therefore analysed in detail. It is shown that unbalanced AC-side input voltages not only directly influence THD of input currents and power factor of the system, but also increase current stress of active switches and passive components. Basic considerations are discussed from a mathematical point of view and are finally confirmed by simulation and experimental results of a 10 kW/10 kHz laboratory prototype (passive three-phase diode bridge rectifier equipped with ‘Flying’ Converter Cell (FCC) active current injection cell).

Effects of unbalanced mains voltage conditions on three-phase hybrid rectifiers employing third harmonic injection

Modern grid connected power electronics (PE) technology more and more relies on both, high sophisticated testing and validation equipment and methods in order to pre-address severe impact of specific PE solutions on the local grid before going online. The most efficient and promising testing environment in terms of power density, results in an implemented switched-mode power amplifier which is capable of emulating output impedances like RL-components over a wide frequency range instead of coming up with real bulky passive components. Such AC power source technology has been introduced recently. The main objective of such specific test equipment is the integration of a proper control scheme for applied virtual grid impedance emulation. Thus, an AC-sweep analysis, regarding a performed offline simulation supported by experimental results might become handy in order to proof validity of the proposed concept. Hence, this paper is focused on an at least 2 kHz bandwidth AC-simulator hardware and software characterization, based on a comparison between a prepared offline simulation (PLECs), hardware-in-the-loop simulation (C-HIL, Typhoon HIL) and measurement results of an implemented 3 kW/200 kHz laboratory prototype.

AC-Sweep Analysis and Verification of an AC Power Source with Virtual Output Impedance for Validation of Grid Connected Components

In a converter 1 for a d.c. voltage consumer 2 supplied via a single or multi-phase a.c. voltage source 3, between the a.c. voltage source 3 and the d.c. voltage consumer 2 is arranged a rectifier 5 and an intermediate circuit 6 for controlling the voltage in the d.c. voltage consumer 2. The intermediate circuit 6 is associated with a control device 29. The control device 29 is connected at the input of the d.c. voltage consumer 2 with external voltage and/or current adjusting or monitoring devices. The output of the control device 29 is applied to a control input of a switching device 24. The switching device 24 is arranged between an electric energy store 26 and a magnetic energy store 19 and the intermediate circuit 6 is provided between the energy storage element 26 and the magnetic energy store 19. The switching device 24 may be a bipolar transistor (46, Fig 5), two devices (24, 56 Fig 6), GTO thyristors (97-99, Figs 12 and 16), IGBT (Figs 13, 14, 17 and 20). The d.c. voltage consumer 2 may be used for welding 33, 34.

Hans Ertl

Papers

DC Voltage Balancing of Flying Converter Cell Active Rectifier

Control Concepts for Hybrid Rectifiers Utilizing a Flying Converter Cell Active Current Injection Unit

Effects of unbalanced mains voltage conditions on three-phase hybrid rectifiers employing third harmonic injection

AC-Sweep Analysis and Verification of an AC Power Source with Virtual Output Impedance for Validation of Grid Connected Components

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