Experimental Evaluation of PWM Control Technique for an NPC Inverter to feed an Asynchronous Machine Using DSP Controller

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1 INTERNATIONA JOURNA OF CIRCUITS, SYSTES AND SIGNA PROCESSING Volume 8, 4 Expeimental Evaluation of PW Contol Technique fo an NPC Invete to feed an Asynchonous achine Using DSP Contolle H. DENOUN, N. BENYAHIA,. ZAOUIA, N. BENAROUCHE, S. HADDAD, S. AIT AAR Abstact This pape discuses modelling and contol of an a neutal point clamped (NPC) invete called thee-level invete witch opeates with the PW switching patten using DSP. The mathematical model of the (NPC) invete is caied out using the convesion and connection functions fo an easie undestanding of the system opeation. Simulation esults using matlab pogam ae epoted in this pape. The pefomance obtained fo the dives of an asynchonous machine fed by this invete ae inteesting. Finally, an analysis and expeimental esults validate the effectiveness of the poposed contol solution. DSP is new geneation of contolle with a main fequency of 5Hz. The speed and the featues of this DSP make it in excellent choice fo the digital contol of an invete. Expeimental esults obtained fom NPC invete and to feed an asynchonous machine will be pesented. Key wods Pulse Width odulation (PW), Total hamonic distotion (THD), Neutal Point Clamping (NPC), ultilevel Invete, Digital Signal Pocesso (DSP), IGBT, atlab simulink, achine asynchonous. I. INTRODUCTION P to now, many studies have been pesented on Umultilevel invetes including many topologies, but the (NPC) invete topology is famous one and attacting many eseaches ove the wold. The thee-level invete (NPC) shown in fig. has been intoduced to enhance the handling capacity of powe electonics using cuently switching devices without any poblematic connections like tansfome o seies connections []. This topology of invete is suitable fo high voltage and high powe invesion because the fowad blocking voltage capability fo giving devices is double and also due to its ability to synthesize wave foms with bette hamonic spectum and low switching fequency []. In this pape, the mathematical model of the NPC invete is done using the convesion and connection function fo an easie undestanding of the system opeation accoding to the possible combination of switching states of the switching device on one leg. The contol technique applied to the NPC invete is studied. This pape pesent also in detail the contol systems of the invete in ode to poduce invete output fo application using Texas Instuments icocontolle (DSP). This wok was suppoted in pat by ATAGE eseach laboatoy, Univesity ouloud ammei, of Tizi-Ouzou, 5 Algeia. Hakim Denoun is with the Electical and Compute Engineeing depatment at ouloud ammei Univesity of Tizi-Ouzou, Algeia, P.O. Box 7, Tizi-Ouzou, Algeia, Tel: ; akim_danoundz@yahoo.f). Naceeddine Benamouche is with the Electical and Compute Engineeing depatment at ouloud ammei Univesity of Tizi-Ouzou, Algeia Univesity, P.O. Box 7, Tizi-Ouzou, Algeia, ( tel : ; benamouchen@yahoo.f). Fig.. Powe cicuit of NPC invete The NPC multilevel invete uses capacitos in seies to divide up the DC bus voltage into diffeent voltage levels. To poduce m-levels in the phase voltage, an m-level NPC invete needs m- capacitos on the de bus. A thee- phase thee-level NPC invete is shown in fig.. The dc bus consists of two capacitos C. Fo a dc bus voltage Uc, the voltage acoss each capacito is Uc/ and each device voltage stess will be limited to one capacito voltage level Uc/ though clamping diodes [3],[4]. II. CONTRO ODE OF A THREE-EVE INVERTER A. Diffeent configuations of the invete To descibe the diffeent sequences of the invete function, let us conside the possible states of the fist leg switches fig.. The thee-level invete has the advantages that the blocking voltage of each switching device is one half of dc-link voltage wheeas full dc-link voltage fo two- level invete. ISSN:

2 INTERNATIONA JOURNA OF CIRCUITS, SYSTES AND SIGNA PROCESSING Volume 8, 4 Howeve, the output phase voltage of the invete can be deduced fom the elation (3) as follow: V A = (V A - V B - V C ) / 3 V B = (V B - V C - V A ) / 3 (4) V C = (V C - V A - V B ) / 3 And these equations can be ewitten using the voltage banches which give : VA FF V B = FF 3 V C F3F3 U CI F3F4 F3F 4 U F33F 34 C (5) Fig.. Diffeent configuations of a leg B. Complementay command We define the complementay contol of the invete leg as follows [5] : BK = BK4 () BK = BK3 It was demonstated [5] that the command given by elationship () is the one which.gives the thee levels Uc, O, -U c, in a optimum way. Table shows the state of the switches and the coesponding output voltage of the invete. Whee V k (k = a, b, c) is the potential of the leg. Table I: Switches states and coesponding voltage B k B k B k3 B k4 V k -Uc Unknown Uc C. odel contol of the thee-level invete - Connection functions It defines the state of the switch. it equals if the switch is ON and if the switch is OFF. The connection functions of the thee-level invete ae elated by the following elation. In most applications, AC machines ae pefeable to DC machines due to thei easy and moe obust constuction without any mechanical switch. DC motos have been used in the high-pefomance domain, with equies fast and pecise toque contol. Howeve, due to the advancement in mico-and powe electonics, highpefomance contol of ac motos can now be implemented at a easonable cost. The vecto contol concept has become a standad tool fo high-pefomance contol us ac motos. The ultimate objective of vecto contol is to enable decoupling contol of toque and flux simila to the contol of a sepaately excited dc moto. In the case of squiel cage induction moto dive systems, the diect and indiect methods of vecto contol have been applied. The diect method equies the difficult task of flux acquisition fo field oientation. The indiect method is basically a fee fowad slip fequency contol scheme that does not equie flux acquisition. Both methods povide decoupling contol of toque and flux. Howeve, the indiect method is gaining populaity due to simplicity of implementation and which is applied in this pape. III. PW STRATEGY AND SIUATION RESUTS The paametes of PW contol technique ae defined as: Amplitude modulation index m a and the fequency atio m f. m a = A m /A c (6) m f = f c / f m (7) Whee A m is the peak amplitude of the contol signal, while A c is the peak amplitude of tiangle signal (caie). m f is the atio between the caie and the contol fequency. The one caie PW thee level invete algoithms is : F k = F k4 F k = F k3 (k =,, 3) () Theefoe, the banch voltages V A, V B,V C ae expessed as follow : V A = F. F. U C F 3. F 4. U c V B = F. F. U C F 3. F 4. U c (3) V C = F 3. F 3. U C F 33. F 34. U c ( U ) B =,B Vef. p = ( V ef. > Up ) etvef. B = B = ( ) ef. > Up etv B = B = V ef. Whee: V ef is called modulating signal U p is the caie signal (8) ISSN:

3 INTERNATIONA JOURNA OF CIRCUITS, SYSTES AND SIGNA PROCESSING Volume 8, 4 Table II: shows the tuth table of the algoithm [5]. A B B B VAB (V) Whee: A = when Vef if not A = B = when Vef > Up if not B = The logical expessions of B and B ae: Time (s) Fig.5. Voltage V AB B = B4 = B A (9) B = B3 = AB The synoptic diagam of the poposed simulation of the stategy is shown in fig. 3 [6], [7]. Coie Absolute Absolute value value Compaato Cicuit The AND B VA (V) Sin wt Absolute value cicuit Compaato Cicuit The NOT opeato The OR opeato B Sin(wt-pi/3)- - Sin(wt-4pi/3)- - e leg 3 e leg -- B -- B -- B3 -- B3 Time (s) Fig.6 Output voltage of phase V A THD(%)=.3587 Fig.3 Synoptic of the poposed PW stategy To illustate the pefomance of the thee-level PW invete, the systems was investigated though compute simulation unde no load. Fig.4, shows the phase voltage at m f =4 and m a =.8 with a sinusoidal tiangle PW and contains hamonics geate which can be easily filteed and the esults ae much bette than conventional two level invete. The compaison of the efeence sinusoidal signal with the tiangula wavefom is done in the PW geneato of the DSP to geneate the contol signals fo the switching devices along with the inveted signals with the equied dead band. By taking the following paametes: R= Ω, =34mH, m f =4, m a =.8. Uc/= 3V, f =5Hz. The obtained simulation esults ae illustated by fig.4, 5, 6, 7, 8. VA h Fig.7 Rang (h) V A hamonic spectum and THD VA Fig.4 Contol pulses fo m f =4 m a =.8 Time (s) Fig.8 Voltage V A ISSN:

4 INTERNATIONA JOURNA OF CIRCUITS, SYSTES AND SIGNA PROCESSING Volume 8, 4 Amplitude (pu) Rs σ s σ ω σ A = R s σs ω σ σ ω σ Rs σs ω σs Rs σ s σst ω σs σt ω σ ω σ s σ st ω σ σt () m a Fig.9 Evolution of the fundamental voltage V A. σs B = σs σ σ s s () THD B. echanical equations Ce = 3/ P p (i d i sq i sq i d ) = 3/ P p (φd i sq - i sd φ q ) (3) m a Fig. THD of voltage V A Fig.4 shows the simulation sequences of uppe-am. Fig.5 shows the line voltage Vab. it has five voltage levels Uc /, Uc /,, - Uc /, Uc /. Fig.6 shows the output voltage of the fist phase of the invete. Fig.7 shows the Va analysis spectal. The voltage spectum shows that the hamonics ae gouped into multiple fequencies centeed aound the fequency switching families. the most impotant hamonics ae numbeed numbe 3 and 5. Fig.8 shows the voltage V A. It shows thee levels of output voltage of an am Uc/,, -Uc/. Fig.9 shows the evolution of the amplitude of the fundamental output voltage V A vesus the ate setting m a. Fig. shows the cuve of the hamonic vesus content in tems of m a. We note that the hamonics deceases as m a inceases. IV. ASYNCHRONE ACHINE ODE AND RESUTS SIUATION A. Electical equations The equations of induction machines ae defined by the state equation as follow: J = dω m f ωm = C e - C (4) dt C. Decoupling contol by compensation Fig. shows the block diagam of a decoupling contol which is govened by the equations (5) and fig. is the block diagam of the indiect field oiented induction moto dive system. The powe supply is chaacteised by a PW voltage souce invete. The moto is contolled accoding to the pincipal of the oientation of the oto flux which is aligned along the d-axis. φ d = φ φ q = V sd = V sld - fem d V sq = V slq fem q With : s R σ s p R ² ( ) V sld = i sd dx = AX BU dt whee X = i i i i sd sq d q ; V U = V sd sq () s R σ s p R ² ( ) V slq = i sq Fem d = ω s σ s i sq Fem q = - ω s σ s i sd - R φ ωs φ ² ²T i sq (5) ISSN:

5 INTERNATIONA JOURNA OF CIRCUITS, SYSTES AND SIGNA PROCESSING Volume 8, 4 I sd ( σ ) I sq ( σ s ) V sld s p Rs R ² V slq p R R ² s Fig. Decoupling contol i sd = i sq = ω sl = φ ( T p Ce 3 Ppφ φ T i sq ) fem d Fem q Vsd V sq Phase voltage VA (V) t(s) Fig.3 phase voltage (V A ) and ω s = ω ω sl To illustate the pefomance of the thee-level PW invete, the systems was investigated though compute simulation unde no load. Fig. shows the phase voltage at m f = and m a =.9 with a sinusoidal tiangle PW and contains hamonics geate which can be easily filteed and the esults ae much bette than conventional two level invete. Fig. shows the speed vaiation at no load. Uc Tee-evel PW Invete PW Contol V A V B V C A Speed w(d/s) ) (d/s) t(s) Fig. 4 speed at no load V. EXPERIENTA TESTS OF THE NPC INVERTER The schematic diagam of the convete cicuit implemented is given in fig.5. It has two pats, the contol cicuit and the powe cicuit. The shaded pat is the contol cicuit containing the DSP contolle TS3F47 that geneates the PW signals and also povides soft stat function [8]. C e φ ω s F.O.C ω sl ω s ƒ V d V q θ s PARK - ω V A V B V C Ω P P φ Ω PI Contolle - Ω Ω ef Fig. Block diagam of the indiect field oiented induction moto dive system fed by thee level PW invete with PI contolle. Fig.5.a DSP TS3F47 implementation diagam ISSN:

A compaison is made of the esults obtained though simulation and expeimental wok unde the same opeating conditions.

6 INTERNATIONA JOURNA OF CIRCUITS, SYSTES AND SIGNA PROCESSING Volume 8, 4 Fig.7 Output voltage of phase VA(5V/Div) Fig.8 Voltage V AB (3V/Div) Fig.5.b Expeimental bench ate on, the thee-level invete was implemented using DSP TS3F47 and its pefomance was studied. A compaison is made of the esults obtained though simulation and expeimental wok unde the same opeating conditions. To veify the theoetical esults obtained on the thee-level invete, we designed and built the vaious cicuits foming the full invete. A powe cicuit fomed by two ams, fomed by twelve tansistos I.G.B.T and eighteen diodes connected in antipaallel. The geneated contol signals wee obtained using seveal contol cads such as conditioning, monitoing, D/A convesion cads. Fig.5 Shows the D.S.P. TS3F47 implementation diagam and expeimental bench. The DSP pogamming was based on the softwae developed by Texas Instuments Code compose. The contol algoithm has been witten in assembly language in ode to optimize the whole tasks of opeation and communication between the DSP, the convete and the oad [] [] [] [3]. Afte the constuction of the vaious cicuits, the theelevel invete was tested in the laboatoy; it functioned as an invete supplying a passive load fomed by a esistance and an inductance. The oscillogaphic esults obtained ae given in fig.6, 7, 8, 9. Fig.6 V A voltage (5V/Div) Fig.9 Contol pulses (v/div) Fo a tiangulo-sinusoidal stategy, a cyclic atio equal to.8 and the index of modulation equals 4 wee taken. Fig.6 clealy shows the V A voltage vaiation. The wavefom of the voltage is simila to that obtained fom the simulation, the diffeence in the zeo level of the voltage that is a little shifted. This is due to the imbalance of the midpoint. Fig.7 shows the change in the voltage of the fist phase V A. Both V A voltage obtained in Pc simulation and expeiments almost the same. The V AB Voltage was pesented in fig.8. Expeimental contol pulses wee shown in fig.9. Both voltages (V A, V A, V AB, B ) of thee level invete obtained in pc simulation and expeiments almost the same. VI. SIUATION AND EXPERIENTA RESUTS OF AN ASYNCHRONOUS ACHINE FEED PW The block diagam of invete feeding asynchonous machine is epesented in fig.. Fo the veification and test of PW modulation cicuits fed asynchonous machine descibed above, a educed powe model has been ealised in eseach lab BT s. Fom INTERNATIONA RECTIFIER (IRGBC4F), powe diode fom THOSON (BYT3PI ) wee used. The load is a thee-phase ISSN:

INTERNATIONA JOURNA OF CIRCUITS, SYSTES AND SIGNA PROCESSING Volume 8, 4 KW asynchonous machine with ated paametes given below: ΔY /38 V 4, 7A /,7 A 83 T / min, 5 Hz.

7 INTERNATIONA JOURNA OF CIRCUITS, SYSTES AND SIGNA PROCESSING Volume 8, 4 KW asynchonous machine with ated paametes given below: ΔY /38 V 4, 7A /,7 A 83 T / min, 5 Hz. The no-load test of asynchonous machine measues the otational losses of the moto and povides infomation. The Invete caie sequence 83 Hz,Ia = A, Uab = 5V. The algoithms ae implemented moe easily by numeical cicuits. The poposed contol cicuits ae shown along with the powe cicuit. The PW is poposed to contol this invete [], [].. Va Exp. 5V/Div Fig. oad voltage Tansfome Ia Sim. Ia Exp. Two ect fies Filte Uc Uc Thee evel Invete PW Contol Cde Fig. Block diagam A. fed PW time [s] A VII. CONCUSION This pape pesents the analysis and design of a digitally contolled invete (NPC) and asynchonous machine fed by this invete based on DSP contol application. DSP TS3lf47 is pogammed to poduce gate pulses by compaing à tiangula caie wave in high fequency and à sinusoidal efeence wave in 5 Hz. Simulation and expeimental esults show the feasibility of such a system. The low commutation fequency of thee-level invetes pemits a ealisation of an optimal contol by elatively simple tools. With a high numbe of semiconductos devices, cuent quality is impoved and weight educed by avoiding heavy cuent filtes. The contol voltage was contolled by micocompute in a much moe sophisticated manne than that descibed hee. This wok open new ways fo futue eseach because the invete can be contolled by numeical signal. The obtained esults ae satisfactoy because the output hamonic components phase ae fewe than those obtained in conventional two-level invetes at the same switching fequency. Expeimental esults using the DSP confim those obtained in numeical simulation. APPENDIX ACHINE PARAETERS A/Div Fig. oad cuent The gaphs pesented in Fig. and Fig. ae showing simulation and expeimental line cuent and phase voltage. The line cuent geneated by thee-level invete has low hamonic components even though the Switching fequency of the active devices is vey low. Va Sim. 5V Rated cuent Rated voltage Rated Powe RatedSpeed R s R s, J F P p 6.4A/3.7A /38V.5Kw 4 ev/mn 4.85Ω 3.85Ω.74Ω 58Ω.3.4 time [s] ISSN:

8 INTERNATIONA JOURNA OF CIRCUITS, SYSTES AND SIGNA PROCESSING Volume 8, 4 PI Contolle paametes P.35 I. NOENCATURE s, suffixes denoting stato and oto, espectively d, q suffixes denoting axes otating synchonously with the oto p diffeential opeato, d / dt s, appaent self inductance pa phase of stato and oto appaent mutual inductance σ R s, R J B P p θ ω s ω ω m ω m m a m f C e leakage facto ( s -²)/ s esistance of stato and oto coils pe phase oto inetia coefficient of fiction numbe of pole pais oto electical angle stato electical fequency oto electical fequency oto mechanical fequency slip fequency modulation index fequency atio (caie to efeence) electomagnetic toque [9] H. Denoun, N.Benamouche, S. haddad, S. eziani and S. Ait ama, A DSP (TS3lf47) Based Implementation of PW fo Single-phase AC-DC Bipola Convete with a Unity Powe Facto,WSEAS Intenational Jounal of Cicuits, Systems and Signal Pocessing, Vol 5,, pp ISSN [] H. Denoun, N.Benamouche, S. haddad, S. eziani and S. Ait ama, A DSP (TS3lf47) Based Implementation of PW fo Single-phase AC-DC Bipola Convete with a Unity Powe Facto, WSEAS Pocceding of the th Intenational Confeence on signal Pocessing, Cobidge, UK Febuay -,, pp-89-95,issn [] C. Panoiu, Baciu,.Panoiu, and C.Cuntan, Simulation esults on the cuents hamonics mitigation on the ailway station line feed using a data acquisition system WSEAS Tans. On Electonics, Vol.4, No., pp.8-36, 7. [] H.Tatizawa, E. S. Netsuo, Calibation of high voltage tansduces fo powe quality measuements, WSEAS Tans. On systems, Vol.8, No, 3, pp [3] I.Ghadbane,. T. Benchouia, Feed back lineaised contol based thee Phase shunt active powe filte, WSEAS Tans. On systems, Vol.7, issue, pp H. Denoun was bon in Algies, Algeia. He eceived the degee in electical engineeing fom the ouloud ammei Univesity, Tizi- Ouzou, Algeia, and the D.E.A degee fom Pais6, and the agiste degee fom Polytechnic School, Algies, Algeia in 998 and espectively, and his PhD in Electical Engineeing fom The Univesity of ouloud ammei Univesity, Tizi-Ouzou, Algeia. He is cuently a senio lectue at the same univesity. His eseach inteests include electical machines and dives, powe electonics and contol systems. REFERENCES [] A.Nebae, A new Neutal-Point Clamped PW Invete, IEEE Tansactions on Industy Applications, Vol.IA-7, N.5, Sept/Oct 98, pp [] P..Bhagwat and V.R.Stefanovic, Genealized Stuctue of a ultilevel PW Invete, IEE, Tansactions on Industy Applications, Vol.IA-9, N.6, Nov/Dec 983, pp [3] Yo- Han ee, Bum-Seok and Dong-Seo Hyun, A Novel PW Scheme fo thee-evel Souce Invete With GTO Thyistos, IEEE Tansactions on Industiel Electonics, Vol.3, N, as/apil, 996. [4] P. Rioual, H. Pouliquen, and J.P.ouis, Regulation of a PW Rectife in the Unbalanced Netwok state using Genealized model, IEEE Tansactions On Powe Electoniocs, Vol., No 3, pp , 996. [5] E.. Bekouk, Contibution à la conduite des machines asynchones monophasées et tiphasées alimentées pa des convetisseus diects et indiects. Application aux gadateus et onduleus multiniveaux. Thèse de doctoat, C.N.A., Pais 996. [6]. Gaad, E.. Bekouk, K. Aliouane, Contibution à la éalisation de la commande d un bas d onduleu à tois niveaux, ème conf, inten su l électotechnique, Oan. [7] H. Denoun, contibution à l étude des convetisseus AC/DC à I à facteu de puissance unitaie, application à la conduite de la machine asynchone. Thèse de agistèe, E..P, Alge. [8] F. Bouchafaa, E..Bekouk and.s.boucheit, Analysis and simulation fo nine-evel voltage souce invetes application to the speed contol of the PS, Elmectomotion, Vol. N 3 July - Septembe 3 pp ISSN:

Modelling and Realisation of a Three - Level P.W.M Inverter Using a D.S.P Controller

INTERNATIONAL JOURNAL OF CIRCUITS, SYSTEMS AND SIGNAL PROCESSING Volume 8, 24 Modelling and Realisation of a Three - Level P.W.M Inverter Using a D.S.P Controller H. DENOUN, N. BENYAHIA, M. ZAOUIA, N.