Recent Advances and Industrial Applications of Multilevel Converters多电平变换器的经典综述

1、IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, VOL. 57, NO. 8, AUGUST 20102553Recent Advances and Industrial Applications of Multilevel ConvertersSamir Kouro, Member, IEEE, Mariusz Malinowski, Senior Member, IEEE, K. Gopakumar, Senior Member, IEEE, Josep Pou, Member, IEEE, Leopoldo G. Franquelo, Fello

2、w, IEEE, Bin Wu, Fellow, IEEE, Jose Rodriguez, Senior Member, IEEE, Marcelo A. Prez, Member, IEEE, and Jose I. Leon, Member, IEEEAbstractMultilevel converters have been under research and development for more than three decades and have found success-ful industrial application. However, this is stil

3、l a technology under development, and many new contributions and new commercial topologies have been reported in the last few years. The aim of this paper is to group and review these recent contributions, in order to establish the current state of the art and trends of the technology, to provide re

4、aders with a comprehensive and insightful review of where multilevel converter technology stands and is heading. This paper first presents a brief overview of well-established multilevel converters strongly oriented to their current state in industrial ap-plications to then center the discussion on

5、the new converters that have made their way into the industry. In addition, new promising topologies are discussed. Recent advances made in modulation and control of multilevel converters are also addressed. A great part of this paper is devoted to show nontraditional applications powered by multile

6、vel converters and how multilevel converters are becom-ing an enabling technology in many industrial sectors. Finally, some future trends and challenges in the further development of this technology are discussed to motivate future contributions that address open problems and explore new possibiliti

7、es.Index TermsActive filters (AFs), control, Flexible AC Trans-mission Systems (FACTS), high-power applications, high-voltage direct-current (HVDC) transmission, marine propulsion, modu-lation, multilevel converters, photovoltaic systems, train traction, wind energy conversion.Manuscript received Ja

8、nuary 26, 2010; revised February 24, 2010; accepted April 3, 2010. Date of publication June 7, 2010; date of current version July 14, 2010. This work was supported in part by the Chilean National Fund of Sci-entific and Technological Development (FONDECYT) under Grant 1080582, by the Centro Cientifi

9、co-Tecnologico De Valparaiso (CCTVal) NFB0821, by Ryerson University, by the European Union in the framework of European Social Fund through the Center for Advanced Studies Warsaw University of Technology, and by the Ministerio de Ciencia y Tecnologa of Spain under Project ENE2007-67033-C03-00.S. Ko

10、uro and B. Wu are with the Department of Electrical and Computer Engineering, Ryerson University, Toronto, ON M5B 2K3, Canada (e-mail: ; bwuee.ryerson.ca).M. Malinowski is with the Institute of Control and Industrial Electron-ics, Warsaw University of Technology, 00-662 Warsaw, Po

11、land (e-mail: .pl).K. Gopakumar is with the Centre for Electronics Design and Tech-nology, Indian Institute of Science, Bangalore 560 012, India (e-mail: kgopacedt.iisc.ernet.in).J. Pou is with the Department of Electronic Engineering, Technical Univer-sity of Catalonia, 08222 Terras

12、sa, Spain (e-mail: ).L. G. Franquelo and J. I. Leon are with the Department of Elec-tronics Engineering, University of Seville, 41092 Seville, Spain (e-mail: leopoldogte.esi.us.es; jileonzipi.us.es).J. Rodriguez and M. A. Prez are with the Department of Electronics Engineering, Univers

13、idad Tcnica Federico Santa Mara, 2390123 Valparaso, Chile (e-mail: jrpusm.cl; marcelo.perezusm.cl).Color versions of one or more of the figures in this paper are available online at .Digital Object Identifier 10.1109/TIE.2010.2049719I. INTRODUCTIONMULTILEVEL converters are f

14、inding increased attention in industry and academia as one of the preferred choices of electronic power conversion for high-power applications110. They have successfully made their way into the in-dustry and therefore can be considered a mature and proven technology. Currently, they are commercializ

15、ed in standard and customized products that power a wide range of applications, such as compressors, extruders, pumps, fans, grinding mills, rolling mills, conveyors, crushers, blast furnace blowers, gas turbine starters, mixers, mine hoists, reactive power compen-sation, marine propulsion, high-vol

16、tage direct-current (HVDC) transmission, hydropumped storage, wind energy conversion, and railway traction, to name a few 110. Converters for these applications are commercially offered by a growing group of companies in the field 1126.Although it is an enabling and already proven technology, multil

17、evel converters present a great deal of challenges, and even more importantly, they offer such a wide range of pos-sibilities that their research and development is still growing in depth and width. Researchers all over the world are contributing to further improve energy efficiency, reliability, po

18、wer density, simplicity, and cost of multilevel converters, and broaden their application field as they become more attractive and competi-tive than classic topologies.Recently, many publications have addressed multilevel con-verter technology and stressed the growing importance of mul-tilevel conve

19、rters for high-power applications 49. These works have a survey and tutorial nature and cover in depth traditional and well-established multilevel converter topologies, such as the neutral point clamped (NPC), cascaded H-bridge (CHB), and flying capacitor (FC), as well as the most used modulation me

20、thods. Instead, this paper presents a technology review, which is focused mainly on the most recent advances made in this field in the past few years, covering new promising topologies, modulations, controls, and operational issues. In ad-dition, one of the most interesting topics in multilevel conv

21、erter technology is the rapidly increasing and diverse application field, which is addressed in this work as well. In addition, emerging trends, challenges, and possible future directions of the development in multilevel converter technology are outlined to motivate further work in this field.This p

22、aper is organized as follows: First, a brief overview of classic multilevel topologies is presented in Section II to introduce basic concepts needed throughout this paper. This0278-0046/$26.00 2010 IEEE2554IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, VOL. 57, NO. 8, AUGUST 2010is followed by a revie

23、w of recent advances in multilevel con-verter topologies in Section III, where those already found in practice and those currently under development are addressed. Section IV covers the latest developments in multilevel mod-ulation methods. Latest contributions on multilevel converter control and di

24、fferent operational issues, such as capacitor voltage balance and fault-tolerant operation, are reviewed in Section V. New and future promising applications of multilevel converters are described in Section VI. Finally, in Section VII, future trends and challenges of multilevel converter technology

25、are discussed, which is followed by concluding remarks in Section VIII.II. CLASSIC MULTILEVEL TOPOLOGIES OVERVIEWFor completeness and better understanding of the advances in multilevel technology, it is necessary to cover classic mul-tilevel converter topologies. However, in order to focus the conte

26、nt of this paper on the most recent advances and ongoing research lines, well-established topologies will only be briefly introduced and referred to existing literature. In the following, classic topologies will be referred to those that have extensively been analyzed and documented and have been co

27、mmercialized and used in practical applications for more than a decade.Multilevel converter technology started with the introduc-tion of the multilevel stepped waveform concept with a series-connected H-bridge, which is also known as cascaded H-Bridge converter, in the late 1960s 27. This was closel

28、y followed by low-power development of an FC topology the same year 28. Finally, in the late 1970s, the diode-clamped converter (DCC) 29 was first introduced. The DCC concept evolved into the three-level NPC (3L-NPC) converter we know today as it was proposed in 3032 and can be considered as the fir

29、st real multilevel power converter for medium-voltage applications. Later, the CHB would be reintroduced in the late 1980s 33, although it would reach more industrial relevance in the mid-1990s 34. In the same way, the early concept of the FC circuit introduced for low power in the 1960s developed i

30、nto the medium-voltage multilevel converter topology we know to-day in the early 1990s 35. Through the years, the FC has also been reported as the imbricated-cell and multicell converter. (The latter is also a name used for the CHB since both are modular and made by interconnection of power cells.)T

31、hese three multilevel converter topologies could be consid-ered now as the classic or traditional multilevel topologies that first made it into real industrial products during the last two decades. The power circuits of a single-phase leg of these three topologies are shown in Fig. 1, featuring the

32、corresponding commonly used semiconductor device. These converters are commercialized by several manufacturers in the field 1126, offering different power ratings, front-end configurations, cool-ing systems, semiconductor devices, and control schemes, among other technical specifications. The most r

33、elevant pa-rameters and ratings for each of these classic topologies are listed in Table I. The parameters for each category are given for the different manufacturers, whose corresponding reference is given at the bottom of the table. As can be observed from the table, the 3L-NPC and the CHB are the

34、 most popular multilevelFig. 1.Classic multilevel converter topologies (with only one phase shown).(a) 3L-NPC featuring IGCTs. (b) Three-level FC featuring MV-IGBTs.(c) Five-level CHB featuring LV-IGBTs.topologies used in the industry. It is not straightforward or fair to compare the commercially av

35、ailable 3L-NPC with the 7L-to 17L-CHB listed in Table I since the first will have worse power quality and the second will have a more complex circuit structure. However, some evident differences between them can be concluded from Table I.1) The NPC features medium-/high-voltage devices inte-grated g

36、ate-commutated thyristor (IGCT) and medium-voltage/high-voltage insulated-gate bipolar transistors (IGBTs), whereas the CHB exclusively uses low-voltage IGBTs (LV-IGBTs).2) The CHB reaches higher voltage and higher power levels.3) The NPC is definitely more suitable for back-to-back regenerative app

37、lications. The CHB needs substantially higher number of devices to achieve a regenerative option (a three-phase two-level voltage source inverter (VSI) per cell).4) The CHB needs a phase-shifting transformer usually to conform a 36-pulse rectifier system. This is more expen-sive but improves input p

38、ower quality.5) The NPC has a simpler circuit structure, leading to a smaller footprint.6) Although both topologies generate the same amount of levels when using the same number of power switches, commercially available CHBs have more output voltage levels (up to 17, compared with three for the NPC)

39、. Hence, lower average device switching frequencies are possible for the same output voltage waveform quality. Therefore, air cooling and higher fundamental output frequency can be achieved without derating and without use of an output filter.These multilevel voltage source converter topologies belo

40、ng to the medium-voltagehigh-power converter family, whose classification is shown in Fig. 2. Note that, generally speaking, the medium-voltage range is considered in the power converter industry from 2.3 to 6.6 kV and high power in the range of 150 MW. The classification also includes direct acac c

41、onverters and current source converters, which are currently the main competitors of multilevel technology: mainly the cycloconverter and load commutated inverters (LCIs) for very high power, high-torque, and low-speed applications, and theKOURO et al.: RECENT ADVANCES AND INDUSTRIAL APPLICATIONS OF

42、 MULTILEVEL CONVERTERS2555TABLE ICLASSIC MULTILEVEL TOPOLOGY COMMERCIAL RATINGS AND SPECIFICATIONSFig. 2.Multilevel converter classification.pulsewidth-modulated current source inverter for high-power variable-speed drives. Other multilevel converter topologies also appear in this classification, so

43、me of which have recently found practical application and will be discussed later in this paper.Operating principles, multilevel waveform generation, spe-cial characteristics, modulation schemes, and other information related to the NPC, FC, and CHB can be found with plenty of details and useful ref

44、erences to previous works in 29 and therefore will not be covered in this paper devoted to the present research topics.A number of papers have recently been published compar-ing the three topologies for specific applications in terms ofthe losses and the output voltage quality 3638. A few conclusion

45、s from these papers are worth mentioning. The 3L-NPC has become quite popular because of a simple transformer rectifier power circuit structure, with a lower device count when considering both the inverter and rectifier, and less number of capacitors. Although the NPC structure can be extended to hi

46、gher number of levels, these are less attractive because of higher losses and uneven distribution of losses in the outer and inner devices 5. In particular, the clamping diodes, which have to be connected in series to block the higher voltages, introduce more conduction losses and produce reverse re

47、covery currents during commutation that affects the switching losses of the other devices even more. Furthermore, dc-link capacitor voltage balance becomes unattainable in higher level topologies with a passive front end when using conventional modulation strategies 3941. In this case, the classic m

48、ultilevel stepped waveform cannot be retained, and higher dv/dts (more-than-one-level transitions) is necessary to balance the capacitors for certain modulation indexes.On the other hand, the CHB is well suited for high-power ap-plications because of the modular structure that enables higher voltage

49、 operation with classic low-voltage semiconductors. The phase shifting of the carrier signals moves the frequency har-monics to the higher frequency side, and this, together with the high number of levels, enables the reduction in the average de-vice switching frequency ( 500 Hz), allowing air cooli

50、ng and lower losses. However, it requires a large number of isolated dc sources, which have to be fed from phase-shifting isolation transformers, which are more expensive and bulky, compared with the standard transformer used for the NPC. Nevertheless, this has effectively been used to improve the i

51、nput power factor of this converter, reducing input current harmonics.Although the FC is modular in structure, like the CHB, it has found less industrial penetration, compared to the NPC and CHB, mainly because higher switching frequencies are2556IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, VOL. 57,

52、 NO. 8, AUGUST 2010Fig. 3.Three-phase 5L-HNPC 4244.necessary to keep the capacitors properly balanced, whether a self-balancing or a control-assisted balancing modulation method is used (e.g., greater than 1200 Hz) 5. These switching frequencies are not feasible for high-power applications, where us

53、ually they are limited in a range of 500700 Hz. This topol-ogy also requires initialization of the FC voltages.III. RECENT ADVANCES IN TOPOLOGIESSince the introduction of the first multilevel topologies al-most four decades ago 27, perhaps dozens of variants and new multilevel converters have been p

54、roposed in literature. Most of them are variations to the three classic multilevel topologies, discussed in the previous section, or hybrids between them. However, not so many have made their way to the industry yet. Among the newer topologies that currently have found practical application are the

55、following: the five-level H-bridge NPC (5L-HNPC), the three-level active NPC (3L-ANPC), the five-level active NPC (5L-ANPC), the modular multilevel converter (MMC), and the cascaded matrix converter (CMC). Apart from these, several other topologies have been proposed and are currently under developm

56、ent, among which are the following: the transistor-clamped converter (TCC), the CHB fed with unequal dc sources or asymmetric CHB, the cascaded NPC feeding open-end loads, the hybrid NPC-CHB and hybrid FC-CHB topologies, and the stacked FC or stacked multicell, to name a few. All these topologies ar

57、e addressed in the following sections and can be found in the medium-voltage converter classification of Fig. 2.A. 5L-HNPCThis converter is composed of the H-bridge connection of two classic 3L-NPC phase legs, as shown in Fig. 3, forming a 5L-HNPC converter, and was first introduced in 45. This topo

58、logy has been commercialized by two medium-voltage drive manufacturers 11, 13 and has received increased at-tention over the years 4244.The combination of the three levels of each leg of the NPC (Vdc/2, 0, Vdc/2) results in five different output levels (Vdc, Vdc/2, 0, Vdc/2, Vdc). As with the traditional H-bridge, this topology requires an isolated