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This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication. Citation information: DOI10.1109/TPEL.2015.2469658, IEEE Transactions on Power Electronics

Transformerless Single-Phase Universal ActiveFilter with UPS Features and Reduced Number of

Electronic Power SwitchesW. R. N. Santos, E. M. Fernandes, E. R. C. da Silva, C. B. Jacobina, A. C. Oliveira and P. M. Santos

Federal University of Piauı - UFPIFederal University of Campina Grande - UFCG

Federal University of Maranhao - UFMAemail: [email protected] andeisenhawer, edison, jacobina, [email protected] and [email protected]

Abstract-This paper presents an universal active powerfilter for harmonic and reactive power compensationwith UPS (Uninterrupted Power Supplies) features. Theconfigurations does not use transformer in the series part.Transformerless modern UPS systems have been rapidlyreplacing the old technology due to their performance andsize attributes. Reducing the numbers of passive elementsand/or switches in active power filters and UPS topologiesnot only reduces the cost of the whole system but alsoprovides some advantages, such as great compactness,smaller weight, and higher reliability. However, the costreduction requires the use of more complex control strate-gies. The model of the proposed system is derived andit is observed that the system can be reconfigurable tooperate with four or three-leg depending on the issue. Acomplete control system, including the PWM (Pulse-WidthModulation) techniques, is developed and a comparisonbetween the proposed filter and the standard one is done,as well. Simulated and experimental results validate thetheoretical considerations.

Keywords –universal active power filter, single-phasestructure, uninterrupted power supplies and PWM tech-niques.

I. I NTRODUCTION

The requirements of quality at power grids and increasedsensitivity of the loads has stimulated the use of powerelectronics in context of power line conditioning [1]. Differentequipments are used to improve the power quality, e.g.,transient suppressors, line voltage regulators, uninterruptedpower supplies, active filters, and hybrid filters [1], [2], [3], [4],[5], [6]. The continuous proliferation of electronic equipmentseither for home appliance or industrial use has the drawbackof increasing the non-sinusoidal current into power grid.So, the need for economical power conditioners for single-phase systems is growing rapidly [2], [7], [8], [9], [10], [11].Different solutions are currently proposed and used in practiceapplications to work out the problems of harmonics in electricgrids. In the last decades, the use of active filtering techniqueshas became more attractive due to the technological progress in

power electronic switching devices and more efficient controlalgorithms.

The issue of reducing the cost has been attracting theattentions of researchers. Generally, the largest cost reductionis achieved by reducing the number of switches employed inpower converter or developing topologies that employ switcheswith lower voltage stresses. Cost reduction is also achieved byeliminating passive components such as inductors, capacitorsand transformers. Reducing the numbers of switches andpassive elements in Active Power Filters (APF) and Unin-terrupted Power Supplies (UPS) topologies not only reducesthe cost of the whole system but also provides some otheradvantages such as great compactness, smaller weight, andhigher reliability [12], [13], [14], [15], [16], [17]. However,the cost reduction requires the use of more complex controlstrategies.

Uninterrupted power supplies are widely used to supplycritical loads and provide reliable and high quality energytothe load [15], [18], [19], [20]. Static UPS systems are the mostcommonly used UPS systems. They have a broad variety ofapplications from low-power personal computer and telecom-munication systems, to medium-power medical systems, andto high-power utility systems. The main advantages are highefficiency, high reliability, and low THD (Total HarmonicDistortion). The static UPS systems are classified into on-line,off-line and line-interactive.

This work will focus on the study of series-parallel line-interactive UPS topology, also known as delta converter, withreduced number of switches. The idea consists in developinga reconfigurable structure where one of the converter-legcan be used to charge the battery bank without having adedicated d.c./d.c. converter, e.g., buck-boost converter. So,the configuration composed by four-leg converter can operateswith three-leg leaving one leg to charge the battery bank. Whenthe battery bank is charged, the system returns to its originalform. A mathematical modelling and complete control system,including thePWM techniques, is presented. Simulated andexperimental results validate the theoretical considerations.

II. SYSTEMS MODELLING

The proposed configuration shown in Fig. 1 (a) comprisethe grid (eg, ig), internal grid inductance (Lg), loadZl (vl, il),



(a) (b)

Fig. 1. Single-phase universal active filter topologies with UPS features. Proposed (a) and conventional (b).

convertersSe andSh with a capacitor bank at the d.c.-link andfiltersZe (Le, L′

e andCe) andZh (Lh, L′

h andCh). ConverterSe is composed by switchesqe, qe, q

′

e and q′e. ConverterSh

is composed by switchesqh, qh, q′h and q′h. The conductionstate of all switches is represented by an homonymous binaryvariable, whereq=1 indicates a closed switch whileq=0 anopen one.

The difference between the two systems, Fig. 1, relates tocomponents reduction. The proposed configurations, Fig. 1 (a),is transformerless and presents less power switches than theconventional, Fig. 1 (b). The idea of the proposed system isto utilize one of the converter-leg to charge the battery bank -when d.c. voltage level at the battery bank is beyond the presettolerance - avoiding the necessity to have a dedicated d.c./d.c.buck-boost converter for it. The buck-boost converter of theconventional topology is composed by switchesqb1 and qb2.The filter inductanceLcc is common to both configurations.The system description with the power converter operatingwith four and three-leg is addressed.

A. Four-leg converter operation mode

The converter pole voltagesve0, v′e0, vh0 and v′h0 dependon the conduction states of the power switches, that is

ve0 =(2qe − 1)vc2

(1)

v′e0 =(2q′e − 1)vc2

(2)

vh0 =(2qh − 1)vc2

(3)

v′h0 =(2q′h − 1)vc2

(4)

wherevc is the d.c.-link voltage.

From Fig. 1(a), assuming that the switchesS1 andS2 are onandS3 andS4 are off, the following equations can be derivedconsidering the system operating with four-leg:

ve0−v′e0 = vg+

[

r′e2+re2+

(

le2+l′e2

)

p

]

ie−vl−

(

r′e2+l′e2p

)

io(5)

vh0−v′h0 =

[

rh2+r′h2+

(

lh2+l′h2

)

p

]

ih+vl+

(

r′h2+l′h2p

)

io(6)

v′e0−v′h0=−

(

r′e2+l′e2p

)

ie+

(

r′h2+l′h2p

)

ih + vl

+

[(

r′e2

+r′h2

)

+

(

l′e2+

l′h2

)

p

]

io (7)

ve0−vh0= vg−vl +

(

re2+le2p

)

ie−

(

rh2+lh2p

)

ih (8)

eg − vce − vl =(rg + lgp) ig (9)

pvce=1

Ce

(ig + ie) (10)

pvl =1

Ch

(ig − il + ih + io) (11)

where p = d/dt, vg = eg − rgig − lgpig, vl = vch and ilis calculated using the load model which can be linear ornonlinear; and symbols liker and l represent resistances andinductances of the inductorsLg, Le, L′

e, Lh and L′

h. Thecirculating currentio is defined by

io = ie + i′

e = −(ih + i′

h) (12)

The resultant circulating voltage model is obtained by



adding (5)-(8):

vo = v′e0 + ve0 − v′h0 − vh0

vg+

[(

r′e2+r′h2

)

+

(

l′e2+l′h2

)

p

]

io

+

[(

re2

−r′e2

)

+

(

le2−l′e2

)

p

]

ie

−

[(

rh2−r′h2

)

+

(

lh2−l′h2

)

p

]

ih (13)

The voltagevo is used to compensate the circulating currentio. The demonstration of this current can be seen in appendixof [16].

From the point of view of the controllers, the voltages:ve=ve0 − v′e0 (converterSe) is used to regulate and compensatethe load voltagevl, vh = vh0 − v′h0 (converterSh) regulatesand controls the grid current in order to maintain the powerfactor close to one andvo = v′e0 + ve0 − v′h0 − vh0 (converterSe +Sh) is used to cancel or gather the circulating currentionear to zero.

In the balanced case, filter inductors are equal (Le = L′

e

andLh = L′

h) and the circulating voltage model become moresimple, that is,

vo=vg+

[

(re2

+rh2

)

+

(

le2+

lh2

)

p

]

io (14)

Thus, it can be noted that to minimize the circulating currentio, the voltagevo must be equal tovg, i.e.

vo = vg (15)

When io = 0 (ie = −i′

e, ih = −i′

h) the system modelbecomes:

ve0−v′e0 = vg+(re+lep)ie−vl (16)

vh0−v′h0=(rh+lhp)ih+vl (17)

eg−vce−vl =(rg+lgp)ig (18)

pvce=1

Ce

(ig+ie) (19)

pvl =1

Ch

(ig−il+ih) (20)

This model is quite similar to the model of the conventionalfilter with an ideal transformer. Therefore, we can useve =ve0 − v′e0 (converterSe) to regulate the load voltage andvh=vh0−v′h0 (converterSh) to control the power factor andharmonics ofig as in the conventional filter.

B. Three-leg converter operation mode

The system composed by three-leg works similar but, inthis case, it has a shared-leg used by both converters (seriesand parallel filter) and a free-leg which is used to charge thebattery bank when needed. The converter pole voltagesv′e0,vh0 and v′h0 depend on the conduction states of the powerswitches and may be expressed as

v′e0 =(2q′e−1)vc2

(21)

ve0 =(2qe−1)vc2

(22)

v′h0 =(2q′h−1)vc2

(23)

Assuming that the system operates with three-legs, consid-ering the switchesS1 andS3 are on andS2 andS4 are off,can write the following equations:

ve0−v′e0 = vg−vl +

(

re2

+le2p

)

ie−

(

r′e2+l′e2p

)

i′e (24)

v′e0−v′h0 = vl+

(

r′e2+l′e2p

)

i′e−

(

r′h2+l′h2p

)

i′h (25)

ve0−v′h0= vg+

(

re2+le2p

)

ie−

(

r′h2+l′h2p

)

i′h (26)

eg−vce−vl =(rg + lgp)ig (27)

pvce =1

Ce

(ig+ie) (28)

pvl =1

Ch

(ig−il) (29)

where p = d/dt, vg = eg − rgig − lgpig, vl = vch and ilis calculated using the load model which can be linear ornonlinear. For this case, it is noted by the equations that thereis no circulation currentio.

III. PWM STRATEGY

This section presents thePWM Strategy for differentmodes of operations. Firstly, the system starts as four-legconverter and when is need to charge the bank of batteriesit is reconfigurable to operate as three-leg. The descriptions ofthese modes of operations are presented as following.

A. Four-leg converter operation mode

Pulse-widths of gating signals can be directly calculatedfrom the pole voltagesv∗′e0, v∗e0, v∗′h0 andv∗h0.

Considering thatv∗e , v∗h and v∗o denote the referencevoltages requested by the controllers (see Section IV), it comes

v∗e0 − v∗′e0 = v∗e (30)

v∗h0 − v∗′h0 = v∗h (31)

v∗′e0 + v∗e0 − v∗′h0 − v∗h0 = v∗o . (32)

Such equations are sufficient to determine the four pole volt-agesv∗e0, v∗′e0, v∗h0, andv∗′h0. Introducing an auxiliary variablev∗x and choosingv∗′e0 = v∗x, it can be written

v∗e0 = v∗e + v∗x (33)

v∗′e0 = v∗x (34)

v∗h0 =v∗e2

+v∗h2

−v∗o2

+ v∗x (35)



v∗′h0 =v∗e2

−v∗h2

−v∗o2

+ v∗x (36)

Two methods are presented in order to choosev∗x.Method A: General approachIn this approach, the reference voltagev∗x is calculated by

taking into account the maximumv∗c/2 and minimum−v∗c/2value of the pole voltages, then:

v∗xmax= v∗c/2−v∗

max(37)

v∗xmin=−v∗c/2−v∗min (38)

wherev∗c is the reference d.c.-link voltages,v∗max

= maxϑ andv∗min

= minϑ with ϑ = v∗e , 0, v∗

e/2 + v∗h/2 − v∗o/2, v∗

e/2 −v∗h/2− v∗o/2.

After v∗x is selected, all pole voltages are obtained from(33)-(36). Then,v∗x can be chosen equal tov∗xmax

, v∗xminor

v∗xave= (v∗xmax+v∗xmin

)/2. Note that whenv∗xmaxor v∗xmin

isselected, one of the converter-leg operates with zero switchingfrequency. On the other hand, operation withv∗xave generatespulse voltage centered in the sampling period that can improvethe THD of voltages.

The maximum and minimum values can be alternativelyused. For example, during the time intervalτ choosev∗x =v∗xmax

and in the next choosev∗x = v∗xmin. The interval

τ can be made equal to the sampling period (the smallestvalue) or multiple of the sampling period to reduce the averageswitching frequency.

Once v∗x is chosen, pole voltagesv∗′e0, v∗e0, v∗′h0 and v∗h0are defined from (33)-(36). Since the pole voltages have beendefined, pulse-widthsτe, τ ′e, τh andτ ′h can be calculated by:

τe =T

2+

T

vcv∗e0 (39)

τ ′e =T

2+

T

vcv∗′e0 (40)

τh =T

2+

T

vcv∗h0 (41)

τ ′h =T

2+

T

vcv∗′h0 (42)

Alternatively, the gating signals can be generated by compar-ing the pole voltage with a high frequency triangular carriersignal.

Method B: Local approachIn this case, the voltagev∗xs is calculated by taking into

account its maximum and minimum values in the series orshunt side. For example, if the series side is considered (s = e)then v∗xemax = maxϑe and v∗xemin

= minϑe with ϑe =v∗e , 0 and if the shunt side (x = h) is consideredv∗xhmax

=maxϑh and v∗xhmin

= minϑh with ϑh = v∗e/2 + v∗h/2 −v∗o/2, v

∗

e/2 − v∗h/2 − v∗o/2. Besides these voltages, voltagev∗x must also obey the other converter side. Then, these limitscan be obtained directly fromv∗xmax

andv∗xminfrom (37) and

(38).The algorithm for this case is given by:

1) Choose the converter side to be the THD optimizedand calculatev∗xs betweenv∗xsmax

, v∗xsminor v∗xsave =

(v∗xsmax + v∗xsmin)/2.

2) Calculate the limitsv∗xmaxand v∗xmin

from (37) and(38).

3) Do v∗xs = v∗xmax if v∗xs > v∗xmax and v∗xs = v∗xminif

v∗xs < v∗xmin.

4) Do v∗x = v∗xs.5) Determine the pole voltage and the gating signal as in

previous method.

B. Three-leg converter operation mode

The pulse-widths of the gating signals can be directlycalculated from the voltage referred to the d.c.-bus midpoint,which is given by the desired voltages for the grid and loads.If the desired phase voltages are specified asv∗e e v∗h then thereference midpoint voltages can be expressed as

v′e0∗

= v∗e+v∗e0 (43)

v′h0∗

= vh∗+v∗e0 (44)

Note that these equations cannot be solved unlessv∗e0 isspecified. Relations (43) and (44) can be formulated as

v′e0∗

= v∗e+v∗µ (45)

v′h0∗

= vh∗+v∗µ (46)

v∗e0 = v∗µ (47)

The problem to be solved is to determinev′e0∗, v′h0

∗ andv∗e0from (45) - (47), once the desired voltagev∗e andv∗h have beenspecified. In the following, two techniques will be presentedfor generating thePWM gating signals for the converters.

Method A: General approachThe voltagev∗µ can be calculated taking into account the

general apportioning factorµ, that is

v∗µ =E

(

µ−1

2

)

−µv∗max

+(µ−1)v∗min

(48)

where:v∗max

= max(v∗e , v∗

h, 0) andv∗min

= min(v∗e , v∗

h, 0).The apportioning factorµ (0 ≤ µ ≤ 1) is given by

µ=toito

(49)

and indicates the distribution of the general free-wheelingperiod to (period in which voltagesv′e0, vh0 and ve0 areequals) between the beginning(toi = µto) and the end(tof = (1− µ) to) of the switching period. The apportioningfactor can be changed as a function of the modulation index(µ) to reduce theTHD of both converter voltages.

In this case, the proposed algorithm is:1) Choose the general apportioning factorµ and calculate

v∗µ from (48).2) Determinev′e0

∗, v′h0∗ andv∗e0 from (45) - (47).

3) Finally, once the midpoint voltage have been determined,calculate pulse-widthsτe, τ ′e andτ ′h.

τe =T

2+

T

Ev∗e0 (50)



τ ′e =T

2+

T

Ev′e0

∗ (51)

τ ′h =T

2+

T

Ev′h0

∗ (52)

Method B: Local approachThe voltagev∗µ can be calculated taking into account the

local apportioning factorµs:

1) for the gridµs = µe, dividing (splitting) the periodtoe,in which the voltagesv′e0 andve0 are equal, at the begin-ning (toie = µetoe) and at the end(tofe = (1− µe) toe)of the switching period.

2) for the loadµs = µh, splitting the periodtoh, in whichthe voltagesv′h0 and ve0 are equal, at the beginning(toih = µhtoh) and at the end(tofh = (1− µh) toh) ofthe switching period.

Thus, the reference voltagev∗µs can be expressed by:

v∗µs =E

(

µs−1

2

)

−µsv∗

smax+(µs−1) v∗smin (53)

where v∗smax = maxVe and v∗smin= minVg if s = e or

v∗smax= maxVh andv∗smin

= minVh if s = h, whereVe =v∗e , 0 andVh = v∗h, 0. Besides (53), the voltagev∗µs mustalso obey the other converter side. Then, from (45) and (46)the limits for v∗µs can be calculated

for s = e :

v∗µsmax=

E

2−v∗h (54)

v∗µsmin=−

E

2−v∗h (55)

for s = h :

v∗µsmax=

E

2−v∗e (56)

v∗µsmin=−

E

2−v∗e (57)

In this case, it is possible to control how the harmonicdistortion is divided by both converters. So, the proposedalgorithm is:

1) Choose the local apportioning factorµs so that grid orload converter is optimized, calculatev∗µs from (48).

2) Determinev′e0∗, v′h0

∗ and v∗e0 from (45) - (47) usingv∗µ = v∗µs.

3) Use Step 3 of Method A.

IV. OVERALL CONTROL STRATEGY

As mentioned in the previous sections, the modes of oper-ation of the converter is defined by the system functionality.The system can operate with four or three-leg depend on theneed; or in case of grid voltage fault, the battery bank is usedto supply energy to the d.c.-bus capacitor voltage and inverterin order to maintain the desirable voltage to the load.

The description of the operation mode of the proposedcircuit can be observed at Fig. 2. The image in gray representsthe section of the circuit that is not in use. Four operationmodes are presented. In Fig. 2(a), the system operates with

four-leg. In three-leg mode, presented at Fig 2(b), the free-leg denoted byh is not in use. At Fig. 2(c), the system isstill operating in three-leg mode and the free-leg is used tocharge the battery bank, operating as buck converter. Finally,assuming the battery charged, the Fig. 2(d) presents thecondition in which the energy is transferred from the batterybank to the load via inverter, considering the failure at thea.c.input. At this mode, the legh works as boost converter.

Fig. 3. Control block diagram of the proposed configuration.

The proposed system control is shown in 3. The mode ofoperation of the converter is determined by the state of switchSc. If Sc is in position 1, the converter operates accordingto the four-leg mode. IfSc is in position 2, the selectedmode is three-leg. The disconnection of the circulating currentcontrol block makes possible to use the shared-leg to chargethe battery bank.

For the system operating with four-leg, switchesSa, Sb

andSc in position 1, the capacitor d.c.-link voltagevc (vc =E) is adjusted to a reference value by using the controllerRc, which is a standardPI type controller. This controllerprovides the amplitude of the reference currentI∗g . For thepower factor and harmonic control the instantaneous referencecurrent i∗g must be synchronized with voltageeg. This isperformed by the blockGEN -g, from aPLL scheme. Fromthe synchronization witheg and the amplitudeI∗g , the currenti∗g is generated. The current controller is implemented by usingthe controller indicated by blockRi. The controllerRi is adouble sequence digital current controller employed in [21].Thus current controller defines the input reference voltagev∗h.

The instantaneous reference load voltagev∗l can be deter-mined by using the rated optimized load angleδl plus the in-formationθg from blockSY N and the defined load amplitudeV ∗

l . The blockGEN -l uses the input information to generatethe desired reference load voltagev∗l . The homopolar currentio is controlled by controllerRo, that determines voltagev∗oresponsible to minimize the effect of the circulating current io,maintaining this current near to zero. All these voltages areapplied toPWM block to determine the conduction states ofthe converter’s switches.

When the switchSc is in position 2, three-leg mode ofoperation occurs. The d.c./d.c. buck converter is used to chargethe battery bank. The free-leg makes the d.c.-bus voltageVcc tobe stepped down in its average value to supply the d.c.-battery



q

q

q

C

Converter S

ve

i l

C

0

+

+

v l

+

Zl

ic

ei

Le

ee

iig

+

vc

Le

eg

Ce

+ vce

q

q

q

Converter S

vh

+

hi

Lh Lh

Ch

+ vchei

´

´

e

e e

i

´h

hh

´

´

h

h h

qhe

S1

S2

S3

L cc

Battery bank

B

B

A

S4

he

h1

h1

q

(a)

q

q

q

C

Converter S

ve

i l

C

0

+

+

v l

+

Zl

ic

ei

Le

ee

iig

+

vc

Le

eg

Ce

+ vce

q

q

q

Converter S

vh

+

hi

Lh Lh

Ch

+ vchei

´

´

e

e e

i

´h

hh

´

´

h

h h

qhe

S1

S2

S3

L cc

Battery bank

B

B

A

S4

he

h1

h1

q

(b)

q

q

q

C

Converter S

ve

i l

C

0

+

+

v l+

Zl

ic

ei

Le

ee

iig

+

vc

Le

eg

Ce

+ vce

q

q

q

Converter S

vh

+

hi

Lh Lh

Ch

+ vchei

´

´

e

e e

i

´h

hh

´

´

h

h h

qhe

S1

S2

S3

L cc

Battery bank

B

B

A

S4

he

h1

h1

q

(c)

q

q

q

C

Converter S

ve

i l

C

0

+

+

v l

+

Zl

ic

ei

Le

ee

iig

+

vc

Le

eg

Ce

+ vce

q

q

q

Converter S

vh

+

hi

Lh Lh

Ch

+ vchei

´

´

e

e e

i

´h

hh

´

´

h

h h

qhe

S1

S2

S3

L cc

Battery bank

B

B

A

S4

he

h1

h1

q

(d)

Fig. 2. Description of modes of operations: a) Four-leg mode; b)Three-leg mode; c) Three-leg mode charging the battery bank; d) Failure at the a.c. input.

bank according toVbat = DVcc. The battery voltageVbat

is directly proportional to duty ratioD. In the stored-energymode of operation, when the a.c. input voltage is beyond thepermissible tolerance range, the switchS1 disconnects the a.c.input, transferring the energy from the battery bank to the loadvia inverter. Since the battery voltage is low, it is first requiresto be boosted to high d.c. voltage for the proper operation ofthe d.c./a.c. inverter, now responsible to supply the load.Thelow battery voltageVbat is boosted to high d.c. voltageVcc

according toVcc = Vbat/(1−D).When both switchesSa andSb are in position 2, situation

in what the a.c. input voltage failure, the load is supplied bybattery bank and inverter. At this point, the converterSh whowas responsible for regulating the grid current and the d.c.-busvoltage is now responsible for maintaining the voltage appliedto the load.

V. SIMULATION RESULTS

The proposed configuration was simulated using PSIMsoftware with the following parameters described in TABLE

TABLE I

PARAMETERS OF THE SIMULATED SYSTEM.

Parameter ValueDC-bus voltage 300V

Battery bank voltage 48VInductance filter 5.0mHCapacitor filter 70uF

Grid - voltage/frequency (eg) 110V/60HzHarmonic component - amplitude/frequency 0.2eg/180Hz

Load voltage (vl) 110VPower 1.2kV A

RL load 15Ω/2.0mHDiode bridge rectifier connected to RLC 15Ω/2.0mH/2.0mF

I. This configurations does not use transformer in the seriesconnection and consist of four-leg converter. The convertercan be reconfigured to work with three-leg in order to usethe free-leg to charge the battery bank when needed. Thefree-leg is used to compose the buck converter controllingthe duty ratio of the upper switch while the lower is idle.Some simulation results are now presented in Figs. 4, 5, 6and 7. In the simulation results, the capacitors were selected



asC = 2200µF and the switching frequency employed was15kHz. In each figures, there are four subfigures that describe

Fig. 4. Simulation results of the proposed system: grid voltage (eg) and gridcurrent (ig ).

the behavior of the system at certain intervals described as:(a) converter mode of operation of four-leg to three-leg (bothswitchesS2 andS3 will be open) - the shared-leg is denoted bye and the free-leg ish, (b) storing-mode of operation (switchS3 will be close), (c) converter mode of operation of three-leg to four-leg (both switchesS2 andS3 will be close) and(d) the fault at a.c. input grid voltage with its disconnctionfrom switchS1. In Fig 4 is presented the grid voltage, with adisturbance of 20% of third harmonic, and current with powerfactor control near to unity. The THD of grid current is 3.91%and the load current and voltage THD are equal to 31,02% and2,54%. During the storing-mode of operation, when the d.c.voltage level at the battery bank is beyond the preset tolerance,it is observed a certain increase at the grid current amplitudeig, it happens because at this mode of operation the systemneeds to drain more current to maintain the voltage at d.c.-buscapacitors and to charge the d.c.-battery bank (Figs. 4 and 5).During this stage, the grid current THD increases a little to4.36%. The load and grid voltages are also shown in Fig 6. Inall subfigures labeled as (d) are described the moment whenthe fault at a.c. grid voltage occurs and the load is suppliedbyboost converter via free-leg and inverter maintaining the loadvoltage at desired value.

The d.c.-bus voltage is shown in Fig. 7. At timet1, it isdepicted converter mode of operation of four to three-leg.During t2 - t3, it observed the interval the battery bank is beingcharged. The change in the mode of operating of three-leg tofour-leg occurs att4. The battery charging voltage is 48Vcc asobserved in Fig. 7 (b). The presented result illustrates only theinterval the battery bank is being charged taking as referencethe coupling point connectionhB, see Fig. 1(a). Finally, att5,where the a.c. grid voltage failure, it is show the instant thesystem is supplied by battery bank and inverter which keepsthe voltage to the load at the desired value.

Fig. 5. Simulation results of the proposed system: grid current (ig ) and loadcurrent (il).

Fig. 6. Simulation results of the proposed system: grid voltage (eg) and loadvoltage (vl).

(a)

(b)

Fig. 7. Simulation results of the proposed system: a) d.c.-bus voltage. b)battery-bank voltage - storing-mode of operation (from thecoupling pointhB).



TABLE II

PARAMETERS OF THE TEST BENCH.

Parameter ValueDC-bus voltage 250V

Battery bank voltage 48VInductance filter 7.0mHCapacitor filter 70uF

Grid - voltage/frequency (eg) 110V/60HzHarmonic component - amplitude/frequency 0.2eg/180Hz

Load voltage (vl) 110VPower 1.2kV A

RL load 15Ω/2.0mHDiode bridge rectifier connected to RLC 15Ω/2.0mH/2.0mF

VI. EXPERIMENTAL RESULTS

In this section, experimental results of the proposed systemare presented. The system operates at four-legs mode whichis reconfigurable to operate with three-legs in order to chargethe battery bank performing voltage and current compensa-tion. The proposed topology, Fig. 1(a), has been tested byusing a microcomputer-based system which is equipped withdedicated boards, in order to generate the control signals.The system have twelve sensors (six current and six voltagesensors), interface card and data acquisition boards, and twostatic converters each one with three-leg, see Fig. 8. In the

(a)

(b)

Fig. 8. Experimental platform in laboratory:(a) Schematicdiagram of theconverter via PC-based control, (b) Picture of the topology.

experimental tests, the capacitors were selected asC =2200µF and the switching frequency employed was15kHz.The system parameters are presented in TABLE II.

In Fig. 9 are shown the grid current (ig), the grid voltage(eg), the load current (il) and the load voltage (vl). The gridvoltage has been obtained from a disturbance voltage sourceand even in the presence of20% of third harmonic voltage

Fig. 9. Experimental results of the proposed system: grid voltage (eg)and grid current (ig ) [top]; load voltage (vl) and load current (il) [bottom].Vertical: 100 V/div and 5A/div.

at grid; the grid current and the load voltage present thewaveform characteristic close to sinusoidal and with powerfactor control close to one. The grid current THD is 4.36%,while the load current presents THD equal to 29.94%. The loadvoltage THD, for this case, is equal to 2.98%. The voltage

Fig. 10. Experimental results of the proposed system: battery bank voltage(vbat) and d.c.-bus voltage (vcc). Horizontal: 5ms/div.

Fig. 11. Experimental results of the proposed system: load voltage (vl) andload current (il). Vertical: 100 V/div and 5A/div.

of both d.c.-bus voltage and battery bank during the storing- mode of operation are indicated in Fig. 10. For the d.c.-bus voltage and battery bank control it was chosen250Vcc

and48Vcc, respectively. After the fault at a.c. grid voltage theinverter via boost converter keeps the desired voltage to theload, as shown in Fig. 11.

VII. C ONCLUSIONS

An universal active power filter for harmonic and reac-tive power compensation with UPS features for single-phasesystem has been presented. The proposed configuration isa transformerless delta converter with reduced number ofcomponents that that emulates the buck-boost converter from



the shared-leg. The system modelling of the proposed systemshows that the circulating current can be controlled to alevel near to zero. The control of the circulating current isaccomplished by the voltagevo = v′e0 + ve0 − v′h0 − vh0(convertersSe+Sh) in order to control theio close to zero. Inthe three-legs mode of operation, the circulating current doesnot exist. A suitable control strategy for the proposed system,including PWM techniques has also been presented. Thesystem can be reconfigurable to operate with four or three-legleaving the free-leg to charge the battery bank without havinga dedicated d.c./d.c. buck-boost converter. The configurationproduces satisfactory results. The proposed solution has theadvantage of reducing volume and cost in comparison to theconventional UAPF. Simulated and experimental results havebeen presented and validates the operation of the proposedsystem.

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[9] L. P. Kunjumuhammed and M. K. Mishra, “A control algorithm forsingle-phase active power filter under non-stiff voltage source,” IEEETrans. Power Electron., vol. 21, no. 3, pp. 822 – 825, May 2006.

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[21] C. B. Jacobina, M. B. R. Correa, T. M. Oliveira, A. M. N. Lima, andE. R. C. da Silva, “Current control of unbalanced electricalsystems,” inConf. Rec. IEEE-IAS Annu. Meeting, 1999, pp. 1011–1017.

Welflen Ricardo Nogueira Santos was born inSao Luıs-MA, Brazil, in 1979. He has techni-cal/professionalizing course in Electrotechnic and hereceived the B.S. degree in Electrical Engineeringfrom Federal Center of Technological Education ofMaranhao, Sao Luıs-MA, Brazil, in 1998 and 2004,respectively. M.Sc. and Ph.D. degrees in ElectricalEngineering from the Federal University of CampinaGrande, Campina Grande-PB, Brazil, in 2006, and2010, respectively. Since July 2010, he has beenwith the Coordination of Electrical Engineering,

Federal University of Piauı, Teresina, Brazil, where he isnow Professor ofElectrical Engineering Course. He also worked as Maintenance Coordinatorof University Hospital of Federal University of Piauı, Teresina-PI, Brazil,from 2011 to 2013. He was in China, by invitation of Siemens/Trench,to participate of technical inspections (type and routine tests according tointernational standards) about equipments of Siemens/Trench manufacture, involtage levels of 69 kV to 500 kV. The inspections were done inTrenchfactory and Shenyang Institute Co. laboratory, during the period of 16 June to21 July 2014, in Shenyang, China. He is reviewer of the journals SOBRAEP- Power Electronics (Printed), ELSEVIER - International Journal of ElectricalPower and Energy Systems and IEEE Transactions on Power Electronics. Hisresearch interests include Power Electronics, Power Systems, Control Systems,Industrial Automation and Electrical Drives.

Eisenhawer de Moura Fernandes (M’14) wasborn in Brazil in 1981. He received his M.Sc.and Ph.D. degrees in Electrical Engineering fromFederal University of Campina Grande (UFCG),Brazil, in 2006 and 2011, respectively. Since 2008he is with Department of Mechanical Engineering(UFCG), Brazil. In 2013, he was Visiting Professorat the Department of Mechanical Engineering of theUniversity of Wisconsin-Madison, USA, engaged ina research project on self-sensing control of PMmotors. His research interests are Power Electronics,

Motor Drives, Control Systems and Electronic Instrumentation.



Edison Roberto Cabral da Silva (SM’95-F’03)received the B.S.E.E. degree from the PolytechnicSchool of Pernambuco, Recife, Brazil, in 1965, theM.S.E.E. degree from the University of Rio deJaneiro, Brazil, in 1968, and the Dr. Eng. degreefrom the University Paul Sabatier, Toulouse, France,in 1972. From 1967 to 2002, he was with the Elec-trical Engineering Department, Federal Universityof Paraıba, Brazil. From 2002 to 2012, he waswith the Electrical Engineering Department, FederalUniversity of Campina Grande, Brazil, where he

is a Professor Emeritus. He was Director of the Research Laboratory onIndustrial Electronics and Machine Drives for 30 years. In 1990 he waswith COPPE, Federal University of Rio de Janeiro, Brazil, and from 1990 to1991, he was with WEMPEC, University of Wisconsin-Madison,as a VisitingProfessor. He was the General Chairman of the 1984 Joint Brazilian and Latin-American Conference on Automatic Control, sponsored by theAutomaticControl Brazilian Society (SBA), of the IEEE Power Electronics SpecialistsConference (PESC) in 2005 and of the Brazilian Conference onAutomaticControl in 2012. He is a Past-President of SBA. His current research work isin the area of power electronics and motor drives.

Cursino Brandao Jacobina (S’78-M’78-SM’98)was born in Correntes, Pernambuco, Brazil, in 1955.He received the B.S. degree in electrical engineeringfrom the Federal University of Paraıba, CampinaGrande, in 1978, and the Diplome d’Etudes Appro-fondies, and the Ph.D. degrees from Institut NationalPolytechnique de Toulouse, Toulouse, France, in1980 and 1983, respectively. From 1978 to March2002, he was with the Department of ElectricalEngineering, Federal University of Paraıba, CampinaGrande. He has been with the Department of Elec-

trical Engineering, Federal University of Campina Grande,Campina Grande,since April 2002, where he is currently a Professor of electrical engineering.His research interests include electrical drives, power electronics, and energysystems.

Alexandre Cunha Oliveira was born in Fortaleza,Ceara, Brazil, in 1970. He received the Bachelor’s,Master’s and Ph.D.degrees in electrical engineeringfrom the Federal University of Paraıba, CampinaGrande, Paraıba, Brazil, in 1993, 1995, 2003, respec-tively. From 1996 to 2004, he has been a FacultyMember with the Electrical Engineering Depart-ment, Centro Federal de Educacao Tecnologica ofMaranhao, Brazil. Since November 2004, he hasbeen with the Electrical Engineering Department ofFederal University of Campina Grande, Campina

Grande, Paraıba, Brazil, where he is now Professor of Electrical EngineeringCourse. His research interests include electrical drives,power electronics,control systems and energy quality.

Patryckson Marinho Santoswas born in Sao Luıs,Brazil, in 1981. He received the B.S. Degree inindustrial electrical engineering from Federal Centerof Technological Education of Maranhao, Sao Luıs,Brazil, in 2004, and MSc. degree from FederalUniversity of Campina Grande, Campina Grande,Brazil, in 2006. From 2006 to 2007, he was withthe Electrical Engineering Department, Federal Uni-versity of Vale do Sao Francisco. Since 2007, he wasbeen with the Electrical Engineering Department,Federal University of Maranhao, Sao Luıs, where he

is currently a Professor of electrical engineering. His research interest includeelectrical and machines drives, power electronics, energysystems, industrialautomation and intelligent systems.

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