Unified Architecture of Single-Phase Active Power Filter with Battery Interface for UPS Operation

Transcription

1 Proceedngs o the World Congress on Engneerng 2017 Vol I, July 5-7, 2017, London, U.K. Uned Archtecture o Sngle-Phase Actve Power Flter wth Battery Interace or UPS Operaton Tago J. C. Sousa, Vítor Montero, J. G. Pnto, José A. Aonso, Member, IAENG, and João L. Aonso Abstract Ths paper presents a shunt actve power lter wth battery nterace or unnterruptble power supply (UPS) operaton. The proposed uned archtecture s composed by a sngle-phase ac-dc converter rom the power grd sde and by a bdrectonal solated dc-dc converter to nterace the batteres, allowng the operaton n three dstnct modes: (1) Shunt actve power lter; (2) O-lne UPS to supply a set o prorty loads durng power outages; (3) Energy storage system to support the power grd. The proposed archtecture and the developed control algorthms were valdated wth a reduced-scale laboratoral prototype n all the three derent operaton modes. The presented expermental results hghlght the benets o the proposed archtecture. Index Terms Actve Power Flter, Unnterruptble Power Supply, Bdrectonal Isolated dc-dc Converter, Power Qualty. I. INTRODUCTION Nowadays, electrcal energy s ndspensable to the comort and needs o socety. However, due to the everlastng utlsaton o nonlnear loads, harmonc currents low n the power grd, pollutng t [1]. Once power qualty problems lead to nancal costs, t s o utmost mportance to mtgate these power qualty ssues [2]. A shunt actve power lter (SAPF), whose concept was proposed n 1971 [3], s a power electroncs based equpment capable o mtgatng harmonc currents and compensatng power actor o a set o loads connected to the power grd [4]. A lne-commutated SAPF or undamental reactve power compensaton was made practcable n [5], and a ull-controlled SAPF also allowng harmonc currents compensaton was proposed n [6]. A SAPF s comprsed by an ac-dc bdrectonal converter connected n parallel wth the power grd, provdng the harmonc currents and reactve power consumed by the loads, allowng the power grd to supply only actve power,.e., a snusodal current n phase wth the power grd voltage. Over the last decades, extensve research has been made n terms o new compensaton capabltes, topologes and control schemes or SAPFs. A Manuscrpt receved March 18, Ths work s supported by FCT wth the reerence project UID/EEA/04436/2013, by FEDER unds through the COMPETE 2020 Programa Operaconal Compettvdade e Internaconalzação (POCI) wth the reerence project POCI FEDER Tago J. C. Sousa s wth Centro Algortm, Unversty o Mnho, Campus o Azurem, Gumaraes, , Portugal (e-mal: a61909@alunos.umnho.pt) Jose A. Aonso s wth CMEMS-UMnho, Unversty o Mnho, Campus o Azurem, Gumaraes, , Portugal (phone: ; ax: ; e-mal: jose.aonso@de.umnho.pt). Vítor Montero, J. G. Pnto and João L. Aonso are wth Centro Algortm, Unversty o Mnho, Campus o Azurém, Gumarães, , Portugal (e-mal: {vmontero, gpnto, jla}@de.umnho.pt). wdespread revew about SAPF or power qualty mprovement s presented n [7]. Besdes problems assocated wth currents, there are power systems where t s mandatory to ncessantly provde power to specc loads. In ndustres, power outages can be relected n producton alure, whch carres large nancal costs. In [8] are presented some examples about how power outages nlct costs n sectors lke nancal tradng, computer centres and telecommuncatons. Unpredcted power outages can be manly trggered by natural catastrophes, e.g., lghtnng strkes and earthquakes, and can last or mnutes or even days. In medcal acltes, power outages can be hazardous to human le, causng respratory ssues, nablty to sterlze nstruments, processng X-rays and to properly transport patents between loors due to unavalable elevators [9]. Towards the reerred consequences, t s crucal or a power system to be prepared or power outages, requrng the utlsaton o an energy backup. An unnterruptble power supply (UPS) allows a ceaselessly delver o electrcal power or a set o prorty loads. Several UPS topologes have been developed wth derent protecton levels, as well as ecency and cost related dversty [10]. Analysng a SAPF and an o-lne UPS system rom the power grd pont o vew, t s possble to denty that the power converter o both systems s very smlar, comprsng a parallel grd-connected ac-dc converter [11]. However, an o-lne UPS has an addtonal converter to charge the batteres. Thereore, connectng a dc-dc converter to the dc sde o the SAPF, t s possble to endow the SAPF wth the eatures o an o-lne UPS. In [12] s proposed an o-lne UPS wth actve lterng capabltes usng a hgh-requency transormer and a cycloconverter. However, t requres our bdrectonal cells, each one beng comprsed by several power semconductors, leadng to hgher conducton losses. In [13] s presented a modular UPS system wth actve lterng capabltes, but the SAPF and the modular UPS consst o derent power converters. The combned operaton o SAPF and UPS s studed n [14] or a three-phase system, however, usng a non-solated dc-dc converter, requrng a large battery pack or grd connected applcatons. In ths context, ths paper proposes a sngle-phase uned archtecture o a SAPF wth battery nterace or UPS operaton,.e., wth an energy storage nterace. The proposed archtecture s composed by an ac-dc converter connected n parallel wth the power grd (.e., smlarly to a tradtonal SAPF), and by a bdrectonal solated dc-dc converter (.e., smlarly to the dc-dc converter o an o-lne UPS). The ac-dc converter can operate as a SAPF producng

2 , July 5-7, 2017, London, U.K. Power Grd s L Loads ac-dc converter dc-dc converter s 1 s 3 s 11 s 9 s 5 s 7 R C L C 2 L 2 L 1 v 2 v 1 C 1 v bat Batteres s 2 s 4 s 12 s 10 s 6 s 8 Fg. 1. Electrcal crcut o the uned archtecture o actve power lter wth energy storage nterace. the harmonc currents and reactve power requred by the loads and chargng the batteres at the same tme, or as UPS producng a snusodal voltage to eed the loads. On the other hand, the bdrectonal solated dc-dc converter can be controlled to charge the batteres (wth constant voltage and constant current) or dscharge the batteres durng the operaton as an o-lne UPS. It s mportant to note that the operaton as o-lne UPS only occurs durng power outages,.e., the control algorthm dentes the power outage and changes the control algorthm or such operaton mode. Moreover, once the dc-dc converter s solated, t s possble to use a smaller battery pack, snce a hgher converson rato can be acheved wth a hgh-requency transormer compared to non-solated topologes, representng an mportant contrbuton o the proposed archtecture. II. PRINCIPLE OF OPERATION Ths secton presents the prncple o operaton o the proposed uned archtecture o SAPF wth battery nterace or UPS operaton. Fg. 1 shows the electrcal crcut o the uned archtecture. As t can be seen t s composed by two power converters: a bdrectonal ac-dc converter to nterace the power grd, and a bdrectonal solated dc-dc converter to nterace the batteres. These two converters are analysed n detal along ths secton. A. Ac-dc Converter The ac-dc converter s a ull-brdge topology composed by two legs. Ths converter s used durng all the three derent operaton modes. Durng the operaton as SAPF t s controlled as a current source to control the grd current. The reerence or the grd current s obtaned wth the Fryze-Buchholz-Depenbrock (FBD) power theory proposed n [15][16]. Wth ths theory t s calculated the actve power consumed by the loads n order to determne the n-phase, undamental current desrable to be provded by the power grd. Thus, the SAPF must supply the harmonc content and reactve power demanded by the loads. The reerence current or the SAPF ( * ) s obtaned accordng to: * Pvs L, 2 (1) V where L s the load current, P s the actve power consumed by the loads, s the power grd voltage, and V s 2 s the S squared rms power grd voltage. It s mportant to note that, n the presence o a dstorted power grd voltage, the grd current wll also be dstorted. Snusodal grd current can be obtaned usng a slght modcaton n the presented control theory, whch conssts n usng the undamental component o the power grd voltage nstead o the measured ones. The undamental component o the power grd voltage can be determned by means o a phase-locked loop (PLL) algorthm. The current produced by the SAPF s controlled by means o a PI. The dc-lnk voltage s controlled accordng to ts reerence also usng a PI controller to generate the regulaton power (p reg). Ths varable represents an addtonal power component that must be provded by the power grd to control the voltage across the dc-lnk capactors. Thereore, P s replaced by P + p reg n order to determne the SAPF reerence current. Besdes the operaton as SAPF, durng ths operaton mode the ac-dc converter can also be used to transer energy rom the power grd to charge the batteres through the bdrectonal solated dc-dc converter. Thereore, another power component s added to the SAPF reerence current, accordng to: ( P preg pbat ) * L 2 VS v, (2) where pll s the undamental component o the power grd voltage obtaned by means o a PLL, and p bat s equal to the product o batteres current and batteres voltage, meanng the addtonal power demanded by the SAPF n order to charge the batteres wth the desred current and voltage. Durng the operaton as UPS, the ac-dc converter s controlled as a voltage source to obtan a snusodal output voltage to eed the loads durng the power outages. The reerence voltage s obtaned wth the PLL algorthm. The output voltage s controlled usng a dual-loop PI controller, where are used the voltage produced by the converter, the current consumed by the loads (whch s the same as the converter output current) and ts dervatve. The output reerence voltage o the converter (v re) s obtaned accordng to: v re k k v k k v k pv err um _ err k p k spll k d k, (3)

3 , July 5-7, 2017, London, U.K. where v err s the output voltage error, umerr s the output voltage error sum, s the output current, T s s the samplng perod and k xx are controller gans, where the rst ndex (p, or d) means the controller component (proportonal, ntegral or dervatve) and the second ndex (v or ) represents voltage or current quanttes. The output current dervatve Δ s determned accordng to: k k k 1. (4) TS In the scope o ths paper, t was used a PI controller or the output voltage and a proportonal-dervatve (PD) controller or the output current n order to acheve a sutable perormance n the presence o nonlnear loads. B. Bdrectonal Isolated dc-dc Converter The dc-dc converter conssts n a voltage-ed dual-actve-brdge topology, where the prmary sde s the low-voltage sde and s connected to the batteres and the secondary sde s the hgh-voltage sde, sharng the dc-lnk wth the ac-dc converter. Both sdes are connected by a hgh-requency transormer, allowng solaton and a hgh voltage converson rato. The dual-actve-brdge topology can be operated usng modulaton technques lke pulse-wdth modulaton (PWM), phase sht and devatons rom the latter. Phase sht [17] allows a lexble power transer between both sdes o the converter, beng one o the most popular modulaton technques appled to solated dc-dc converters, such the presented topology. Each sde o the converter produces a 50% duty-cycle square-wave, beng appled a phase sht between both voltages. The appled phase angle has drect mpact n the transerred power, wth the latter ncreasng wth the phase sht. Besdes, phase sht modulaton allows actve rectcaton, as opposed to PWM, where one converter sde s swtched at each tme. When low voltage values are nvolved, the latter brngs a reduced ecency due to the voltage drops on the output antparallel dodes [18]. Despte the aorementoned advantages, however, phase sht modulaton s not sutable when the voltages appled to the transormer wndngs are dscrepant wth respect to transormer turns rato. Ths stuaton leads to substantal currents n the transormer, as well as n the power swtches, even the transerred power s low. Thus, the converter operates wth hgh values o reactve power. To overcome ths ssue, varants o the phase sht modulaton technque were developed, e.g., dual phase sht [19] and trple phase sht [20]. These modulaton technques apply, respectvely, two or three dstnct phase angles to the converter, usng a phase derence between two legs o the same brdge. Thus, crculatng currents and consequently reactve power can be reduced usng these modulaton technques. In addton, both PWM and phase sht modulaton technques can be combned n order to reduce the reactve power nvolved [21]. Thereore, a phase sht modulaton technque combned wth duty-cycle control was mplemented or power transer, reducng the current stress n the swtches and transormer wndngs. The duty-cycle value s obtaned wth a PI controller, generatng hgh values o duty-cycle when the dc sde converter voltages have a close relatonshp n respect wth the transormer turns rato and low values o duty-cycle or the opposte case. The phase angle s obtaned also by means o a PI controller and s responsble or dc-lnk voltage regulaton when the system s operatng n UPS mode and controls the chargng o the batteres when the system operates as SAPF. III. DEVELOPED PROTOTYPE Ths secton shows n detal the developed laboratoral prototype, manly ocusng the dgtal control structure and the hardware power structure. Fg. 2 shows the laboratoral workbench, ncludng the developed prototype, and Table I presents the man parameters o ths prototype. A. Control Structure In order to control the aorementoned power converters t was used a dgtal control structure. The man core o such structure s the dgtal sgnal processor (DSP) model TMS320F28377S rom Texas Instruments, where are mplemented the dgtal control algorthms. Ths DSP has ncorporated an nternal ADC wth 14 channels and wth 12 bts o resoluton, as well as an nternal DAC wth 8 channels and wth 12 bts o resoluton, and several PWM output channels. The voltages and currents are acqured wth the CYHVS5-25A and HAIS 50-P hall-eect sensors. The output sgnals o such sensors are bpolar and n current, thereore, t s used a sgnal condtonng crcut to converter the current sgnals to voltage sgnals, as well to adapt the voltage range o each sgnal to the unpolar voltage o the ADCs channels. The sgnal condtonng s processed usng a summng ampler crcut. The output control sgnals rom the DSP are processed by a command crcut wth the ntent to convert the 3 V transstor-transstor logc (TTL) sgnals o the DSP to 15 V complementary metal-oxde-semconductor (CMOS) logc sgnals. In ths command crcut t s also used a protecton crcut, whch s actvated rom the sgnal condtonng crcut,.e., some o the voltages or currents exceeds a nomnal predened value, then an error s deployed to control the command crcut. The output sgnals rom the command crcut are then used as nput or the IGBT and MOSFET gate drver crcuts. These gate drvers are based n the ADUM3223 rom Analog Devces. In the scope o ths project were used 6 drver crcuts, once each one s able to control two power semconductors. B. Power Structure As descrbed n secton II, the power structure s dvded n two man converters, the ac-dc and the bdrectonal solated dc-dc. These converters are descrbed as ollows. 1) Ac-dc Converter The ac-dc converter s a ull-brdge converter and s composed by our IGBTs model IKW40N65F5 rom Inneon Technologes (maxmum collector-emtter voltage o 650 V and maxmum collector current o 40 A). In the scope o ths project, these IGBTs are swtched at 50 khz, In order to prevent malunctons t s used a protecton crcut or the gate,.e., a crcut between the drver and the gate and emtter termnals o the IGBT. In order to couple the ac-dc converter wth the power grd t s used an nductor wth nomnal nductance o 1.2 mh and nomnal current o 20 A. Addtonally to ths nductor t s used a RC passve

4 , July 5-7, 2017, London, U.K. Input Inductor Power Converters Drver Boards DSP and Control Board used 59 AWG25 wres n parallel) and the secondary nomnal current s 3 A (were used 3 AWG23 wres n parallel). Hgh-Frequency Transormer Dc-lnk Capactors Hall-Eect Sensors Fg. 2. Laboratoral workbench wth the developed prototype. Table I. Man parameters o the developed prototype. Parameter Value Power Grd Voltage 230 V Power Grd Frequency 50 Hz Maxmum Grd Current 16 A Dc-lnk Voltage 400 V Swtchng Frequency (ac-dc) 50 khz Swtchng Frequency (dc-dc) 100 khz Hgh-Frequency Transormer Rato 1:15 Maxmum Power as UPS 1 kw Batteres Voltage 23 V to 29 V Batteres Current 40 A lter wth a capactance o 10 µf and resstance o 8 Ω. The 8 Ω resstor s appled wth the purpose o damp possble resonances between the capactve and nductve elements o the passve lter. For the dc-lnk are used our capactors model MAL E3 rom Vshay n order to perorm a nomnal capactance o 3.28 mf wth a maxmum voltage o 450 V. 2) Bdrectonal Isolated dc-dc Converter The dc-dc converter s a dual-actve-brdge dc-dc converter composed by our MOSFETs model PSMN015-60PS rom NXP Semconductor (maxmum dran-source voltage o 60 V, maxmum dran current o 50 A, and dran-source on-resstance o 14.8 mω) and our MOSFETs model IPP50R500CE rom Inneon Technologes (maxmum dran-source voltage o 500 V, maxmum dran current o 11 A and dran-source on-resstance o 500 mω). In the scope o ths project, these MOSFETs are swtched at 100 khz, and, smlarly to the IGBTs o the ac-dc converter, t s used a protecton crcut or the gate,.e., a crcut between the drver and the gate and source termnals o the semconductor. In the batteres sde t s used a capactor wth nomnal capactance o 4.7 mf and nomnal voltage o 63 V. The galvanc solaton between the prmary and secondary converters s perormed usng a 1:15 hgh-requency transormer specally developed or ths project usng errtes model B66397G0000X187 rom Epcos. The prmary nomnal current s 45 A (were IV. EXPERIMENTAL VALIDATION Ths secton presents the man expermental results obtaned to prove the proper operaton o the proposed uned archtecture and to hghlght ts man benets. Thereore, ths secton s dvded n three dstnct modes o operaton: SAPF; UPS; and energy storage system. A. Operaton as SAPF Ths tem presents the operaton o the proposed uned archtecture durng the operaton as SAPF. The rst process o ths operaton mode s the synchronzaton wth the undamental component o the power grd voltage, where s used the phase-locked loop (PLL) algorthm proposed n [22]. Ater that, consderng the current consumed by the loads connected n the same electrcal nstallaton, t s determned the reerence current that the converter must produce n order to obtan a snusodal grd current. The detals about the determnaton o the grd reerence current are presented n secton II (a). Fg. 3 shows the expermental results obtaned wth the developed laboratory prototype durng the operaton as SAPF. In ths gure t s possble to see the power grd voltage (), the load current ( L), whch s the grd current ( s), the dc-lnk voltage (), and the converter current reerence ( c * ) calculated by the DSP. From ths gure t s possble to see that the current consumed by the loads ( L) has a hgh harmonc dstorton and, consequently, to cancel such harmonc dstorton, the determned converter current reerence ( c * ) has also a hgh harmonc dstorton. In ths expermental result, t s mportant to note that the dc-lnk voltage s not yet controlled to ts reerence,.e., the converter only determnes the reerence current and s not yet compensatng the currents. Fg. 4 shows the power grd voltage (), the grd current ( s), and the dc-lnk voltage () durng the operaton as SAPF. As t can be seen, due to ths operaton mode, the grd current ( s) s snusodal wth reduced harmonc dstorton (THD% = 3.6%), and n phase wth the power grd voltage (),.e., rom power grd pont o vew, the electrcal nstallaton only operates wth undamental actve power. It s also mportant to note that the dc-lnk voltage s regulated to the reerence value, mantanng a proper value n order to allow the accurate operaton o the SAPF. B. Operaton as UPS Ths tem presents the operaton o the proposed uned archtecture durng the operaton as UPS. Ths operaton mode only occurs durng power outages, when control changes, so that the ac-dc converter stops operatng as SAPF, and begns to produce a snusodal voltage to eed the electrcal loads. Thereore, the rst algorthm s the detecton o power outages. For such purpose t was used the hal-cycle rms value o the power grd voltage to detect when t alls below a threshold o 10% o the nomnal value. Fg. 5 shows the power grd voltage (), the rms value o the power grd voltage (V s) and a lag used to ndcate when

5 , July 5-7, 2017, London, U.K. c * L outage V S Fg. 3. Expermental results durng the operaton as actve power lter: Power grd voltage (); Load current ( L); Dc-lnk voltage (); Converter current reerence ( c * ). s Fg. 5. Expermental results durng the operaton as UPS: Power grd voltage (); Rms value o the power grd voltage (V s); Flag used to ndcate a power outage (outage). v Fg. 4. Expermental results durng the operaton as actve power lter: Power grd voltage (); Grd current ( s); Dc-lnk voltage (). a power outage s detected. As t can be seen, a power outage occurs durng the postve hal-cycle approxmately at 30 0, and the DSP takes approxmately 2 mllseconds to denty the power outage. As aorementoned, when a power outage occurs, the control algorthm s changed to the ac-dc converter produce a voltage. Fg. 6 shows the power grd voltage () and the current consumed by the loads ( ) durng the operaton as UPS. As t can be seen, due to the control algorthm used by the ac-dc converter durng ths operaton mode, the voltage produced s snusodal even wth a dstorted current consumpton, representng an added value o the proposed uned archtecture. Besdes the ac-dc converter, durng ths operaton mode, t s necessary to use the bdrectonal solated dc-dc converter. Thereore, Fg. 7 shows the voltage appled to the prmary wndng o the solated transormer (v 1), the voltage appled to the secondary wndng o the solated transormer (v 2), the current n the prmary wndng ( 1), and the dc-lnk voltage (). As expected, due to the control algorthm (descrbed n secton II), the voltage n the secondary wndng s not n phase wth the voltage n the prmary wndng to enable the power transer. C. Operaton as Energy Storage System Ths tem presents the operaton o the proposed uned archtecture durng the operaton as energy storage system,.e., when both ac-dc and dc-dc converter are used to charge the batteres. It s mportant to note that ths operaton mode Fg. 6. Expermental results durng the operaton as UPS: Converter output voltage (v ); Load current ( ); Dc-lnk voltage (). can be perormed wth the ac-dc converter operatng as SAPF. The energy stored n the batteres can be used n two dstnct scenaros: (1) It can be njected nto the power grd durng the operaton o the ac-dc converter as SAPF; (2) It can be used to eed the electrcal loads durng power outages,.e., durng the operaton as UPS. The man expermental results o the operaton o both ac-dc and dc-dc converters n these scenaros were presented n the prevous tems. Nevertheless, takng nto account the mportance o the solaton transormer, Fg. 8 shows the voltage n the prmary wndng o the transormer (v 1), the voltage n the secondary wndng o the transormer (v 2), the current n the prmary wndng ( 1), and the batteres voltage (v bat). As t can be seen, n Fg. 7 the prmary wndng voltage o the hgh-requency transormer leads the secondary wndng voltage (.e., the energy lows rom the batteres to the dc-lnk), and n Fg. 8 the prmary wndng voltage lags the secondary wndng voltage (.e., the energy lows rom the dc-lnk to the batteres). V. CONCLUSION Ths paper presented a uned archtecture o sngle-phase shunt actve power lter wth battery nterace or unnterruptble power supply (UPS) operaton. Along the paper s ntroduced the prncple o operaton and s perormed a detaled descrpton o the developed control and power crcuts ncludng the appled control algorthms.

6 , July 5-7, 2017, London, U.K. v 1 1 v 2 Fg. 7. Expermental results durng the operaton as UPS: Voltage n the prmary wndng o the transormer (v 1); Voltage n the secondary wndng o the transormer (v 2); Current n the prmary wndng ( 1); Dc-lnk voltage (). v 2 v 1 1 v bat Fg. 8. Expermental results durng the operaton as energy storage system: Voltage n the prmary wndng o the transormer (v 1); Voltage n the secondary wndng o the transormer (v 2); Current n the prmary wndng ( 1); Batteres voltage (v bat). The expermental results were obtaned to valdate the proposed ntegrated archtecture and the control algorthms through three dstnct modes o operaton: (1) Shunt actve power lter; (2) Isolated UPS to supply a set o prorty loads durng power outages; (3) Energy storage system to support the power grd. The proposed system can be an optmal soluton or sngle-phase nstallatons, allowng the compensaton o power qualty problems related wth current harmoncs, power actor and power outages. [6] H. Akag, Y. Kanazawa, A. Nabae, Instantaneous Reactve Power Compensators Comprsng Swtchng Devces wthout Energy Storage Components, IEEE Trans. Ind. Appl., vol.ia-20, no.3, pp , May [7] B. Sngh, K. Al-Haddad, and A. Chandra, A Revew o actve lters or power qualty mprovement, IEEE Trans. on Ind. Electron., vol.46, no.5, pp , Oct [8] Nel Hodge, Energy Rsks - the dangers o power cuts and blackouts, Emergng Rsks (Allanz), pp.28-33, [9] Healthcare & Publc Health Sector Coordnatng Councls, Plannng or Power Outages: A Gude or Hosptals and Healthcare Facltes, [10] J. P. Beaudet, J. N. Forna, and O. Pnon, UPS topologes and standards, MGE-UPS Systems, [11] A. Emad, A. Nasr, and S. B. Bekarov, Unnterruptble Power Supples and Actve Flters. CRC Press, [12] V. John and N. Mohan, Standby power supply wth hgh requency solaton, IEEE APEC Appled Power Electroncs Conerence and Exposton, pp , Mar [13] Ch Zhang, Josep M. Guerrero, Juan C. Vasquez, A smpled control archtecture or three-phase nverters n modular UPS applcaton wth shunt actve power lter embedded, ECCE Internatonal Conerence on Power Electroncs, pp , June [14] Bruno Exposto, J. G. Pnto, H. Goncalves, Vtor Montero, D. Pedrosa, C. Couto, J. L. Aonso, Evaluaton o a Shunt Actve Power Flter wth energy backup capablty, IEEE IECON Industral Electroncs Conerence, pp , Nov [15] M. Depenbrock, The FBD-method, a generally applcable tool or analyzng power relatons, IEEE Trans. Power Syst., vol.8, no.2, pp , May [16] Telmo Santos, J. G. Pnto, P. Neves, D. Gonçalves, João L. Aonso, Comparson o Three Control Theores or Sngle-Phase Actve Power Flters, IEEE IECON Industral Electroncs Socety Conerence, Nov [17] R. W. A. A. De Doncker, D. M. Dvan, M. H. Kheraluwala, A Three-Phase Sot-Swtched Hgh-Power-Densty DC/DC Converter or Hgh-Power Applcatons, IEEE Trans. Ind. Appl., vol.27, no.1, pp.63 73, Jan [18] J. Sebastan, J. A. Cobos, O. Garca, J. Uceda, An overall study o the hal-brdge complementary-control DC-to-DC converter, IEEE PESC Power Electroncs Specalst Conerence, vol.2, pp , June [19] Hua Ba, Chrs M, Elmnate Reactve Power and Increase System Ecency o Isolated Bdrectonal Dual-Actve-Brdge DC DC Converters Usng Novel Dual-Phase-Sht Control, IEEE Trans. Power Electron., vol.23, no.6, pp , Dec [20] Kuyuan Wu, Clarence W. de Slva, Wllam G. Dunord, Stablty analyss o solated bdrectonal dual actve ull-brdge DC-DC converter wth trple phase-sht control, IEEE Trans. Power Electron., vol.27, no.4, pp , Apr [21] Dehong Xu, Chuanhong Zhao, Haeng Fan, A PWM plus phasesht control bdrectonal dc-dc converter, IEEE Trans. Power Electron., vol.19, no.3, pp , May [22] M. Karm-Gharteman, M. R. Iravan, A new phase-locked loop (PLL) system, IEEE MWSCAS Mdwest Symposum on Crcuts and Systems, vol.1, pp , Aug REFERENCES [1] A. Araújo, J. G. Pnto, B. Exposto, C. Couto, and J. L. Aonso, Implementaton and Comparson o Derent Swtchng Technques or Shunt Actve Power Flters, IEEE IECON Industral Electroncs Socety Conerence, pp , Nov [2] Roger C. Dugan, Mark F. McGranaghan, S. Santoso, H. W. Beaty, Electrcal Power Systems Qualty, McGraw-Hll (3rd Edton), pp , [3] H. Sasak, T. Machda, A new method to elmnate ac harmonc currents by magnetc lux compensaton - consderatons on basc desgn, IEEE Trans. Power App. Syst., vol.pas-90, no.5, pp , [4] J. G. Pnto, Bruno Exposto, Vtor Montero, L. F. C. Montero, Carlos Couto, João L. Aonso, Comparson o Current-Source and Voltage- Source Shunt Actve Power Flters or Harmonc Compensaton and Reactve Power Control, IEEE IECON Industral Electroncs Socety Conerence, pp , Oct [5] L. Gyugy, E. C. Strycula, Actve AC Power Flters, IEEE IAS Industry Applcatons Socety Annual Meetng, pp , 1976.