Adaptive Hysteresis Band Current Control for Transformerless Single-Phase PV Inverters

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1 Adaptve Hytere Band Current Control for Tranformerle Sngle-Phae Inverter Gerardo Vázquez, Pedro Rodrguez Techncal Unverty of Catalona Department of Electrcal Engneerng Barcelona SPAIN Rafael Ordoñez Technologcal Inttute of Apzaco Department of Electronc Engneerng Tlaxcala, Méxco Tamá Kereke, Remu Teodorecu Aalborg Unverty Inttute of Energy Technology Aalborg DENMARK Abtract.-Current control baed on hytere algorthm are wdely ued n dfferent applcaton, uch a moton control, actve flterng or actve/reactve power delvery control n dtrbuted generaton ytem. The hytere current control provde to the ytem a fat and robut dynamc repone, and requre a mple mplementaton n tandard dgtal gnal platform. On the other hand, the man drawback of clacal hytere current control le n the fact that the wtchng frequency varable, a the hytere band fxed. In th paper a varable band hytere control algorthm wll be preented. A t wll be hown, th varable band permt overcomng the aforementoned problem gvng re to an almot contant wtchng frequency. The performance of th algorthm, together wth clacal hytere control and proportonal reonant (PR) controller, ha been evaluated n three dfferent ngle-phae nverter topologe, by mean of mulaton performed wth PSIM. In adon, the behavor of the thermal loe when ung each control tructure n uch converter ha been tuded a well. I. INTRODUCTION The clacal current control technque for power converter, baed on PWM modulaton, preent a certan control delay that doe not permt to control accurately the ntantaneou-peak of the current that are beng delvered by a power converter []. In order to olve th ue, aynchronou ne-trangle PWM voltage control can be ued n conjuncton wth ntantaneou current feedback control. However, when th method ued the error gnal are nearly nuodal and the dynamcal repone of the ytem lmted by the tablty bandwh of the feedback loop. The ue of predctve voltage control technque [2] permt mprovng the bandwh of the controller, a the trackng of the reference doe not depend excluvely on the controller tunng, but alo on the feedforward control gnal provded by the predctve algorthm. Although thee technque tend to gve optmum performance n term of repone and accuracy, they depend hghly on the accuracy of the predctve model and they are omehow complcated to mplement n tandard Dgtal Sgnal Proceor (DSP) [3,4]. A an alternatve to PWM technque hytere current controller have been broadly ued alo, a they can be ealy mplemented wth no complex hardware. Another mportant advantage of th knd of controller t fat dynamc repone and ther nherent capablty to lmt the peak current njected by the converter. In adon, hytere controller do not requre any nformaton about the ytem parameter, omethng that enhance t robutne. In clacal hytere controller the error band normally fxed to a certan value. A a conequence the wtchng frequency vare wthn a band becaue peak-to-peak current rpple mut be controlled at all pont of the fundamental frequency wave. In order to olve th problem wthout damagng the good dynamcal performance of the hytere current control, an adaptve hytere band able to mantan a contant wtchng frequency propoed n th paper. In the followng the algorthm that ha been developed n order to calculate the value of the hytere band wll be detaled. ater on ther performance wll be teted n three dfferent power converter topologe ued for ngle phae applcaton. The reult obtaned wth the new algorthm wll be compared wth thoe obtaned when ung clacal hytere and PR controller. Th analy wll be extended a well to the thermal loe that appear n the power converter n each cae. Vdc II. BASIC HYSTERESIS CURRENT CONTRO The bac hytere current control baed on an on-lne PWM control that fxe the output voltage of the nverter ntantaneouly [5]. The man tak of the PWM current controller n an nverter to adjut the output current,, n order to track the current reference provded by. Comparng the ntantaneou current n the load wth the reference gnal the controller hould adjut the duty cycle of the PWM gnal n the nverter. A a conequence, the error gnal (δ ) hould be reduced [6]. A bac cheme of the PWM current controller hown n Fg.. S PWM Current Controller Fg.. Bac Current Control Scheme n a ngle phae nverter. δ AC Sde oad /9/$ IEEE 73

2 In th knd of controller, the output voltage level depend on the error between the current etpont and the real current njected by the converter. In th way when the load current lower than the current reference, the nverter connect the potve de of the DC bu to the load, reducng thu the current. On the contrary when the load current hgher than the current reference, the nverter connect the negatve de of the DC bu to the load. Takng nto account the prevou decrpton, the error gnal can be mantaned wthn a certan fxed band. Fg. 2 how the evoluton of the load current when ung a bac hytere current control. d d 2 2h (3) t T t 2 2 Fg. 3 how a nverter wth H5 tructure [8]. Durng the potve emcycle when wtche, and are ON and, are OFF, an actve vector appled to the load. Th wtchng emperod correpond to t n Fg. 2 when the current ncreang. In order to apply a zero voltage vector to the load, turn off wherea,,, and reman n the ame tate. Th wtchng perod correpond to t 2 n Fg. 2 when the current decreang (freewheelng cae). The equvalent crcut n both perod are hown n Fg h Clnk t t2 T S Fg. 3. Bac tructure of a H5 nverter. Fg. 2. nverter Output current wth hytere control. V However, and n pte of t good dynamc repone, th fxed error band make the wtchng frequency vary accordng to the lope of the reference gnal. Th varable wtchng frequency may caue everal problem n the ytem uch a: overheatng of the converter, dffculty n the flter degn, reonance and appearance of nonoptmum current rpple n the load [7]. In order to overcome the aforementoned problem the bac hytere current control ytem can be modfed n order to get an almot contant wtchng frequency. In the followng ecton t wll be hown how, t poble to degn an adaptve hytere band algorthm for a ngle phae nverter able to keep a contant wtchng frequency. III. PROPOSED HYSTERESIS CURRENT CONTRO Conderng that the output current of the nverter the one hown n Fg. 2, the error gnal can be wrtten a (): δ () where the output current and the reference current. It poble to deduct an equaton for each wtchng perod wrtten n (2) and (3). Accordng to Fg 2, for [, t ]: And for [t 2,T ]: d d t T 2h t (2) (b) Fg. 4.Equvalent crcut (a) actve voltage vector, (b) zero voltage vector. Accordng wth the equvalent crcut hown n Fg. 4, t poble to etablh the equaton for the equvalent crcut n both perod (4) and (5). V C V d + d V + Subttutng equaton (2) and (3) n equaton (4) and (5) repectvely t poble to obtan the followng equaton: (a) V (4) (5) /9/$ IEEE 74

3 V C d t h 2 (6) C D D3 d V t h 2 2 Addng equaton (6) and (7): (7) C2 A D2 B D4 D5 D D2 D3 D4 2 Clnk A T d t + (8) VC Fnally, by mean of ubttutng the equaton (8) n equaton (6) and mplfyng term equaton (9) reached: T h V 2 d d + + VC D D2 B D3 D4 S6 D D2 2 Equaton (9) defne an adaptve hytere band that depend on the ytem parameter. Th algorthm permt to obtan a contant wtchng frequency n the nverter load. The ame analy can be performed for other topologe lke HERIC (Hgh Effcency Relable Inverter Concept) [9], hown n Fg. 5, or HB-ZVR (Half-Brdge Zero Voltage Rectfer) [], depcted n Fg. 6. Fg. 5. Hgh Effcent and Relable Inverter Concept (HERIC) topology. In the HERIC topology durng the potve half cycle S6 reman connected, wherea and commutate at wtchng frequency n order to generate both actve and zero vector. When an actve vector preent ( and are ON), current flow from the panel to the load (grd), when a zero vector occur, and are wtched OFF and then, the current flow through S6 and D, th the freewheelng tuaton. On the other hand, when the negatve cycle comng, S6 goe OFF and goe ON, wherea and commutate at wtchng frequency. Th mean that an actve vector preent when and are ON, therefore the current flow from the panel toward the load, thu when and turn off, a zero voltage vector preent n the load, then current flow through and D2. Th knd of modulaton permt havng a freewheelng tuaton wth no connected load (utlty grd). (9) Fg. 6. Half-Brdge Zero Voltage Rectfer (HB-ZVR) topology. In turn the HB-ZVR topology, Fg. 6, t provde the actve vector ung a conventonal full-brdge nverter, wherea the zero voltage vector are generated by the ngle phae rectfer and. Th topology work a follow: durng potve emcycle, when an actve vector appled, wtche and are ON, and, and are OFF, n th tuaton the output current ncreang. In order to apply a zero voltage vector, and are turn off and turn on, n th cae, the current decreang. On the other hand, n the negatve em-cycle, an actve vector appled when and are ON, and, and are OFF, wherea a zero voltage vector appled when,, and are OFF and ON. In the next ecton, mulaton reult ung hytere current control were performed n order to compare the ytem performance wth and wthout adaptve hytere band. All mulaton were performed ung PSIM (Thermal Module). The IGBT an IPM (Intellgent Power Module) from Mtubh PM75DSA2. In th tudy cae the DC bu wa of 4V, whle the load wa a grd wth 4 mh, 325V pk and f 5Hz. IV. SIMUATION RESUTS In th ecton mulaton wth H5, HERIC and HB-ZVR topologe have been carred out. The mulaton reult ung the adaptve band hytere algorthm n the H5, HERIC and ZB-ZVR topologe are hown n Fg. 7, Fg. 8 and Fg. 9 repectvely. Fg. 7. Behavor of the current and the voltage at the output of the converter when ung the H5 topology /9/$ IEEE 75

4 A can be een n Fg., n cae (a) the wtchng frequency varable over a wde frequency range and n the cae (b) the wtchng frequency reman around khz. Th charactertc permt to degn ealy the output flter of the nverter. In the next ecton t preented ome mulaton reult regardng wtchng and conducton loe for thee three topologe. The IGBT model ued n thee mulaton wa obtaned by mean IGBT dataheet and after that, wa loaded to PSIM lbrary. Fg. 8. Behavor of the current and the voltage at the output of the converter when ung the HERIC topology. V. COMPARATIVE OSSES ANAYSIS In order to obtan good comparatve loe analy, all three topologe were mulated wth a fxed hytere band current control (Bac H), adaptve hytere band current control (Adaptve H) and proportonal reonant current control (PR Ctrl). Table how the mulaton reult of total wtchng and conducton loe wth an nput power of 65 W (I out Amp) for all three topologe. Fg. 9. Behavor of the current and the voltage at the output of the converter when ung the or HB-ZVR topology. In order to ee that the wtchng frequency almot contant n all three cae, t neceary to obtan the output current harmonc pectrum. Fg. how the harmonc pectrum for the HERIC topology wth and wthout adaptve hytere band. In the other two cae (H5 and HB-ZVR), the current pectrum almot the ame. (a) Topology HERIC H5 HB-ZVR TABE SWITCHING AND CONDUCTION OSSES P n 65W / I out Amp Swtchng Conducton Control oe (W) oe (W) Bac H Adaptve H PR Ctrl Bac H Adaptve H PR Ctrl Bac H Adaptve H PR Ctrl. (b) Fg.. Frequency pectrum of the output current for HERIC topology, (a) Wthout adaptve hytere, (b) Wth adaptve hytere. A can be een n Table, the major loe come from IGBT wtchng procee. Th mean that the wtchng frequency ha an mportant nfluence n the total loe of the ytem. Due th, when the control mplemented wth a fxed hytere band, the loe are major than when an adaptve hytere band current control ytem ued. A hown n Fg. (a), dfferent frequency harmonc appear over a grd perod, th harmonc produce an ncreae of wtchng loe. Table how alo, that conducton loe are almot the ame n each cae. In Table 2 are ummarzed the dtrbuted loe among all emconductor n each topology. It poble to dtnguh that the major loe are located n thoe emconductor whch are wtchng at hgh frequency. In adon t poble to ee the pecfc loe for each emconductor; wth th nformaton, t poble to perform a good thermal degn /9/$ IEEE 76

5 TABE 2 DISTRIBUTION OSSES FOR A THREE TOPOOGIES Semconductor/ P n 65W / I out Amp Total Hytere Topology oe S6 D D2 D3 D4 D Bac HERIC Adaptve PR Ctrl Bac H Adaptve PR Ctrl Bac HB-ZVR Adaptve PR Ctrl. In the cae of H5 topology, the loe are located n. In all three cae the loe behavor almot the ame, the loe are reduced when adaptve hytere band current control and proportonal reonant current control are ued. The effcency n each topology wa obtaned takng nto account the emconductor loe. The Fg. how the reult wth fxed hytere band current control, adaptve hytere band current control and proportonal reonant current control. Effcency (%) Topologe Effcency H5 (Fxed band) H5 (Adaptve Band) HERIC (Fxed Band) HERIC (Adaptve Band) HB-ZVR (Fxed Band) HB-ZVR (Adaptve Band) H5(PR_controller) HERIC(PR_controller) HB-ZVR (PR_controller) Power (W) Fg.. topologe effcency ung fxed hytere band, adaptve hytere band and proportonal reonant current controller. A can be een n Fg., the effcency n each topology when an adaptve hytere current control ued a bt better than when a proportonal reonant current control ued. control and adonally permt an eaer output flter degn due that the wtchng frequency almot contant. On the other hand, wtchng loe can be reduced by ung th adaptve hytere band current control. The analyzed topologe are the more wdely ued n tranformerle ngle-phae ytem (H5 and HERIC). Baed n the prevouly comparatve mulaton reult t can be concluded that n the cae of H5 topology loe are concentrated n. In cae of HERIC topology loe are located among,, and. Fnally n HB-ZVR ngle phae topology, loe are located n. Thee reult mean that n each cae, the loe dtrbuton not the ame and a dfferent thermal degn hould be done. ACKNOWEDGMENT Th reearch work wa upported by the project ENE28-84-C2-/AT from the Spanh Mntry of Scence and Technology (MCYT). REFERENCES []. Malean, P. Mattavell, P. Toman, Hgh Performance Hytere Modulaton Technque for Actve Flter, IEEE Tranacton on Power Electronc, Volume 2, September 997. [2] J. Holtz and S. Stafeld, A Predctve Controller for the Stator Current Vector of AC Machne-fed from a Swtched Voltage Source, n Proc. Int. Power Electronc Conference Rec. (Tokyo), 983, pp [3] M. Cobotaru, R. Teodorecu, and F. Blaabjerg, Control of Sngle-Stage Sngle-Phae Inverter, European Conference on Power Electonc and Applcaton, 25. [4] Y. Hayah, N. Sato, K. Takahah, A Novel Control of a Current- Source Actve Flter for ac Power Sytem Harmonc Compenaton, IEEE Tranacton on Indutral Applcaton, Vol. 27, No. 2, March/Aprl 99. [5] T. Kato, K. Myao, Modfed Hytere Control wth Mnor oop for Sngle-Phae Full-Brdge Inverter, Dohha Unverty, Kyoto Japan, 88CH2565-/88/-689$., 988 IEEE. [6] Bmal K. Boe, An Adaptve Hytere- Band Current Control Technque of a Voltage-Fed PWM Inverter for Machne Drve Sytem, IEEE Tranacton on Idutral Electronc, Vol. 37, No 5, October 99. [7] Maran P. Kazmerkowk, uguu Malean, Current Control Technque for Three-Phae Voltage-Source Converter: A Survey, IEEE Tranacton on Indutral Electronc, Vol. 45, No. 5, October 998. [8] EP A2; Europeche Patentanmeldung, European Patent Offce [9] EP A2; Europeche Patentanmeldung, European Patent Offce [] T. Kereke, G. Vazquez, P. Rodrguez, E. Aldaba, R. Teodorecu, A New Hgh-Effcency Sngle-Phae Tranformerle Inverter Topology, IEEE Tranacton on Idutral Electronc, 29 VI. CONCUSIONS A hytere current control algorthm baed on an adaptve hytere band for ngle phae converter topologe ha been preented n th paper. A t ha been hown analytcally and by mean of mulaton th algorthm permt obtanng a fxed wtchng frequency n all the teted topologe. The man drawback of the conventonal fxed hytere band current control that generate exceve current rpple becaue modulaton frequency vare wthn a band. Th modulaton frequency varaton make complcated the output flter degn. Adaptve hytere band current control keep the good performance of the fxed band hytere current /9/$ IEEE 77