Low-Loss HVDC Transmission System With Self-commutated Power Converter Introducing Zero-current...

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Published in IET Generation, Transmission & Distribution

Received on 13th February 2008

Revised on 7th October 2008

doi: 10.1049/iet-gtd.2008.0078

ISSN 1751-8687

Low-loss HVDC transmission system with self-

commutated power converter introducingzero-current soft-switching technique

T. Senjyu K. Kurohane J. Miyagi N. UrasakiFaculty of Engineering, University of the Ryukyus, 1 Senbaru, Nishihara-cho, Nakagami, Okinawa 903-0213, JapanE-mail: [email protected]

Abstract: In recent years, application of self turn-off devices for the HVDC transmission system is very important

for flexible and high efficient power transport and supply. However, for self turn-off devices that are applied to

high-power system, excessive switching losses due to voltage/current surges occurred on hard switching and thecurrent tail characteristics on turn-off lead to the considerable switching loss. Therefore switching-loss reduction

by using a soft-switching technique is very effective for improvement of the considerable switching losses. A self-

commutated HVDC circuit topology with soft-switching characteristics is discussed. The proposed topology is able

to achieve a zero-current switching in self-commutated power converters. In order to examine the effectiveness

of the proposed system, the system is analysed in terms of the characteristics of switching losses through a

theoretical approach and computer simulations.

1 Introduction

Recently, HVDC transmission technology has been widelyapplied in some countries because of the advantage of itseconomical efficiency, power system stability and load flowcontrol. The ACDC power converters are indispensablein HVDC transmission systems and mostly consist ofthyristors on line-commutated devices. In recent years, the

usage of flexible and efficient power control and transfer byuse of self turn-off devices for HVDC power convertershave been increasing. However, self turn-off devices such asgate turn-off thyristor (GTO) and insulated gate bipolartransistor (IGBT) have some limitations. These limitationsinclude the increase in voltage/current stress and highswitching losses, rising heat of converters and thegeneration of electromagnetic noise.

The solutions for these problems include improvement ofperformances of power semiconductors and circuit topology.

The former method means technical advantages for power

devices using the siliconcarbide (SiC) process technology, which replaces the silicon (Si) process technology[1, 2],and the later method means an application of soft-

switching circuit topology based on resonance phenomenonusing L-C elements [39].

Soft-switching techniques are beneficial in reducing theswitching losses. In the past, several soft-switching circuittopologies for DCDC converters and ACDC converterson the power applications have been proposed [18]. DC-link circuit topology with zero-voltage switching (ZVS) as

DC DC converters have been reported in [35]. TheAC-link circuit topology with ZVS manner that envisionsthe charge and discharge of power energy is presented in[6]. The ZCS static var compensator circuit topologiesusing current-source-inverter have also been reported in[710]. Furthermore, studies on low-loss snubber circuit[11, 12] for improving the switching losses and voltage/current stresses have also been reported. However, a self-commutated HVDC system with soft-switching techniqueis skill unavailable.

The current tail characteristics greatly increase the

switching loss of the power converter. However, the ZCStechnique is capable of controlling the current tail thatflows to self turn-off devices by adding an auxiliary circuit.

IET Gener. Transm. Distrib., 2009, Vol. 3, Iss. 4, pp. 315 324 315

doi: 10.1049/iet-gtd.2008.0078 & The Institution of Engineering and Technology 2009

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Therefore ZCS is the most successful soft-switchingtechnique for application of high-power converters.Besides, the soft-switching technique contributes to thereduction of EMI noise. On the other hand, ZVS controls

voltage that occurs in the terminal of devices, and the voltage is cancelled by resonant operation. Therefore it isdifficult to decrease of the switching losses significantlycaused by the current tail based on ZVS is difficult. Alsothe resonant circuit is an additional circuit that increasesthe costs and power losses of components.

This paper proposes a zero-current switched HVDC circuittopology with self-commutated converter to improve theswitching loss of HVDC. The switching losses of HVDC arereduced by adding a commutation circuit. In order to verifythe effectiveness of the proposed system, the simulations arecarried on by using MATLAB/SIMULINK and

SimPowerSystems based on instantaneous modelling.

This recent paper is organised as follows. Circuitconfiguration and operating principle of the proposedsystem are given in Section 2. Section 3 shows ZCSrequirements for soft switching. To confirm the robustnessof the proposed circuit, fault simulations for soft-switchingHVDC are executed in Section 4. Section 5 analyses thecharacteristics of switching loss and conversion efficiencythrough a theoretical approach and computer simulations.Finally, conclusions are drawn in Section 6.

2 Circuit configuration andoperating principle

2.1 Circuit configuration of the proposedsystem

Replacing line-commutated devices to self turn-off devicescauses an increase in switching loss. Therefore this paperpresents a soft-switching HVDC circuit topology. Byconnecting commutation circuits for DC-link part of powerconverters, the proposed circuit executes the soft-switchingZCS. Fig. 1 shows the main configuration of the soft-

switching HVDC transmission system. The circuitconfiguration contains point-symmetry except the DC-line. The power system side consists of DC smoothing reactor,

commutation circuit, current source self-commutatedconverter, output capacitors, converter transformer, ACfilter and line impedances. The function of outputcapacitors Cac1, Cac2 is to keep the voltage by regulating thereactive power. A commutation circuit consists of twothyristors T1 and T2 (or T3 and T4), resonant capacitorCcr1(or Ccr2) and resonant inductors Lcr1 and Lcr2(or Lcr3 andLcr4). By connecting the commutation circuits for the DC-link, it is possible to achieve a perfect ZCS in HVDC.

That is to say, the commutation circuits aim to intermiticon1 and icon2 flowing to the power converters. Theoperating analysis of the commutation circuit is describedin detail in the next section.

2.2 Operating principle and analysisfor commutation circuit

Fig. 2 shows equivalent circuits in each mode (Mode 1Mode 6) of commutation-circuit operation. Since thesimulation results of the operated commutation circuits oneach side are nearly the same, only the right-side one isanalysed. The commutation circuit has six operating modesfor a changing cycle of switching devices, and the resonant-modes occur at Modes 1, 3 and 5. It is assumed that theDC current Idc1 flowing to converter is sufficientlysmoothed by the DC reactor. A thyristor model is treatedas the same as GTO thyristor model that is shown in theFig. 3. The equations needed for analysis of operation arederived on the basis of this figure.

Mode 1 (t02 t1: Fig. 2a): As the initial state in Mode 1,main-switches Up1 and Wn1 on the right-side converter andthyristor T2 on the commutation circuit are in theconduction state as shown in Fig. 2a. Other GTO devicesand thyristor are in off-state. In addition, the voltage vcr1 atboth ends of the resonant capacitorCcr1, are charged up to Vco.

In the beginning of this mode (t t0), when T2 is on by aturn-on signal, the commutation circuit attains resonantcondition by capacitor Ccr1 and inductor Lcr1. Then, theresonant current ir1 flows in the commutation circuit. The

ir1 has the resonant frequency g1 determined by resonantcapacitor and inductor. An equivalent circuit of Mode 1 isshown in Fig. 2a. The charging voltage of resonant capacitor

Figure 1 HVDC transmission system configuration with soft-switching technique

316 IET Gener. Transm. Distrib., 2009, Vol. 3, Iss. 4, pp. 315324

& The Institution of Engineering and Technology 2009 doi: 10.1049/iet-gtd.2008.0078

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Ccr1 begins to decrease by the flow of resonant currentir1. Themode condition shifts to next mode, Mode 2, when all icon1commutate to the commutation circuit.

The voltage equation with Mode 1 is given as

Vdc (RLr1Ron)ir1 (Lcr1 Lon)dir1dt

Vf

1Ccr1

ir1 dt Vco (1)

where RLr1 is the inner electrical resistance in resonantelement Lcr1. By solving the differential equation (1),

resonant current ir1 is expressed as

icon1 Idc ir1

Idc Ccr1V1vo1

2

g11a1t sinh g1t (2)

where V1 Vdc Vf Vco

a+ jb a1 + jffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffia1

2 vo12

p RLr1Ron2(Lon Lcr1)

+ j

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiRLr1 Ron

2(Lcr1 Lon)

2 1

Ccr1(Lcr1 Lon)

s

where a1 is a constant value and jbmeans the same angularfrequency as vo1 in resonant current ir1.

Mode 2(t12 t2: Fig. 2b): The converter current icon1commutates to the commutation circuit side, and theequivalent circuit in this mode is shown in Fig. 2b. When

icon1 flowing to the converter is zero, by switching Up1 andVp1, they are turned-off and turned-on at ZCS,respectively. After switching-on and switching-off the main

Figure 2 Equivalent circuits of each mode in commutated circuit

a Mode 1b Mode 2c Mode 3d Mode 4e Mode 5f Mode 6

Figure 3 Model diagram of GTO



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devices, the icon1 again begins to flow to the primary side, andthe operating mode shifts to Mode 3.

Mode 3 (t22 t3: Fig. 2c): Equivalent circuit of Mode 3 isshown in Fig. 2c. The commutation circuit once again is inresonant condition. As the voltage equation in Mode 3 is

similar to (1) of Mode 1, a equation of resonant current ir3and (2) are equivalent. In this mode, a resonant capacitorchanges in reverse polarity by the flow of ir3. When ir3 iszero, then thyristor T2 is turned-off with ZCS, and thecondition also shifts to Mode 4.

Mode 4 (t32 t4: Fig. 2d): Resonant current that is flowing tocommutation circuit is zero, and vcr1 has reverse polarity. Inthis mode, the DC (current) Idc1 flows to the primaryinverter. An equivalent circuit of Mode 4 is shown in Fig. 2d.

Mode 5 (t42 t5: Fig. 2e): To reverse the polarity of the

resonant capacitor voltage vcr1( Vco), a turn-on signalthat has time delay Tdelay later than the turn-on signal ofthyristor T2, is given to the thyristor T1. An equivalentcircuit of this mode is shown in Fig. 2e. By turning on T1,a resonant current ir5 that has reverse direction flows in thecommutation circuit, and vcr1 is charged in straight polarity.

The voltage equation ofFig. 2e is written as

Vco (RLr2 Ron)ir5 (Lon Lcr1 Lcr2)dir5dt

1Ccr1

ir5 dt

(3)

where RLr2 is inner electrical resistance in resonant elementLcr2. By solving the differential equation (3), the currentequation of Mode 5 is given as

ir5 Ccr1Vcovo5

2

g51a5t sinhg5t

is Idc

9=; (4)

where a+ jb a5 + j

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffia5

2 vo52

p RLr2 Ron

2(Lcr1 Lcr2 Lon)

+ j

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiRLr2 Ron

2(Lcr1 Lcr2 Lon)

2 1

Ccr1(Lcr1 Lcr2 Lon)

s

where a5 is a constant value and jbmeans the same angularfrequency as vo5 in resonant current ir5. When ir5 reacheszero, the operating mode shifts to Mode 6.

Mode 6 (t52 t00: Fig. 2e): In this mode, the resonant current

is zero, the equivalent circuit of Mode 6 is shown in Fig. 2f.When T2 has a turn-on signal, a commutation circuit repeatsthe similar operating modes from Mode 1.

2.3 Simulation key waveform on softand hard switchings

To confirm the operating characteristics of the proposed circuitshown in Fig. 1, the proposed system is simulated usingMATLAB/SIMULINK and SimPowerSystems. The

instantaneous simulation waveforms of a model with DC-lines are shown in Figs. 4 and 5. Fig. 4 shows simulationresults with soft-switching ZCS. To confirm effectiveness ofthe method, simulation results by hard switching are shownin Fig. 5. From Figs. 4 and 5, it is observed that iup1 and ivp1flowing to each device by soft switching become nearly zeroby operating the commutation circuit before the main devicesUp1 and Vp1 turn-off and turn-on, respectively. However, iup1and ivp1 by hard switching is not zero. As a result, excessiveswitching losses (losses more than 100 MW on turn-off andlosses of about 1.7 MW on turn-on), occur instantaneously inthe main devices on hard switching. On the contrary,

switching loss on soft switching is nearly zero. Therefore the voltage and current stresses can be reduced (more than100 MW on turn-off and about 1.7 MW on turn-on). Toevaluate the instantaneous switching loss on a simulation, aGTO arm model of converters consists of a series connectedto 15 devices (the nominal voltage and current in a GTOdevice are 6000 V and 6000 A, respectively).

Figure 4 Key waveforms with soft switching



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3 ZCS requirement for softswitching

In this section, the following description gives someconditional equations for a soft switching technique ZCSon the right-side power converter shown in Fig. 1, sinceZCS requirements on either side are the same.

3.1 ZCS requirement for resonantfrequency

The quality factor Q that refers to the sharpness of theresonant curve in LCR circuit (not the quality factorof a coil) is shown as

Q 1RL

ffiffiffiffiffiffiffiLroCcr

s(5)

In case of Modes 2 and 4

RL RLr1 RonLro Lcr1 Lon

In case of Mode 6

RL RLr2 RonLro Lcr1 Lcr2 Lon

where the quality factor Q means sharpness of resonantcurrent. The resonance phenomenon can be classified asfollows cases in terms ofQ

In case of

(1) Q. 1=2

(2) Q, 1=2

(3) Q 1=2

8>: ,

a resonant current has

(1) oscillatory behaviour

(2) non-oscillatory behaviour

(3) critical behaviour

8>:

With the above classification, resonant current must haveoscillatory behaviour for the soft switching. Therefore theconditional equation is then shown as

1

RL

ffiffiffiffiffiffiffiLroCr

s.

1

2(6)

3.2 Requirement of shunt-currenticon

Here, the maximum value of resonant current is derived. Incase of Q. 1=2, the variables need to be changed since g1in the resonant current (2) is imaginary. Asg

1 ib

1 iffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiv

o1

2

a

1

2p , then from (2), the resonantcurrent equation is expressed as

ir1 CcrV1vo1

2

b11a1t sinb1t (7)

Therefore the extreme solution (maximum value) of (7)becomes

Ir2peak V1

b1(Lcr1 Lon)1a1=b1f1 sinf1

{f1

tan1

a1

b1

(8)

A soft-switching technique ZCS is executed by turning-onand turning-off the IGBT main devices on the powerconverters when the converter current icon1 is zero. For thisreason, the maximum resonant current Ir2peak must be

Figure 5 Key waveforms with hard switching

Table 1 Simulation parameters (right-side only)

GTO 1 arm RGon 15 mV, LGon 15 mH, VIf 90 V

thyristor 1 arm RTon 28 mV, LTon 28mH, VTf 70 V

resonant components Lcr1 2mH, RLr1 2 mV, Lcr2 3mH, RLr2 3 mV, Ccr1 40mF, fr1 4:59 kHz, fr5 4:38 kHzcircuit parameters Ldc1 0:8 H, RLdc1 1:5V, Cac1 110mF; X1 82:94V



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Figure 6 HVDC model with fault

Figure 7 Three-phase voltage and current with terminal-fault

a Wave form for left converter-sideb Wave form for right converter-sidec Wave form for left source-side

d Wave form for right source-sidee Wave form for left DC line-sidef Wave form for right DC line-side



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bigger than the direct current Idc1 and can be expressed asfollows

Ir2peak V1

b1(Lcr1

2Lon)1a1=b1f1 sinf1 ! Idc1 (9)

3.3 Setting of time-delay Tdelay forcommutation-circuit operation

The time-delayTdelay, that is the interval time for turn-onsignals of thyristor elements in the commutation circuit,must be longer than the half-cycle of resonant frequencyb1

in Modes 1 and 3. Therefore Tdelay can be expressed as

Tdelay !Tr12 1

2fr1 pb1

pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffivo1

2 a12p (10)

where Tr1

mean time thatT1

is in resonant condition.

4 Fault simulation of HVDCcircuit with ZCS

To confirm the robustness of the proposed circuit, faultsimulations for soft-switching HVDC are executed. The

Figure 8 Three-phase voltage and current with ground fault

a Wave form for left converter-sideb Wave form for right converter-sidec Wave form for left source-side

d Wave form for right source-sidee Wave form for left DC line-sidef Wave form for right DC line-side



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parameters used in this simulation are shown inTable 1, whereLcr and Ccr was derived from (6). Each arm of the three-phasebridge is composed of 6000 V, 6000 A gate turn-off thyristorand 4500 V, 800 A anti-parallel diode. While, the resonantcircuit is composed of 3000 V inductances, 4000 V, 800 Athyristor, 2500 V capacitor. As for the other components, we

employ a 6600 V, 87.5 A, high-voltage phase advancecapacitor and a 420 kVA, 6600 V, 60 Hz AC filter.Regarding the voltage rating of the devices, it is possible toreduce the voltage rating of the devices with the increment ofthe number of L-C elements and series connection ofswitching devicies. The simulations assume terminal andthree phase to ground faults. Fig. 6 shows HVDC model

with faults. The simulation timestep is variable step (03 ms),duration of simulation is 0.5 s and time of execution is about17 min. The simulation sequence is as follows: fault on theright-side occurred at t 0.15 s, and each power converterstops. In addition, the fault in the power system recovers at

t

0.3 s for considering the time when the system recoversafter an accident occurred, and each converter operates. In thefault simulations, only the left-side converter is soft switching,

while the right-side is conventional switching.

Fig. 7 shows three-phase voltages and currents withterminal fault. From Figs. 7a, 7b and 7e, we can confirmthat the output current of stopped converters is equal to zerobecause of the terminal fault. Besides, after the fault in theright-side recovers at t 0.3 s for cosidering the time whenthe system recovers after an accident occurred, the powerconverter of the right-side operates again with soft switching.

Fig. 8 shows three phase voltages and currents with a threephase to ground fault. As can be seen from Fig. 8a, 8band 8e,that the ground fault occurs at t 0.15 s, the DC currentand three phase currents ia, ib and ic of converters side arezero, and left-side converter is switched with ZCS.

Note that DC-current idc1 is zero by operatingcommutation circuit, and the output AC-current is zero.

Thus the output current wave form of soft-switchedconverter (Figs. 7a and 8a) include many vertical lines thanfor no soft switching (Figs. 7b and 8b).

5 Evaluation of switching loss

By using the derived equations in the Appendix, thecharacteristics of switching loss for HVDC transmissioncircuit applied to self-commutated power converter isevaluated for theoretical values. The parameters used forthe circuit are shown in the Appendix. In addition, theequations for power losses with hard switching (on 1208conducting operation) are also derived in the Appendix.

The power-loss characteristics with soft switching are onlycomposed of conduction loss, because it is confirmed in

Fig. 9 that switching losses with turn-on and turn-off withsoft switching are nearly zero. The additional losses withcommutation circuit are included in the energy losses.

Fig. 9ashows the characteristics of switching losses for hard-switching HVDC. In Fig. 9a, the solid line and the chaindashed line show the total losses and the turn-off losses,respectively. The chain double-dashed line and the chainedline show the turn-on losses and the conduction losses,respectively. The dot line shows the transmission power. As

the main losses that occur in the self turn-off device aregenerally turn-on and turn-off losses and conduction losses,the above three switching losses are evaluated. As can be seenfrom Fig. 9a, with the increase of DC-currentIdc, such lossesare increasing. It can be confirmed that the arising losses onhard switching in a high-power system like HVDC systemare excessive, and that the switching losses in turn-off exceedconduction losses from Fig. 9a. Besides, it is confirmed thatthe increase in hard-switching losses for high-power HVDCcircuit is high, and the switching losses with turn-off arelarger than conduction loss.

Figure 9 Switching losses

a Hard-switching lossb Hard-switching loss ratioc Total switching-loss comparison



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Fig. 9bshows the proportions of such losses (turn-on andturn-off losses and conduction losses) to total losses (turn-on and turn-off losses conduction losses) as a percentage. In Fig. 9b, the chain dashed line and the chaindouble-dashed line show the characteristics of turn-offlosses, and turn-on losses respectively, whereas the chained

line and the dot line show conduction losses andtransmission power, respectively. From Fig. 9b, it isconfirmed that the losses with turning-off indicate lossesmore than 50% of total losses, and the turn-off losses withswitching dominate the huge percentage of total losses.From the above results, in large-scale power systems suchas HVDC system it is confirmed that energy lossesoccurring in self turn-off devices depend a lot onswitching loss.

Fig. 9cshows total loss of HVDC circuit with hard- andsoft switching, respectively. To confirm effectiveness of the

soft-switching technique, the total losses with hardswitching are compared with soft-switching HVDC at1208 conduction operation. The total loss with soft-switching HVDC includes copper and core losses withresonant-element coil, and conduction loss with thyristors.

The solid line and the dash line show the total losses(conduction loss loss of commutation circuit ) with softswitching and total losses (conduction loss turn-on andturn-off loss) with hard switching, respectively. FromFig. 9c, it is confirmed that switching losses with self turn-off devices are significantly improved by applying the soft-switching technique.

6 Conclusion

This paper proposes the HVDC circuit with soft-switchingtechnique. The proposed circuit concludes that switchinglosses with all self turn-off devices are nearly zero byconnecting commutation circuits for power converters. Inaddition, it is able to execute soft-switching ZCS only bydeciding switching sequences that turn-on pulsessynchronised with turn-on signals of main-devices GTOgive thyristor of commutation circuit. With the operatinganalysis of the proposed circuit, the analysis equations forsuch operating modes and ZCS requirements for soft

switching are derived. Besides, to confirm the robustness ofthe proposed circuit, fault simulations for soft-switchingHVDC are executed. The simulation results show that theproposed circuit can achieve soft-switching operation, afterfaults in the power system recover. Finally, to confirm theeffectiveness of soft-switching technique, the proposedcircuit is strictly modelled using MATLAB/SIMULINKand SimPowerSystems. Switching losses with 1208conduction operation are calculated on the simulationresults, and total losses for soft switching are compared

with them for hard-switching. As a result, it is confirmedthat the improvement of power losses are more than 50%

of total losses for hard-switching HVDC. Therefore the voltage and current stresses can be reduced. There are thetrade-off relationship between the increase of circuit

component parts with auxiliary commutation circuit andthe improvement of high power losses attributed byintroducing the soft-switching technique. However, for thereduction of switching losses confirmed from simulationresults, the additive losses in the commutation-circuit aregenerated and the voltage rating of the devise is a little

high, but the total losses in power converters for theproposed system is improved. It is sufficiently possible todecrease the power losses in the total system withapplication of soft-switching technique. In addition tothe above effectiveness, the cost reduction is led bydecreasing the heat-radiation unit with the reduction ofswitching loss.

Developments of self turn-off device technology need nosoft-switching techniques. However, there are facts that theabove developments advance soft switching and controltechnologies. Besides, there is no ideal switching device,

and the switching losses with turn-on and turn-off are notzero. For these reasons, by introducing the soft-switchingtechnique for the high-power system, the cost reduction,energy saving and the mitigation of environmentalproblems is largely expected.

7 References

[1] OHASHI H.: Recent power devices trend, J. IEEJ, 2002,

122, (3), pp. 168171 (in Japanese)

[2] TAKAO K., YATSUO T., A RA I K.: High di/dt switchingcharacteristics of a SiC Schottky barrier diode, IEEJ Trans.

IA, 2004, 124, (9), pp. 917923 (in Japanese)

[3] TOMASIN P.: A novel topology of zero-current-switching

voltage-source PWM inverter for high-power applications,

IEEE Trans. Power Electron., 1998, 13, (1), pp. 186193

[4] SCHONKNECHT A., DE DONCKER R.W.A.A.: Novel topology for

parallel connecion of soft-switching high-power high-

frequency inverters, IEEE Trans. Ind. Appl., 2003, 39, (2),

pp. 550555

[5] LI Y.P., LEE F.C., BOROYEVICH D.: IGBT device applicationaspects for 50 kW zero-current-transition inverters, IEEE

Trans. Ind. Appl., 2004, 40, (4), pp. 10391048

[6] BODUR H., BAKAN A.F.: An improved ZCT-PWM DC-DC

converter for high-power and frequency applications, IEEE

Trans. Ind. Electron., 2004, 51, (1), pp. 8995

[7] PENG F.Z., LI H., SU G., LAWLER J.S.: New ZVS bidirectional

DCDC converter for fuel cell and battery application,

IEEE Trans. Power Electron., 2004, 19, (1), pp. 5465

[8] HAN B.M., MOON S.I.: Static reactive-power compensatorusing soft-switching current-source inverter, IEEE Trans.

Ind. Electron., 2001, 48, (60), pp. 11581165



www.ietdl.org


10/10

[9] HAN B., MOON S., PARK J., KARADY G.: Static synchronous

compensator using thyristor PWM current source inverter,

IEEE Trans. Power Deliv., 2000, 15, (4), pp. 1285 1290

[10] ISHIKAWA H., MURAI Y.: A novel soft-switched PWM

current source inverter with voltage clamped circuit, IEEE

Trans. Power Electron., 2000, 15, (6), pp. 10811087

[11] SUZUKI H., NAKAJIMA T., IZUMI K., SUGIMOTO S., MINO Y., ABE H.:

Development and testing of prototype models for a

high-performance 300 MW self-commutated AC/DCconverter, IEEE Trans. Power Deliv., 1997, 12, ( 4) ,

pp. 15891597

[12] HE X., CHEN A., WU H., DENG Y., ZHAO R.: Simple passive

lossless snubber for high-power multilevel inverters, IEEE

Trans. Ind. Electron., 2006, 53, (3), pp. 727735

8 Appendix

8.1 GTO model (Figs. 3 and 10)

8.1.1 Derivations of switching losses in hardswitching: Switching-loss at turn-on duration: As can beseen from Fig. 10, the current and voltage equations ofGTO device at turn-on duration can be expressed as

ic VoffLon

(t Ton) : (Ton , t, Ton Tir) (11)

From (11), the equation of switching loss at turn-on durationcan be derived as

won TonTir

Ton

icvce dtVrms

2 Tir2

2Lon(12)

where Tir (LonIdc)=Vrms:

Switching-loss at turn-off duration: As can be seen fromFig. 10, the tail-current equations of GTO device at turn-off duration

ice

Idc 1 0:9t

ToffTf

!: (Toff , t, Toff Tf)

Idc10

1 t (Toff Tf)

Tt

: (Toff Tf, t, Toff Tf Tt)

8>>>>>>>>>>>>>>>>>>>:

(13)

can be expressed. From (13), the equation of switching loss atturn-off duration can be derived as

woff ToffTfTt

Tofficvce dt

1

20 VrmsIdc 11Tf Tt

(14)

Conduction-loss: The conducting-period in periodical time ofoutput-current is 1208, then AC current on 1208 conductionmode is shown in (15)

imc 2ffiffiffi

3p

pIdc sinvt

sin5vt

5 sin7vt

7 sin11vt

11

sin13vt

13 sin17vt

17 sin19vt

19 (15)

From (15), the conduction-loss equation in 1 s interval isshown in (16)

Pcon2

T

T=20

imcvce dt

w2Idcp2

3RonIdc 11

52 1

72 1

112 1

132 1

172 1

192

ffiffiffi3p Vf 2 152 172 1112 1132 1172 1192 (16)

Figure 10 Turn-on and off characteristics of GTO



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