Abstract-Multilevel inverter technology has emerged recently as a very important alternative in the area of high-power medium-voltage energy control. This paper presents the most important topologies like diode-clamped inverter (neutral-point clamped), capacitor-clamped (flying capacitor), and cascaded multicell with separate dc sources. Emerging topologies like asymmetric hybrid cells and soft-switched multilevel inverters are also discussed. This paper also presents the most relevant control and modulation methods developed for this family of converters: multilevel sinusoidal pulsewidth modulation, multilevel selective harmonic elimination, and space-vector modulation. Special attention is dedicated to the latest and more relevant applications of these converters such as laminators, conveyor belts, and unified power-flow controllers. The need of an active front end at the input side for those inverters supplying regenerative loads is also discussed, and the circuit topology options are also presented. Finally, the peripherally developing areas such as high-voltage high-power devices and optical sensors and other opportunities for future development are addressed.
This paper presents an impedance-source (or impedance-fed) power converter (abbreviated as Z-source converter) and its control method for implementing dc-to-ac, acto-dc, ac-to-ac, and dc-to-dc power conversion. The Z-source converter employs a unique impedance network (or circuit) to couple the converter main circuit to the power source, thus providing unique features that cannot be obtained in the traditional voltage-source (or voltage-fed) and current-source (or current-fed) converters where a capacitor and inductor are used respectively. The Z-source converter overcomes the conceptual and theoretical barriers and limitations of the traditional voltage-source converter (abbreviated as V-source converter) and current-source converter (abbreviated as Isource converter) and provides a novel power conversion concept. The Z-source concept can be applied to all dc-to-ac, acto-dc, ac-to-ac, and dc-to-dc power conversion. To describe the operating principle and control, this paper focuses on an example: a Z-source inverter for dc-ac power conversion needed in fuel cell applications. Simulation and experimental results will be presented to demonstrate the new features.
In this paper, theoretical results are shown for several novel inverters. These inverters are similar to the ZSource inverters presented in previous works, but have several advantages, including in some combination; lower component ratings, reduced source stress, reduced component count and simplified control strategies. Like the Z-Source inverter, these inverters are particularly suited for applications which require a large range of gain, such as in motor controllers or renewable energy. Simulation and experimental results are shown for one topology to verify the analysis. Also, a back-to-back inverter system featuring bidirectionality on both inverters, as well as secondary energy storage with only a single additional switch, is shown.
This paper presents transformerless multilevel converters as an application for high-power and/or high-voltage electric motor drives. Multilevel converters: 1) can generate nearsinusoidal voltages with only fundamental frequency switching; 2) have almost no electromagnetic interference or common-mode voltage; and 3) are suitable for large voltampere-rated motor drives and high voltages. The cascade inverter is a natural fit for large automotive all-electric drives because it uses several levels of dc voltage sources, which would be available from batteries or fuel cells. The back-to-back diode-clamped converter is ideal where a source of ac voltage is available, such as in a hybrid electric vehicle. Simulation and experimental results show the superiority of these two converters over two-level pulsewidthmodulation-based drives. Index Terms-Cascade inverter, common-mode voltage, diodeclamped inverter, electric vehicle, motor drive, multilevel converter, multilevel inverter.
A DC -DC converter topology is proposed. The DC -DC multilevel boost converter (MBC) is a pulse-width modulation (PWM)-based DC -DC converter, which combines the boost converter and the switched capacitor function to provide different output voltages and a self-balanced voltage using only one driven switch, one inductor, 2N 2 1 diodes and 2N 2 1 capacitors for an Nx MBC. It is proposed to be used as DC link in applications where several controlled voltage levels are required with self-balancing and unidirectional current flow, such as photovoltaic (PV) or fuel cell generation systems with multilevel inverters; each device blocks only one voltage level, achieving high-voltage converters with low-voltage devices. The major advantages of this topology are: a continuous input current, a large conversion ratio without extreme duty cycle and without transformer, which allow high switching frequency. It can be built in a modular way and more levels can be added without modifying the main circuit. The proposed converter is simulated and prototyped; experimental results prove the proposition's principle.
This paper extends the impedance-source (Z-source) inverters concept to the transformer-based Z-source (trans-Zsource) inverters. The original Z-source inverter (ZSI) employs an impedance network of two inductors and two capacitors connected in a special arrangement to interface the dc source and the inverter bridge. It has buck and boost function that cannot be achieved by traditional voltage-source inverters and currentsource inverters. In the proposed four trans-Z-source inverters, all the impedance networks consist of a transformer and one capacitor. While maintaining the main features of the previously presented Z-source network, the new networks exhibit some unique advantages, such as the increased voltage gain and reduced voltage stress in the voltage-fed trans-ZSIs and the expanded motoring operation range in the current-fed trans-ZSIs, when the turns ratio of the transformer windings is over 1. Simulation and experimental results of the voltage-fed and the current-fed trans-ZSIs are provided to verify the analysis.Index Terms-Current-source inverter, dc-ac conversion, voltage-source inverter, Z-source inverter.
This paper presents an impedance-source (or impedance-fed) power converter (abbreviated as Z-source converter) and its control method for implementing dc-to-ac, ac-to-dc, ac-to-ac, and dc-to-dc power conversion. The Z-source converter employs a unique impedance network (or circuit) to couple the converter main circuit to the power source, thus providing unique features that cannot be obtained in the traditional voltage-source (or voltage-fed) and current-source (or current-fed) converters where a capacitor and inductor are used, respectively. The Z-source converter overcomes the conceptual and theoretical barriers and limitations of the traditional voltage-source converter (abbreviated as V-source converter) and current-source converter (abbreviated as I-source converter) and provides a novel power conversion concept. The Z-source concept can be applied to all dc-to-ac, ac-to-dc, ac-to-ac, and dc-to-dc power conversion. To describe the operating principle and control, this paper focuses on an example: a Z-source inverter for dc-ac power conversion needed in fuel cell applications. Simulation and experimental results will be presented to demonstrate the new features.Index Terms-Converter, current-source inverter, inverter, voltage-source inverter, Z-Source inverter.
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