9. IEEE Base Paper

8/18/2019 9. IEEE Base Paper

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The 6th International Power Electronics Drive Systems and Technologies Conference (PEDSTC205)

3-4 Februar 2015, Shahid Beheshti Universit, Tehran, Iran

Application of a New High Step-up Double-Input

Converter in a Novel Module- Integrated-Inverter

Photovoltaic SystemM. Mohammad N. aar J Mmonard J . Moghan

Dparmn o ra ngnrng Amrkabr nrs o hnoog

hran ran

ma: [email protected]

Abstract-Gidonneed phoovoli (GPV) uing moduleinegedinvee i well known mehod o ue PV in powenewok. Thi ppe popoe novel uue of moduleineged GPV ed on doule inpu DCDC onvee. Speil

uue nd wihing egy of he popoed onvee hgh f g f The popoed uue of moduleineged GPV ue DulPV module(DPVM) onin wo PV. DPVM i onneed ohe popoed onvee nd he oupu of he onvee ionneed o he invee. Two inpu of he onvee ih f hg hgh ondiioning GPV. The popoed DPVM i peened nd heppliion of high ep up muliinpu onvee in DPVM idiued. high epup piliy of he popoed onveei vlided y mhemil elion. Expeimenl eule peened o evlue he heii of he popoedonvee.

x rs-Gidonneed PV,high epup onvee,douleinpu onvee, o wihing, nonioled onvee.

NTODUTION

Photovoltaics has become more interesting in recent yearsdue to their clean power generation by the sunlight. As PV smass production cost has been decreased cost reduction of

power conditioning systems used in GPVs needs to happen. Due to low DC voltage generated by PVs a power conditioning system is required to connect PV to the power network[1]. GPV systems include four categories which are listed asfollows:

1) Central inverter GP

) String inverter GP3) Multistring inverter GP4) Moduleintegratedinverter GPV(AC module).

Centralized inverters [, [2 which are shown in gaconnect a large number of PVs to the power network. Inthis GPV conguration, PV odules are connected in se

ries that is called a string to achieve a high voltage forcentral inverter String diodes are used in this conguration

to connect string PV s in parallel and achieve high powerstructure. Due to central maximum power point tracker usedin this conguration, ptia shadow and axiu power

point isatches, reduction of efciency occurs Also, ass

production of this conguration is not possible [ In string

97-1-4799-7653-9/15/$31.00 ©015 I 53

inverter GPV [3] each string is connected to the network usinga separate inverter (g b) As a result, the partial shadow

eect decreases and efciency of GPV considerably increases

To achieve a high voltage DC link at the input side of theinverter 16 PVs are connected in seriesin Europe) which results a voltage up to 2V at the input terminal of theinverter; So a high voltage power switch is required []. Inorder to decrease the maximum voltage of DClink it is possible to use a multistring inverter GPV (Fig.c). In thisconguration lower nuber of PV s are utilized and the voltage

is boosted by a DCDC converter [4]. considering the use ofa central inverter both former methods result in lower mass production cost and lower mismatch losses of the PV modules.Moduleintegratedinverter GPVs [] are the last type of GPVsystems in which a PV module with a power conditioningsyste(aplication and conversion to AC) creates a odue

integratedinverter GPV(MII-GPV) (g d) Due to the low

generated voltage of PV modules MIIGPVs require a high voltage aplication which decreases the eciency of te

system. But low cost of mass production of this type of GPVscauses the manufacturers to be interested in this ind of GPVs.

High stepup DCDC converters [6] are good choices tobe used in tis application to increase the efciency of te

converter by operating in a low duty cycle and so switchingcondition [] [8]; however the use of so switching high stepup converters is not an optimal solution for achieving higheciency perforance The ain eod for soft switchingoperation in these converters is to insert lag cuent into

power switches; but this results in increasing the magneticlosses of the converter also turning o switching losses areincreased due to extra magnetic cuent that is required forso switching. Overall the so switching operation that isachieved by tis ethod, increases the efciency of converter

with respect to hard switching operation. To achieve higherefciency in high gain DCDC converters, it is required to

use new methods to achieve so switching condition withoutincreasing magnetic current.

In this paper a novel moduleintegratedinverter GPV structure is proposed based on doubleinput DCDC converters [].In this topology which is shown in Fig. a couple of PV

modules are used as a DualPVModule (DPVM). So two


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String Inverter Based Gridconected-PV

PVn PVn

Central CentralInverter Inverter

3phase

b

Multi-String Inverter BasedGrid connected-PV

DC-DC DC-DCConverter Converter

CentralInverter

3phase

c

cOlmectedPV

d

Fig. 1: Different types of grid connected PVs

PV terminals exist in a single DPVM and it is possible touse a doubleinput high gain DCDC converter to amplifyPV modules to an appropriate value for gridconnected in verter. The aim of using doubleinput DCDC converter inthe proposed structure is to achieve higher reliability highereciency and inexpensive MIIGP Unlike High stepup DC

DC converters which use an extra cuent to achieve so

switching operation in the proposed structure a doubleinputconverter is used to provide so switching condition based onswitching techniques; as a result turningon switching lossesis omitted without using extra current so total losses of theconverter decreases further with respect to high step up soswitching DCDC converters in literature.

The proposed converter is shown in Fig.3. The convertercontains a threeswitch cell a boosting transformer and a voltage mUltiplier. As the switching strategy leads to soswitching operation in the converter no transformer branchis required to guarantee so switching operation. Therebyitis possible for the converter to operate in under resonance

frequency and large magnetizing inductance of the transformerand consequently the conducting losses of the converter will be alleviated. Moreover operation of the converter in under resonance frequency helps to operate in high switchingfrequency and the value of multiplier's capacitors becomessall subsequently, the converter size decreases sufciently

In section II the proposed converter is analyzed and itsoperation intervals are discussed. voltage gain of the converteris derived in section III and compared in dierent valuesof transformer tu ratio. A design example is presented insection IV. The experimental results of the proposed converterare shown and analyzed in section V to validate the proposed

converter performance.

54

V V

1--

.

-- T Gower Conditioner

Fig. : Basic structure of proposed ModuleIntegratedPV

---------------------------

1 :

ulti·rt Cll ltag Amplifr cllFig. 3: Proposed double input converter


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II. OOED OOLOY

In this section the proposed converter are discussed analyzed and different modes of operation of the converter is presented. Fig.3 illustrates a detailed view of the proposedconverter. According to this gure the converter contains two

main parts. First is a double input cell that two inputs areconnected to this cell. This part contains three switches andtwo inductors that are used to reduce ripple of PV sources.The switching strategy of the converter is Pulse width modulation(PWM) with a special structure. Fig. shows the keywaveforms of the converter in double input operation mode.According to this gure, switches and are tued onsimultaneously. During this switching strategy the current ofinductor L ows trough body diode of and . Alsoaccording to connection of capacitor to the Switch so switching of this switch is guaranteed due to AlternativeCurrent(AC) of capacitors in steady state condition. These

result in Zero Voltage Switching ( ZVS) of the switches in

double input mode. Second part of the converter is voltageamplier cell. This part contains a boosting tansformer and a voltage multiplier. Voltage multiplier increases voltage gain ofthe converter by three times that results in lower turns ratio ofthe transformer and as a result lower current stress of switchesof the multi input cell.

The converter operates in six intervals which are discussedhere. Before analyzing the converter's operation modes following assumptions are considered:

All switches and diodes are ideal. Inductors and capacitors are ideal. Voltage of and have no ripple.

Interval 1 : [ This interval starts when and areturned on simultaneously. Switch is off in this interval.Inductor L charges and L discharges into capacitor . During this interval diode is on and the power of load issupplied by PV sources. Due to low value of the cuent ofsecondary side of the boosting transfoer varies sinusoidallywith the frequency of � 0 and at the end of this interval

L'"diode tus o and s interval nishes.

Interval : [ This interval starts when diode turnsoff. During this interval the state of switches remains constantand no power is transfered to the output. In this interval theoutput power is supplied by and the voltage of remains

constant. still charges . at the end of this interval isturned off.

Interval 3: This interval occurs fast that during it thecuent at ew through switch charges drainsourcecapacitor() of and discharges of . when the voltage of switch reaches zero value body diode of thisswitch starts to conduct and now the cuent ows through body diode of switch . Due to AC cuent of capacitor this phenomena occurs certainly. As a result Switch always is turned on inZVS condition.

Interval 4: [ At start of this interval switch isturned on in zerovoltage condition. During this interval

both switches and are on and input inductors store

55

D I I

•

I

�_____�___-

_

w

_

_

f+

I

I I t( t2

II

t4 t;

t� t7

Fig. : Key waveforms of the proposed converter

energy. still is o and supplies the load but thecurrent of secondary side of the transformer( ) is not zeroand charges . In this interval both diodes and operate similarly. The cuent varies sinusoidally with thefrequency of

2

7

' According to intervals 1 and 4 theconverter operates in two resonant condition. So the cuent of

multiplier diodes vary more linear. this phenomena is helpful because switch is turned o in the next interval when thesesdiodes are on. so to have lower tuo switching losses itis desirable to operate with smaller current. As a result the best operating point of the converter could be the resonantfrequency of L (

2

7

)

because at this switchingfrequency output diode operates in under resonant frequencyand mUltiplier diodes operate in aboveresonant frequency.Interval nishes when the switch is turned off.

Interva: [ At start of this interval switch is tuedoff and the inductor L charges This interval nishes whenthe current reaches zero. So at the end of this interval

diodes and tu off.


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5

i=Voltage gain for n=230 ....... Volta ge a in f or n=3

oltag gain or n=425 ... .. Convntonal boost

20

5

0.4 5 Duty ycl D 1

Fig. 6: Voltage gain of proposed converter with respect to dutycycle Dl for various values of n

8) If the connection of output side of the transfoer is reversed then the voltage gain is calculated according toabove steps as follows:

M 2 =(Vc; -V2)

V I()

To achieve the optimized voltage gain the connection of thesecondary side of the transformer is deteined according tothe ratio of V2 divided by V I is grater than M2 if thefollowing condition exists:

(1)

Fig.6 shows the voltage gain of proposed converter with respect to duty cycle Dl for various values of turns ratio n.According to this gure, using a smal value of tus ratio

of the transformer it is possible to achieve high voltage gainand reach 00V for connecting to DC link. According to thisgure as the tus ratio is increased the required duty cycle

for reaching 00V decreases.

IV. EIN XAMLE

This section presents a design example of the converter

which its characteristics is as follows:

input voltage V I: 30-0V input voltage V2: 35-0V output voltage V : 00V output power P o: 00 ripple of output voltage �V : V Switching frequency : Hz

A Power Semiondutors

According to duty cycle of the switches and the value of

input sources voltage of Vc is no larger than 1 volts. Also

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the maximum value of switches' cuent is that one of switch as follows:

se of (11) results in maximum current of switches equalto 1A So the switch IXFC6N1P of IXYS company isselected for power switches. According to maximum voltageand current of the output diodes which are equal to 310Vand respectively ultrafast diode R460 is selectedfor output diodes.

B Passive omponents

To select the input inductors the ripple of input current ofthe converter which is presented below is used.

�

l =V IDIT

(1)Ll

� 2 =V2D2T

(13)L 2

According to (1) and (13) for achieving a ripple equal to 2Afor the inputs Ll and L2 are designed for 130H and 10H respectively. According to g.6 the tansformer tus ratio is

selected as = .3 to achieve the required voltage gain.Capacitor 0 has the maximum voltage equal to 0V and forachieving voltage ripple equal less than V a polystere .7Fis selected. Due to the leakage inductance of the transformerwhich is equal to 0H the required value of

Okis equal

to 70 So the maximum voltage across Ok is equal to130V and a 1 volts polystere capacitor is chosen. The outputcapacitor is selected as F to achieve an output voltage withless than V voltage ripple.

V. XEIMENTAL REULT

To validate the characteristics of the proposed converter itwas proto typed in laboratory. In this section the Experimental

results is presented and discussed. The main goal of this prototype is to show so switching operation of the proposedconverter in double input operation mode. To show the so

switching condition voltage of gatesource and drainsourcear sown in gs.7a, 7c an 7. As t cunt 2 owsthrough body diode of and before they are tued onthese switches operate in zero voltage switching conditionclearly. According to gs.b, d and f which show te

current of switches all the currents are negative when thegatesource voltage is applied to switches. Fig.g shows the primary current of the tansformer and g.h illustrates te

cuent of leakage inductance of the transfoer. This gure

shows the resonant operation of the converter. Figs.i and jare presented to show the zero cuent switching operationof outut diodes. The efciency of proposed converter was

calculated as 6.4% for 00 output load.


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Tek J • Stop.

n l

. ,

"

UV "

CH1 .00/ C2 00 20us

(a )

Cl 00\ C 00 0)�

(e)

P: 0,0005

Tek J eSo MPo;:-300Ons.

2�

b

00 00A

f

Tek eSo MPO00 Tek eSo MPos 300O. VOS2 D

c

'

,

Jc

C 0 C2 00 00

g

t

�

C 0( C"O M OOw

d

:

,.

5 �OV

CH2 00 M 00

hTek eSo MPo; 3000 Tek eSo

M P -3000

,J 00 00 M OO

i 00 +O M 00)

Fig. 7 Experimental results. (a) VDS and V of switch (b) V and D of switch (c) VDS and V of switch (d)

Vand

Dof switch (e)

VDSand

Vof switch

Vand

Dof switch (g)

Vof switch and primary

side current of the transformer (h) secondary side voltage and current of the transformer (i) cathodeanode voltage and anodecuent of the mUltiplier diodes ) cathodeanode voltage and anode current of the output diode.

VI. ONLUION

This article proposed a novel moduleintegratedbased GPVusing a new high gain double input DCDC converter with soswitching for microgrids applications. the proposed converterused a low voltage DClink to connect PVs to each other andused them to achieve so switching operation without usingextra inductive cuents. To achieve high voltage gain by use oflow tus ratio of the boosting transformer a voltage mUltiplierwhich increases the voltage gain three times was used that itsdiodes operated in zero cuent switching condition due toleakage inductance of the transformer. The characteristics ofthe proposed converter was validated by experimental results.

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9. IEEE Base Paper