Tài liệu tiếng anh Điện tử công suất mạch MERS Loss and rating consideration of a wind energy conversion system with reactive compensation by magnetic energy recovery switch

Luận văn, Điện tử công suất, đề tài tốt nghiệp, đồ án, thực tập tốt nghiệp, đề tài

Loss and Rating Considerations of a Wind Energy

*Norwegian University of Science and Technology (NTNU)

+Fuji Electric Device Technology Co., Ltd.

Keywords

<<Converter circuit> >,< <Generator excitationsystem»>, <<Powerfactorcorrection»>

Abstract

Electrical conversion system for permanent magnet wind generators is challenging due to the large rating

of power electronics devices needed and the associated costs Additionally, due to the large inductance

in-vestigated MERS is asimpleconfiguration with low switching losses Due to the special characteristics

configurationhas been confirmed with experiments on a 50 kW multi-pole permanent magnet generator

comparedtousingaconventional active rectifier solution

Introduction

Multi-pole permanent magnet (PM) generators represent one of the promising technologies for wind

challenge is, however, the efficient conversion of the generator electrical currents to suitable ac voltage

1j-1X114 ERS X 3 1

Discharging Parallel by-pass Charging

Figure2: Control ofcurrentpath throughMERS whencurrentis goingfromlefttoright.

0

co

0~

0 -0~~~~~~~~~~~~~~~~~X~~~~~~~~~ 'o U \ I*t1 U _,I.

Figure 3: Example voltage andcurrentwaveforms withtwodifferent modes ofoperation

needed, representing amajorcostand loss component Another issue is the size of the generator which

the generator to the maximum in order to avoid unnecessary additions to the generator dimensions and costs

canprovidethe necessary reactive power to utilize the powercapabilityof the generator to themaximum, however,this comes with additional power electronics devicerating requirements and also resulting high losses and costs

A configuration using avariable series compensation device called a magnetic energy recovery switch

recti-fier [1] [2] This paper studies the loss andrating considerations of this solution further First,the basics

PM generatorand theoretical large scale system loss and rating investigations

Configuration and operation

Synchronous generator um E

I Ra XSi ~~~~~~~~~~~~~/XL XSI/L

/L~~~~~~~~~~~~~~~~~~~~~~~~'

Figure 4: Illustration of electrical conversionconceptwithphasor diagrams (b) Phasor when notusing MERS,

generatorvoltage drops and output powerislimited (c) Phasor whenusing MERS Thevoltage acrossthe

syn-chronous reactance canbecancelled andoutput powerincreased

de-vice(Fig 2) Examples ofresulting curves are shown inFig 3 Two modes ofoperationare indicated,

thecontrol, the MERS can act as a variablecapacitor The size of thecapacitive injectedseries voltage

switching and also softswitching The device will always turn-on at zero currentand in not continous

switching losses and on-state voltage With most applications requiring high switchingfrequencies and hard switching capability, the switching losses are normally prioritized With effort in reducing the

Application to wind power system

The suggested conversion system usingMERS for wind power converison is shown in Fig l(b) The

voltage drop across the synchronous reactance,Xs. Without anycompensation, the output voltagewill

Experiments

on a multi-pole 50 kW PM generator designed in the image ofa wind power generator A picture of theexperimental set-upis shown inFig 5 An induction generator drives aslowrotating PMgenerator

through agear-box Thegeneator outputis connectedtotheMERS,adiodebridgeand then fed into the

Experimentswereconductedby manually applyingvariousdegreesofcompensationand variousgrid

in-verterdc-linkvoltages The results whenkeepingthe generatorfrequencyconstant areshown inFig 6(a).

Byreducing the dc-linkvoltage, the power output can be increasedto a certain level Additionally, the

distortion in the generator terminal voltage; however, the distortion in the current is significanlty lower

The meausred and estimated losses for the whole power operating range with 50 Hz operation and

compared to the use of traditional switches The total MERS and diode bridge losses are close 2.9 %, which is high compared to conventional large scale systems The high losses are mainly due to the low voltage utilization of the semiconductor devices and indicates the need for large scale loss and rating

esimtations

Gheneator Ratedpower 50 kW

No-loadvoltage 306 V

Synid onous ind :tance 4.5Cm4H

MERS convertor: ~~IGBTcurrentrating 150A

Figure 5: Picture ofexperimental set-up Induction motor is driving a multi-pole 50kW PM through a gear.

Generatoroutputis connectedtoMERSsystemand then thegrid side inverter

TableI:Designparametersused forlarge scalesysteminvestigations

Rating and loss considerations for large scale system

is suggested for the MERS IGBTs comparedto the active rectifier due to smallervoltage over-shoot at

design wasbased on +/- 10 % variable speed operation with rated current This was selected, such that

phase voltage Forthe MERS case, the maximum series injected voltagewasidentifiedbysimulation to

multiplyingthe devicesupply voltageand the number ofswitches,the relativesupply ratingresults The

value indicates that withequal voltage utilization of the switches and equal lossperswitch, the rating of

peak junction temperature of 125°C and 80°C heat sink temperature has been assumed Over-current

capability of 25% has also been included The results of the loss evaluation are shown in Fig 8(a)

simplified calculations using high modulation index, third harmonic injection PWM and two different

and voltage, the on-state losses are mainly from the diodes This means that the temperature in the diodes is the main limitation for current capability of one IGBT device Decision of optimial switching frequency is a complex consideration mainly related to the filter design, cost and losses and has not been

1%[4][5] The losses of the MERS system are significantly lower than that for the active rectifier system Relative rating need has been defined as the voltage rating times current rating of the IGBT times number

of switches divided by the generator output power The resulting relative rating need of the semicondutor

>500 - y,/Generatorside, RS

A Vdc=355V * Vdc=385V C Capa,

o-,-* Vdc=370V * Vdc=400V 4 0 -' -

p ,rDc-voltage -500 Diodeside, RS]<

100 040

0~~0

MERS set-point, 6 (deg.) time (s)

Figure 6: (a) Control of output power by adjusting MERS set-point or the grid inverter dc-link voltage (b) Resultingcurveswhen operatingat39 kWgenerator output powerand355Vdc-link voltage

to be only 24 % higher for the active rectifier, difference in voltage utilization, switching losses and low on-state IGBTs results in the actual needed rating being significantly higher than that for the MERS

Conclusion

simple control and low switching losses, the size of the capacitive injected voltage can be controlled

Experiments on a 50 kW machine demonstrates and verifies the performance of the suggested system

implementationofefficient,compactand cost effective electrical conversion for permanent magnet wind

generation

References

[1] T.Takaku,G Homma, S.Igarashi,Y Uchida,and R Shimada Power up andefficiency improvement

2006, 2006

Marta Molinas, and Tore M Undeland A new ac current switch called mers with low on-state

[4] Xiangjun Zeng, Zhe Chen, and Frede Blaabjerg Design and comparison of full-size converters for large variable-speed wind turbines EPE, 2008

[5] BjomnAndresen and Jens Birk A high power density converter system for the gamesa glOx 4,5 mw wind turbine EPE, 2008

>~150- - Estimated 150 New Ne IB IGBT

o1000 Measured 'NormalIGBT

11001-c10

L

C-0~~~~~~~~~~~~~~

MERS IGBTs , 150

' 1 : +Diode - bridge -Normal Diode

o MERS, measured ,,' - 100 /

aB L 1 O050

-CDC

Generator output power (kW) On-state voltage, terminal (V)

Figure7: (a)Loss measurementand estimation ofMERS system and diode bridge withcancellationoffull voltage drop across synchronous reactance. (b) Measured characteristics of low on-state voltage IGBT compared to a

conventional IGBT

29.8 VA/W

1.14%

22.7 VA/W 0.86%

Figure8LagscllosadrtncosdrtosfrMRadactierciirsses.()Ls smtos~ Cn

CbRtndg esimtons.

(-22%)~ ~ ~ ~~~~Emmmmm

EmmmmmmmmNrml ow 1kz kH NormalLow I kHz 2 kHz kHzmmmmmmm 3 EmmmmmmmmmIGT O-Sat

IGBT On-State~~~~~~~~Emmmmm

(a) (b)mmmm

Figure 8: Large scl os n ain osdeain orMR ndatv rciirsytm.(a osesmtos

(b)Ratingestimations.~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~