[雙語翻譯]--外文翻譯--模塊化多電平變換器（mmc）的脈沖寬度調(diào)制的實驗和控制（原文）

1、IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 24, NO. 7, JULY 2009 1737Control and Experiment of Pulsewidth-ModulatedModular Multilevel ConvertersMakoto Hagiwara, Member, IEEE, and Hirofumi Akagi, Fellow, IEEEAbstract—A m

2、odular multilevel converter (MMC) is one ofthe next-generation multilevel converters intended for high- or medium-voltage power conversion without transformers. The MMC is based on cascade connection of multiple bidirect

3、ional chopper-cells per leg, thus requiring voltage-balancing control of the multiple floating dc capacitors. However, no paper has made an explicit discussion on voltage-balancing control with theoretical and experiment

4、al verifications. This paper deals with two types of pulsewidth-modulated modular multilevel converters (PWM- MMCs) with focus on their circuit configurations and voltage- balancing control. Combination of averaging and

5、balancing con- trols enables the PWM-MMCs to achieve voltage balancing without any external circuit. The viability of the PWM-MMCs, as well as the effectiveness of the voltage-balancing control, is confirmed by simulatio

6、n and experiment.Index Terms—Medium-voltage power conversion, multilevelconverters, voltage-balancing control.I. INTRODUCTIONHIGH-POWER converters for utility applications require line-frequency transformers for the purp

7、ose of enhanc-ing their voltage or current rating [1]–[4]. The 80-MVA Static synchronous Compensator (STATCOM) commissioned in 2004 consists of 18 neutral-point-clamped (NPC) converter legs [4], where each of the ac side

8、s is connected in series by the corre- sponding transformer. The use of line-frequency transformers, however, not only makes the converter heavy and bulky, but also induces the so-called dc magnetic flux deviation when a

9、 single-line-to-ground fault occurs [5].Recently, many scientists and engineers of power systemsand power electronics have been involved in multilevel convert- ers intended for achieving medium-voltage power conversion w

10、ithout transformers [6]–[8]. Two of the representatives are:1) the diode-clamped multilevel converter (DCMC) [6], [7]; 2) the flying-capacitor multilevel converter (FCMC) [8]. The three-level DCMC, or a NPC converter [9]

11、 has been putinto practical use [10]. If a voltage-level number is more than three in the DCMC, inherent voltage imbalance occurs in the series-connected dc capacitors, thus resulting in requiring an external balancing c

12、ircuit (such as a buck–boost chopper) for a pair of dc capacitors [11]. Furthermore, a significant increase in the clamping diodes required renders assembling and build- ing of each leg more complex and difficult. Thus,

13、a reasonable voltage-level number would be up to five from a practical pointManuscript received July 16, 2008; revised October 16, 2008. Current versionpublished July 22, 2009. Recommended for publication by Associate Ed

14、itor S. Bhattacharya.The authors are with the Department of Electrical and Electronic Engineering,Tokyo Institute of Technology, 152-8552 Tokyo, Japan (e-mail: mhagi@akg. ee.titech.ac.jp; akagi@ee.titech.ac.jp).Digital O

15、bject Identifier 10.1109/TPEL.2009.2014236Fig. 1. Circuit configuration of a chopper-cell-type modular multilevel in-verter: (a) Power circuit, and (b) Bidirectional PWM chopper-cell with a floating dc capacitor.of view.

16、 As for the FCMC, the four-level pulsewidth modulation (PWM) inverter is currently produced by one manufacture of in- dustrial medium-voltage drives [12]. However, the high expense of flying capacitors at low carrier fre

17、quencies (say, lower than 1 kHz) is the major disadvantage of the FCMC [13].A modular multilevel converter (MMC) has been proposedin [14]–[20], intended for high-power applications. Fig. 1 shows a basic circuit configura

18、tion of a three-phase modular multilevel inverter. Each leg consists of two stacks of multiple bidirectional cascaded chopper-cells and two noncoupled buffer inductors. The MMC is suitable for high- or medium-voltage pow

19、er con- version due to easy construction/assembling and flexibility in converter design. Siemens has a plan of putting it into practical use with the trade name of “high-voltage direct current (HVDC)- plus.” It is report

20、ed in [19] that a system configuration of the HVDC-plus has a power rating of 400 MVA, a dc-link voltage of ±200 kV, and 200 cascaded chopper cells per leg. The au- thors of [14]–[20], however, have made no detailed

21、 description of staircase modulation, especially about a crucial issue of how to achieve voltage balancing of 200 floating dc capacitors per leg. Moreover, no experimental result has been reported yet.0885-8993/$26.00 &#

22、169; 2009 IEEEHAGIWARA AND AKAGI: CONTROL AND EXPERIMENT OF PULSEWIDTH-MODULATED MODULAR MULTILEVEL CONVERTERS 1739Fig. 4. Block diagram of dc-capacitor voltage control: (a) Averaging control,and (b) Balancing control.No

23、te that iP u, iN u, iu, and id are branch currents whereas iZ u is a loop current that is impossible to measure directly.III. CONTROL METHOD OF THE MMCThe voltage-balancing control of eight floating dc capacitorsper leg

24、in Fig. 1 can be divided into:1) averaging control; and 2) balancing control.A. Averaging ControlFig. 4(a) shows a block diagram of the averaging control. Itforces the u-phase average voltage ¯ vC u to follow its co

25、mmandv?C , where ¯ vC u is given by¯ vC u = 188 ?j=1vC ju. (3)Let a dc-loop current command of iZ u be i?Z u, as shown inFig. 4(a). It is given byi? Z u = K1(v?C ? ¯ vC u) + K2?(v?C ? ¯ vC u) dt. (4)T

26、he voltage command obtained from the averaging control, v?Auis given byv?Au = K3(iZ u ? i?Z u) + K4?(iZ u ? i?Z u) dt. (5)When v?C ≥ ¯ vC u, i?Z u increases. The function of the currentminor loop in Fig. 4(a) forces

27、 the actual dc-loop current iZ u to follow its command i?Z u. As a result, this feedback controlof iZ u enables ¯ vC u to follow its command v?C without beingaffected by the load current iu.B. Balancing ControlThe u

28、se of the balancing control described in [21] forces theindividual dc voltage to follow its command v?C . Fig. 4(b) showsa block diagram of the u-phase balancing control, where v?B ju isthe voltage command obtained from

29、the balancing control. Since the balancing control is based on either iP u or iN u, the polarityFig. 5. Voltage command of each arm: (a) Positive arm, and (b) Negative arm.of v?B ju should be changed according to that of

30、 iP u or iN u.When v?C ≥ vC ju (j : 1 ? 4) in the positive arm of Fig. 1(a), apositive active power should be taken from the dc power supply into the four chopper-cells. When iP u is positive, the product of vB ju (= v?B

31、 ju) and iP u forms the positive active power. WheniP u is negative, the polarity of vB ju should get inverse to take the positive active power. Finally, v?B ju for j = 1 ? 4 is representedasv?B ju =? K5(v?C ? vC ju) (iP

32、 u > 0)?K5(v?C ? vC ju) (iP u 0)?K5(v?C ? vC ju) (iN u < 0). (7)Fig. 5 shows a voltage command of each chopper-cell v?ju.The positive-arm and negative-arm commands are obtained as:v?ju = v?Au + v?B ju ? v?u 4 + E8

33、 (j : 1 ? 4) (8)v?ju = v?Au + v?B ju + v?u 4 + E8 (j : 5 ? 8) (9)where v?u is an ac-voltage command for the u-phase load. Notethat Fig. 5 includes the feedforward control of the dc supply voltage E. The voltage command v

34、?ju is normalized by eachdc-capacitor voltage vC ju, followed by comparison with a tri- angular waveform having a maximal value of unity and a min- imal value of zero with a carrier frequency of fC . The actual switching

35、 frequency of each chopper-cell, fS is equal to fC . The eight chopper-cells have the eight triangular waveforms with the same frequency but a phase difference of 45? (= 360?/8) to each other for achieving harmonic cance

36、llation and enhancing cur- rent controllability. As a result, the line-to-neutral voltage is a nine-level voltage waveform, and a line-to-line voltage is a 17- level voltage waveform with an equivalent switching frequenc

37、y of 8fC .C. Simulated ResultsFig. 6 shows simulated waveforms from Fig. 1. Tables I and IIsummarize circuit parameters and control gains used for simu- lation using a software package of the “PSCAD/EMTDC” [24]. The dc s