9,224 research outputs found

    Multilevel Converters: An Enabling Technology for High-Power Applications

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    | Multilevel converters are considered today as the state-of-the-art power-conversion systems for high-power and power-quality demanding applications. This paper presents a tutorial on this technology, covering the operating principle and the different power circuit topologies, modulation methods, technical issues and industry applications. Special attention is given to established technology already found in industry with more in-depth and self-contained information, while recent advances and state-of-the-art contributions are addressed with useful references. This paper serves as an introduction to the subject for the not-familiarized reader, as well as an update or reference for academics and practicing engineers working in the field of industrial and power electronics.Ministerio de Ciencia y Tecnología DPI2001-3089Ministerio de Eduación y Ciencia d TEC2006-0386

    The Essential Role and the Continuous Evolution of Modulation Techniques for Voltage-Source Inverters in the Past, Present, and Future Power Electronics

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    The cost reduction of power-electronic devices, the increase in their reliability, efficiency, and power capability, and lower development times, together with more demanding application requirements, has driven the development of several new inverter topologies recently introduced in the industry, particularly medium-voltage converters. New more complex inverter topologies and new application fields come along with additional control challenges, such as voltage imbalances, power-quality issues, higher efficiency needs, and fault-tolerant operation, which necessarily requires the parallel development of modulation schemes. Therefore, recently, there have been significant advances in the field of modulation of dc/ac converters, which conceptually has been dominated during the last several decades almost exclusively by classic pulse-width modulation (PWM) methods. This paper aims to concentrate and discuss the latest developments on this exciting technology, to provide insight on where the state-of-the-art stands today, and analyze the trends and challenges driving its future

    Low Voltage Regulator Modules and Single Stage Front-end Converters

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    Evolution in microprocessor technology poses new challenges for supplying power to these devices. To meet demands for faster and more efficient data processing, modem microprocessors are being designed with lower voltage implementations. More devices will be packed on a single processor chip and the processors will operate at higher frequencies, exceeding 1GHz. New high-performance microprocessors may require from 40 to 80 watts of power for the CPU alone. Load current must be supplied with up to 30A/µs slew rate while keeping the output voltage within tight regulation and response time tolerances. Therefore, special power supplies and Voltage Regulator Modules (VRMs) are needed to provide lower voltage with higher current and fast response. In the part one (chapter 2,3,4) of this dissertation, several low-voltage high-current VRM technologies are proposed for future generation microprocessors and ICs. The developed VRMs with these new technologies have advantages over conventional ones in terms of efficiency, transient response and cost. In most cases, the VRMs draw currents from DC bus for which front-end converters are used as a DC source. As the use of AC/DC frond-end converters continues to increase, more distorted mains current is drawn from the line, resulting in lower power factor and high total harmonic distortion. As a branch of active Power factor correction (PFC) techniques, the single-stage technique receives particular attention because of its low cost implementation. Moreover, with continuously demands for even higher power density, switching mode power supply operating at high-frequency is required because at high switching frequency, the size and weight of circuit components can be remarkably reduced. To boost the switching frequency, the soft-switching technique was introduced to alleviate the switching losses. The part two (chapter 5,6) of the dissertation presents several topologies for this front-end application. The design considerations, simulation results and experimental verification are discussed

    Analysis of a new family of DC-DC converters with input-parallel output-series structure

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    There is an increasing trend of development and installation of switching power supplies due to their highly efficient power conversion, fast power control and high quality power conditioning for applications such as renewable energy integration and energy storage management systems. In most of these applications, high voltage conversion ratio is required. However, basic switching converters have limited voltage conversion ratio. There has been much research into development of high gain power converters. While most of the reported topologies focus on high gain and high efficiency, in this thesis, the input and output ripple currents and reliability are also considered to derive a new converter structure suitable for high step-up voltage conversion applications. High ripple currents and voltages at the input and output of dc-dc converters are not desirable because they may affect the operation of the dc source or the load. A number of converters operating in an interleaved manner can reduce these ripples. This thesis proposes a dc/dc switching converter structure which is capable of reducing the ripple problem through interleaved action, in addition to high gain and high efficiency voltage conversion. The thesis analyses the proposed converter structure through a dual buck-boost converter topology. The structure allows different converter topologies and combinations of them for different applications to be configured. The study begins with a motivation and a literature review of dc/dc converters. The new family of high step-up converters is introduced with an interleaved buck-boost as an example, followed by small-signal analysis. Experimental verifications, conclusions and future work are discussed

    Analysis of a new family of DC-DC converters with input-parallel output-series structure

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    There is an increasing trend of development and installation of switching power supplies due to their highly efficient power conversion, fast power control and high quality power conditioning for applications such as renewable energy integration and energy storage management systems. In most of these applications, high voltage conversion ratio is required. However, basic switching converters have limited voltage conversion ratio. There has been much research into development of high gain power converters. While most of the reported topologies focus on high gain and high efficiency, in this thesis, the input and output ripple currents and reliability are also considered to derive a new converter structure suitable for high step-up voltage conversion applications. High ripple currents and voltages at the input and output of dc-dc converters are not desirable because they may affect the operation of the dc source or the load. A number of converters operating in an interleaved manner can reduce these ripples. This thesis proposes a dc/dc switching converter structure which is capable of reducing the ripple problem through interleaved action, in addition to high gain and high efficiency voltage conversion. The thesis analyses the proposed converter structure through a dual buck-boost converter topology. The structure allows different converter topologies and combinations of them for different applications to be configured. The study begins with a motivation and a literature review of dc/dc converters. The new family of high step-up converters is introduced with an interleaved buck-boost as an example, followed by small-signal analysis. Experimental verifications, conclusions and future work are discussed

    Assessment of novel power electronic converters for drives applications

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    Phd ThesisIn the last twenty years, industrial and academic research has produced over one hundred new converter topologies for drives applications. Regrettably, most of the published work has been directed towards a single topology, giving an overall impression of a large number of unconnected, competing techniques. To provide insight into this wide ranging subject area, an overview of converter topologies is presented. Each topology is classified according to its mode of operation and a family tree is derived encompassing all converter types. Selected converters in each class are analysed, simulated and key operational characteristics identified. Issues associated with the practical implementation of analysed topologies are discussed in detail. Of all AC-AC conversion techniques, it is concluded that softswitching converter topologies offer the most attractive alternative to the standard hard switched converter in the power range up to 100kW because of their high performance to cost ratio. Of the softswitching converters, resonant dc-link topologies are shown to produce the poorest output performance although they offer the cheapest solution. Auxiliary pole commutated inverters, on the other hand, can achieve levels of performance approaching those of the hard switched topology while retaining the benefits of softswitching. It is concluded that the auxiliary commutated resonant pole inverter (ACPI) topology offers the greatest potential for exploitation in spite of its relatively high capital cost. Experimental results are presented for a 20kW hard switched inverter and an equivalent 20kW ACPI. In each case the converter controller is implanted using a digital signal processor. For the ACPI, a new control scheme, which eliminates the need for switch current and voltage sensors, is implemented. Results show that the ACPI produces lower overall losses when compared to its hardswitching counterpart. In addition, device voltage stress, output dv/dt and levels of high frequency output harmonics are all reduced. Finally, it is concluded that modularisation of the active devices, optimisation of semiconductor design and a reduction in the number of additional sensors through the use of novel control methods, such as those presented, will all play a part in the realisation of an economically viable system.Research Committee of the University of Newcastle upon Tyn

    Investigation of FACTS devices to improve power quality in distribution networks

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    Flexible AC transmission system (FACTS) technologies are power electronic solutions that improve power transmission through enhanced power transfer volume and stability, and resolve quality and reliability issues in distribution networks carrying sensitive equipment and non-linear loads. The use of FACTS in distribution systems is still in its infancy. Voltages and power ratings in distribution networks are at a level where realistic FACTS devices can be deployed. Efficient power converters and therefore loss minimisation are crucial prerequisites for deployment of FACTS devices. This thesis investigates high power semiconductor device losses in detail. Analytical closed form equations are developed for conduction loss in power devices as a function of device ratings and operating conditions. These formulae have been shown to predict losses very accurately, in line with manufacturer data. The developed formulae enable circuit designers to quickly estimate circuit losses and determine the sensitivity of those losses to device voltage and current ratings, and thus select the optimal semiconductor device for a specific application. It is shown that in the case of majority carrier devices (such as power MOSFETs), the conduction power loss (at rated current) increases linearly in relation to the varying rated current (at constant blocking voltage), but is a square root of the variable blocking voltage when rated current is fixed. For minority carrier devices (such as a pin diode or IGBT), a similar relationship is observed for varying current, however where the blocking voltage is altered, power losses are derived as a square root with an offset (from the origin). Finally, this thesis conducts a power loss-oriented evaluation of cascade type multilevel converters suited to reactive power compensation in 11kV and 33kV systems. The cascade cell converter is constructed from a series arrangement of cell modules. Two prospective structures of cascade type converters were compared as a case study: the traditional type which uses equal-sized cells in its chain, and a second with a ternary relationship between its dc-link voltages. Modelling (at 81 and 27 levels) was carried out under steady state conditions, with simplified models based on the switching function and using standard circuit simulators. A detailed survey of non punch through (NPT) and punch through (PT) IGBTs was completed for the purpose of designing the two cascaded converters. Results show that conduction losses are dominant in both types of converters in NPT and PT IGBTs for 11kV and 33kV systems. The equal-sized converter is only likely to be useful in one case (27-levels in the 33kV system). The ternary-sequence converter produces lower losses in all other cases, and this is especially noticeable for the 81-level converter operating in an 11kV network

    Two new families of high-gain DC-DC power electronic converters for DC-microgrids

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    Distributing the electric power in dc form is an appealing solution in many applications such as telecommunications, data centers, commercial buildings, and microgrids. A high gain dc-dc power electronic converter can be used to individually link low-voltage elements such as solar panels, fuel cells, and batteries to the dc voltage bus which is usually 400 volts. This way, it is not required to put such elements in a series string to build up their voltages. Consequently, each element can function at it optimal operating point regardless of the other elements in the system. In this dissertation, first a comparative study of dc microgrid architectures and their advantages over their ac counterparts is presented. Voltage level selection of dc distribution systems is discussed from the cost, reliability, efficiency, and safety standpoints. Next, a new family of non-isolated high-voltage-gain dc-dc power electronic converters with unidirectional power flow is introduced. This family of converters benefits from a low voltage stress across its switches. The proposed topologies are versatile as they can be utilized as single-input or double-input power converters. In either case, they draw continuous currents from their sources. Lastly, a bidirectional high-voltage-gain dc-dc power electronic converter is proposed. This converter is comprised of a bidirectional boost converter which feeds a switched-capacitor architecture. The switched-capacitor stage suggested here has several advantages over the existing approaches. For example, it benefits from a higher voltage gain while it uses less number of capacitors. The proposed converters are highly efficient and modular. The operating modes, dc voltage gain, and design procedure for each converter are discussed in details. Hardware prototypes have been developed in the lab. The results obtained from the hardware agree with those of the simulation models. --Abstract, page iv

    Multiport DC-DC Converters for Hybrid Energy Systems

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    Renewable energy sources (RESs) like solar and wind have gained attention for their potential to reduce reliance on fossil fuels and mitigate climate change. However, integrating multiple RESs into a power grid is challenging due to their unpredictable nature. Power electronic converters can manage hybrid energy systems by controlling power flow between RESs, storages, and the grid. Conventional single input dc-dc converters have limitations such as low efficiency, bulky designs, and complex control systems. Multiport dc-dc converters (MPCs) have emerged as a solution for hybridizing multiple sources, storages, and load systems by providing a common interface. Existing MPCs have limitations such as high component count, limited operational range, complex control strategies and restrictions on the number of inputs to list a few. Thus, there is a need to develop new MPCs that combine the advantages of existing designs while overcoming their limitations. Isolated MPCs with unipolar or bipolar outputs are needed that can accommodate any number of inputs, offer high voltage gain, use fixed magnetic components for galvanic isolation (regardless of the number of ports), and have a simplified control strategy. Additionally, new non-isolated MPCs with unipolar or bipolar outputs are required, featuring reduced component count, simultaneous power transfer and power flow between input ports, high voltage gain, low control complexity, and modular design allowing for arbitrary increase in the number of input ports. There is also an opportunity to apply MPCs in the integration of RESs and storages to ac grids through multilevel inverters for low component count, high efficiency, low harmonics, and higher power density. Further, advances in bipolar MPCs provide the chance to balance the dc bus without requiring a complex control system.acceptedVersio

    IMPROVEMENT STUDY ON SOFT-SWITCHED QUASI-RESONANT DC/DC BOOST CONVERTER

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    This report describes a novel soft-switched quasi-resonant DC/DC boost converter. Recently, remarkable efforts have been made in soft-switched quasi-resonant DC/DC converters to reduce losses and improve power efficiency. This project presents a new technique and it had improved the performance of the most recent study on soft-switched quasi-resonant DC/DC boost converter, which is presented in Ba-Thunya and Prasad's study [1]. The proposed converter employs an active snubber circuit with an auxiliary switch in series with a clamp capacitor to reduce powerlosses in Ba-Thunya and Prasad's original an active snubber circuit with an auxiliary switch and a clamp diode to reduce power losses in Ba-Thunya and Prasad's original converter. The energy from the snubber inductor after the auxiliary switch turn-off is returned to the input or delivered to the output via the active snubber circuit, thus the voltage stress onthe main switch is reduced and switching losses are minimized. Furthermore, the proposed converter reduces the reverse-recovery-related losses of the boost rectifier by controlling the di/dt rate of the rectifier current with the snubber inductor. This report describes the principle of operation of the new soft-switched quasi-resonant DC/DC boost converter. The feasibility study of the proposed converter is investigated using PSPICE program
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