Control of Single-Phase Four-Quadrant PWM Rectifier for Traction Systems

Transcription

1 Control of ngle-phase Four-Quadrant Rectfer for Tracton ystems 17th Int. Conference on Electrcal Drves and Power Electroncs The Hgh Tatras, lovaka 8 3 eptember, 11 ubomr Grman, Martn Hrasko, Jozef Kuchta, Jozef Buday Electrotechncal Research and Projectng Company, j.s.c. Trencanska 19, K Nova Dubnca, lovaka Tel.: +41()4/44963, Fax. +41()4/4434 grman@evpu.sk, hrasko@evpu.sk, kuchta@evpu.sk, buday@evpu.sk Abstract Ths research has been motvated by ndustral demand for a sngle phase four-uadrant rectfer for tracton systems. Ths paper presents an advanced control structure desgn for a sngle phase rectfer. The control structure conssts of a proportonal-resonant controller usng a fast phase angle and freuency estmator. The estmaton algorthm s derved from the weghted least-suares estmaton method. The feasblty of the proposed control structure s confrmed by expermental tests performed on desgned laboratory prototype. Keywords rectfer, converter control,, resonant control, phase angle estmaton, tracton applcaton I. INTRODUCTION At the begnnng of the 197 s, the research and development of electrc tracton schemes of an electrc locomotve wth the tracton voltage 15kV/16,7Hz (Germany, wtzerland, Austra, weden, Norway) and 5kV/5Hz (France, pan, etc.) has been orented almost exclusvely to mplementaton of a three-phase nducton motor as an electrc tracton motor whch had replace a contact DC tracton motor wth seres and separate exctaton. Gradually, the tracton AC sngle-phase voltage has been reduced by a tracton vehcle transformer wth voltage transfer whch allows to generate a DC-lnk voltage for tracton freuency converters to supply the three-phase nducton tracton motor (ITM) wth nomnal lne-to-lne voltage (approx. -.kv). The margnal power of ITM drected to hundreds kw, today the top locomotves has power about MW. Use ths power wth four or sx ITM n one vehcle reures that from tracton lne was consumed power wth the power factor nearng to unty and mnmal dstorton of the tracton voltage. After extensve research and verfcaton, t came to the concluson that mpulse rectfer referred to as four-uadrant converter s connected to secondary wndng of the tracton transformer. The power part of converter the most freuently conssts the sngle-phase brdge lke other converters makes t possble to transmsson of electrcty between AC and DC tracton system DC-lnk of tracton freuency converters n both drectons. Whereas dmenson of the mpulse 4Qconverter s pretty smple, the problem appears the control structure n all operatng condtons of the vehcle for achevng the power factor nearng to unty. These ssues and possble solutons are descrbed n ths paper. In a sngle phase system, the reference of the lne current s a 5 Hz AC sgnal under the steady state, and the current controller s reured to track such an AC reference. There have been several control schemes for an AC trackng controller such as the hysteress control methods, the predctve control methods, and so on [], [14]. In ths work s used the resonant control approach [4], [7-1] for an AC trackng controller. The proposed control scheme usng the PR (Proportonal-Resonant) controller that s capable of trackng a snusodal lne current reference wthout an addtonal predcton or an extremely hgh control gan. When electrcal ralway tracton crosses over to the power secton suppled by another voltage source, the ampltude and/or the phase angle of a source voltage may change n a step manner. In ths case, the normal phase angle detector, such as a phase locked loop (P) and a lowpass (or notch) flter, typcally generates a phase delay, results n a sluggsh response, and causes some tme crtcal machne to malfuncton. In ths work, a source voltage estmator s used based on the weghted least suares estmaton (WE) method [9]. The proposed estmator provdes the phase angle, the freuency, and the magntude nformaton of the source voltage s fundamental component wthout a delay. rectfer The rectfer controlled by pulse wdth modulaton () consumes current of reured shape, whch s mostly snusodal. It works wth a gven phase dsplacement between the consumed current and the supply voltage. The power factor can also be controlled and there are mnmal effects on the supply network. The man features of rectfers are [5]: b-drectonal power flow, nearly snusodal nput current, regulaton of nput power factor to unty, low harmonc dstorton of lne current (THD below 5%), adjustment and stablzaton of DC lnk voltage (or current), reduced capactor (or nductor) sze due to the contnuous current, properly operated under lne voltage dstorton and lne freuency varatons.

2 rectfers can be dvded nto two groups accordng to power crcut connecton [1]: voltage rectfers (called boost rectfer ncreases voltage): reures hgher voltage on the DC sde than the maxmum value of the supply voltage. The rectfed voltage on the output s smoother than the output voltage of the current type rectfer. They also reure a more powerful mcroprocessor for ther control. Output voltage lower than the voltage on nput sde can be obtaned only wth ncreased reactve power consumpton. current rectfers (called buck rectfer decreases voltage): the maxmum value of the supply voltage must be hgher than the value of the rectfed voltage. The man advantage s that the rectfed voltage s regulated from zero. They are sutable for work wth DC loads (DC motors, current nverters). The sngle phase rectfer conssts of 4 IGBTs connected n full brdge [1] s shown n Fg. 1. 5kV 5Hz M U P Tr Fgure 1. tructure of a sngle phase rectfer The source power s suppled through a transformer Tr and the nput nductance. The output DC lnk voltage s fltered by capactor C and fed nto a 3-phase nverter that drves the tracton. uppled voltage and the voltage at the rectfer nput are snusodal waveforms separated by the nput nductance. Therefore the energy flow depends on the angle between these two phases. ee the phase dagram n Fg. a [1], [5], [11]. δ rectfer 1 4 δ X 3 Fgure. Phase dagrams The power transferred from the supply to the nput termnals of the rectfer s: ϕ a) I DC + C X b) c) δ Tracton nverter X M U R P = snδ = cosφ (1) X where s RM value of nput supply voltage, RM value of frst harmoncs consumed by AC rectfer nput, δ phase dsplacement between phasors a (deg), X nput nductor reactance at 5Hz (Ω ), φ power factor. In order to make the rectfed voltage constant the nput and output powers must be balanced. Then as the phasor dagram n Fg. a shows: I I snδ cos φ =, () X U R cosδ snφ =. (3) X As long as the reactve power consumed s eual to zero the power factor s eual to unty. Therefore () and (3) can be adapted to: X = snδ, (4) = cosδ. (5) Phasor dagrams of the rectfer whch works both as a rectfer and as an nverter are shown n Fgs. b and c. The am s to control the rectfer n such a way that t consumes harmoncal current from the supply network whch s n phase wth the supply voltage. Ths can be acheved by controllng the rectfer by pulse wdth modulaton. II. PROPOED CONTRO AND ETIMATION AGORITHM A. Phase angle and freuency estmaton The phase angle of a source voltage s used to calculate and control the flow of actve/reactve power. The phase angle s a crtcal pece of nformaton for the operaton of most power condtonng eupment, such as pulse wdth modulaton AC/DC converter, unnterruptble power supples (UP), AC voltage compensators, statc VAR compensators (VC), actve harmonc flters etc. In power condtonng eupment, the exact value of a postve seuence s needed to acheve the unty power factor and constant output voltage, whereas the exact value of a negatve seuence s needed for unbalance compensaton. A fast phase angle and freuency estmator s presented, whch s capable of estmatng the phase angle and the freuency of the source voltage even under a hghly dstorted source voltage condton or sudden ampltude, phase angle, or

3 freuency changng condton. The algorthm s derved from the weghted least suares estmaton (WE) [8-1]. A sngle phase voltage s expressed such that U ( t) n( ωt + ϕ) = n( ωt) + U cos( ωt) =, (6) m where U m s ampltude of source voltage, ω constant angular freuency (rad/s), ϕ phase angle (deg), U d = U m cos( ϕ), U = U m sn( ϕ). By applyng the WE method to (6), the estmaton Uˆ are obtaned from such that ( t ) xˆ ( t ) + R( t )( U ( t ) H( t ) x( t )) = 1 ˆ 1 d Uˆ d and x ˆ, = 1,,3, K (7) [ ] T where xˆ ( t ) = U d ( t ) U ( t ), ( t ) = [ sn( ωt ) cos( ωt )] H, T ( t ) = P( t 1) H( t ) 1 + H( t ) P( t 1 ) H( t ) 1 P( t ) = λ ( P( t 1 ) R( t ) H( t ) P( t 1 )), (, 1) x ˆ ( t ) =, ( ) P t = γ I R, T ( ) 1 R, λ s the forgettng factor, ntal condtons: γ > s the ntal covarance constant. The nose mmunty of the WE estmator can be ncreased by selectng a larger forgettng factor λ and faster convergence can be acheved by choosng the larger γ. The phase angles estmaton s obtaned from Uˆ d and Uˆ such that ( ) ( t ) Uˆ ( t ), Uˆ ( t ) ˆ ϕ = atan, = 1,,3, K (8) d where atan s the arc-tangent functon. The freuency nformaton s ute mportant for phase angle estmaton algorthm. The phase angle estmaton algorthm can be extended to the estmaton of ω, when the freuency vares. When the freuency estmate ωˆ s not eual to the real freuency ω the estmated phase angle ϕ vares such that ( t ) ˆ ϕ( t ) = ( ω ω)( t t ) 1 ˆ ˆ ϕ = ˆ ϕ, = 1,,3, K (9) 1 We can recognze that f ϕ ˆ, then there s a freuency estmaton error. The basc dea for updatng ωˆ s to employ a PI controller (1) so that ϕˆ s nullfed ( t ) = ˆ ω( t ) + K Pf e( t ) + K If e( t j ) ˆ ω, = 1,,3, K (1) j= where e( t ) ˆ( t ) ˆ ϕ( t ) = 1 ϕ s error, K Pf proportonal gan, K If ntegral gan. The estmated source voltage Uˆ s then obtaned as ( t ) Uˆ ( t ) sn( ˆ ωt ) Uˆ ( t ) cos( ˆ ωt ) U ˆ = +, = 1,,3, K (11) d B. Voltage and current controller The proposed control system conssts of the DC-lnk voltage controller, the current controller, the phase angle estmator and the generator [7], [9], see the structure n Fg. 3. The DC-lnk voltage controller s mplemented by usng a conventonal proportonal-ntegral (PI) controller whose output s the ampltude of the current reference I m and transfer functon s gven by G ( s) K Iu = K Pu, (1) s PI + where K Pu and K Ru are the proportonal and the ntegral control gan, respectvely. The current reference I * s s constructed by multplyng the synchronzed sgnal wth the source voltage: * I s = I m sn( ˆ ω t + ϕ). The snusodal current reference I * s s fed nto the current controller. The current controller s constructed based on the proportonal-resonant (PR) controller whose transfer functon [4] s gven by K Rs GPR ( s) = K P +, (13) s + ω where K P and K R are the proportonal and the resonant control gan, respectvely, ω s fundamental angular freuency of the source current (rad/s). U * DC 3f AM M PI controller I m Inverter Phase angle and freuency estmator ( ˆt ω + ϕ) sn ωˆ I * s I s + Fgure 3. Control structure of a sngle phase rectfer C PR controller Rectfer U pwm

4 The tme doman response of the resonant controller when K P =.5, K R =, f = 5Hz wth snusodal nput sn(ωt) s shown n Fg Input Output III. EXPERIMENTA REUT The control structure of a sngle phase rectfer has been confrmed by expermental tests performed on desgned laboratory prototype. Block dagram of the rectfer control system s shown n Fg. 5. The power part s realzed by four IGBT transstors and the dgtal sgnal processor TM3F8335 (Texas Instruments) was chosen as controller and for computng WE algorthm. y -.5 Rectfer + C Inverter M Fgure 4: Tme doman response of the PR controller It can be seen from Fg. 4 that the gan of the transfer functon (13) s nfnty at ω, the output s n phase wth the nput sgnal, but the ampltude s amplfed wth tme. Wth the resonant control method, one can track the hgh freuency snusodal current reference wthout ncreasng the swtchng freuency nor adoptng an extremely large control gan. For proper operaton of rectfer a mnmum DC-lnk voltage s reured [1], [3], [5]. Generally, t can be determned by the maxmum value of the supply voltage that s U > U or mn > ( RM). (14) DC mn max If ths condton s not fulflled, the full control of the nput current s not possble. Defnng the natural DC-lnk voltage value (as t s possble to obtan n case of not operatng transstors) the freewheelng dodes consttute a standard dode brdge. Typcally, the reference value for the controlled DC-lnk voltage should be chosen about 1% above the natural DC-lnk voltage. The unty power factor reured for rectfer operaton can be obtaned n case of R U = U + U. (15) The voltage drop across the nductor U depends on reactance of the nductor at the nput freuency and on the nput current. The magntude of the swtchng voltage vectors depends on the DC-lnk voltage level. The nductor has to be desgned carefully because low nductance wll gve a hgh current rpple and wll make the desgn more dependng on the lne mpedance. The hgh value of nductance wll gve a low current rpple, but smultaneously reduces the operaton range of the rectfer. A hgh current (hgh power) through the nductance reures ether a hgh DC-lnk voltage or a low nductance (low mpedance) [5]. ynchronzaton Control card TM3F8335 Fgure 5: mplfed block dagram of the rectfer In order to keep proper functon of control algorthm, t s necessary to synchronze the control structure wth power grd voltage curve. When supposng purely snusodal voltage curve, we only need to know the moments when the voltage curve crosses the zero axes (moments of polarty change) and the voltage polarty n every half-perod. The easest way to follow ths condton s to convert snusodal curve (power grd voltage) nto the suare shape wth logcal levels of and 3V, otherwse log. and log. 1 as well. og. corresponds to negatve half-wave, log. 1 to postve. gnal edges ndcate the zero crossngs. The DP processor these zero crossng by means of external nterrupt. The polarty s evaluated from the zero crossng drecton rsng or fallng edge [6]. Experments were performed wth the parameters of controllers gven n Table 1. The swtchng freuency was set to be 5kHz and the parameters of the phase angle estmator were selected such that λ =.999 and γ =. TABE I: IT OF THE PARAMETER OF THE CONTROER Parameters of the controllers I 1,,3 ω freuency voltage current K Pf 1 K Pu 1.5 K P 3 K If 5 K Iu.5 K R 6 The condtons for test were: m = 35V, = 3V, the nput nductor = 35mH, the DC lnk capactor C = 3µF. The parameters of nducton motor were: P n = 7.5kW, U n = 38V, f = 5Hz, n = 15rpm and number of poles p = 4. The expermental tests of a sngle phase rectfer has been performed by nducton motor (IM) wth motor and

5 generator (recuperaton) operaton modes. The recuperaton has been realzed by the commutaton dynamometer wth parameters P n = 41kW, U n = 38V, I n = 145A, f = 5Hz, n = 8rpm. The results of expermental tests are shown n the followng fgures., *I s *I s -fdb -ref Fgure 6: Transent responses when DC-lnk voltage changes gradually, 5*I s cos(φ), 1*I s cos(φ) *I s -fdb -ref Fgure 7: Transent responses (motor mode): load on M z = 16Nm (nput voltage, current, DC-lnk voltage and power factor) *I s -fdb -ref Fgure 8: Transent responses (generator mode): load on M z = 16Nm (nput voltage, current, DC-lnk voltage and power factor), 5*I s cos(φ) fdb -ref Fgure 9: Transent responses (motor mode generator mode): (nput voltage, current, DC-lnk voltage and power factor) Fg. 6 shows the expermental results of transent responses ( rectfer) when DC-lnk voltage changes gradually and no-load s attached. The nput current surge s reduced by the ramp of reference value of DC-lnk voltage. The reured value s reached n tme.6s. The results of transent responses rectfer and nverter n motor mode when IM has load on M z = 16Nm s shown n Fg. 7. In ths case the voltage s n the phase wth the current (the value of power factor s.994) and rpple of DC-lnk voltage s ±.3V. Fg. 8 shows the expermental results of transent responses ( rectfer and nverter) n recuperaton (generator) mode when IM has load on M z = 16Nm. The voltage s n phase opposton wth the current (the value of power factor s -.995) and rpple of DC-lnk voltage s ±.6V. Fg. 9 shows the last results of transent responses when operaton mode s changed (motor generator) n tme.8s. Rse of DC-lnk voltage s about.3% (7V) from reference value (3V). IV. CONCUION Ths paper presented an advanced control structure desgn for a sngle phase rectfer. The control structure conssts of a proportonal-resonant controller usng a fast phase angle and freuency estmator. The estmaton algorthm s derved from the weghted least-suares estmaton method. The rectfer can perform well n many applcatons, for example as an actve flter or as an nput rectfer for an ndrect freuency converter. Ths applcaton s useful manly n tracton, where the AC voltage from the trolley wre s frst rectfed, and the tracton nverters and also other auxlary converters are fed from the output of the rectfer. A tracton vehcle eupped wth a rectfer does not consume reactve power, wll not load the supply network wth harmoncs and can recuperate. The proposed control structure s confrmed by expermental tests performed on desgned laboratory prototype.

6 ACKNOWEDGMENT Ths work was supported by the lovak Research and Development Agency under the contract No. APVV-53-7 and OPVaV-678. REFERENCE [1] J. Bauer, ngle-phase Pulse Wdth Modulated Rectfer, Acta Polytechnca, vol. 48, no. 3, 8, pp [] M. Cchowlas, M. Kazmerkowsk, Comparson of Current Control Technues for Rectfers, IIE 1, l'aula, Wlochy. [3] J. Javurek, M. Kopecky, Pulse Rectfer: Input Crcut of Three-ystems ocomotve, AT&P journal, no., 5, pp [n Czech]. [4] A. Kulka, T. Undeland,. Vazuez,. G. Franuelo, tatonary Frame Voltage Harmonc Controller for tandalo Power Generaton EPE 7 Conference Alborg, Danmark, 7. [5] J. ettle, R. Dolecek, EMC Increasng of Rectfer n Comparson wth Classcal Rectfer, Radoengneerng, vol 17, no. 4, 8, pp [6] J. Mchalk, J. Molnar, Z. Peroutka, ngle Phase Current-ource Actve Rectfer for Tracton: Control ystem Desgn and Practcal Problems, 6th Internatonal Conference EEKTRO 6, Zlna, lovaka, May 3-4, 6. [7] Y. ato, T. Ishzuka, K. Nezu, T. Kataoka, A New Control trategy for Voltage-Type Rectfers to Realze Zero teady-tate Control Error n Input Current, IEEE Transactons on Industry Applcatons, vol. 34, no. 3, 1998, pp [8] H.. ong, R. Kel, P. Mutschler, J. Weem, K. Nam, Advanced Control cheme for a ngle-phase Rectfer n Tracton Applcaton, IEEE Industry Applcaton Conference, 3, pp [9] H.. ong, K. Nam, Instantaneous Phase-Angle Estmaton Algorthm under Unbalanced Voltage-ag Condtons, IEE Proceedngs Generaton, Transmsson & Dstrbuton, vol. 147, no. 6,, pp [1] H.. ong, K. Nam, P. Mutschler, Very Fast Phase Angle Estmaton Algorthm for a ngle-phase ystem havng udden Phase Angle Jumps, IEEE Industry Applcaton Conference,, pp [11] K. Thyagarajah, V.T. Ranganathan, B.. Ramakrshna Iyengar, A Hgh wtchng Freuency IGBT Rectfed Inverter ystem for AC Motor Drves Operatng from ngle Phase upply, IEEE Transactons on Power Electroncs, vol. 6, no. 4, [1] V. Venkatesh,. Rao, B.. Gupta, V.T. Ranganathan, ngle Phase Front End Converter for Tracton Drve, IE(I) Journal-E, vol. 87, 6. THE AUTHOR Ľubomír Grman (Ing., PhD.) was born n Topolcany, lovaka, n He graduated from the Faculty of Electrcal Engneerng and Informaton Technology, lovak Unversty of Technology, Bratslava, n. He receved PhD degree n Automaton and Control at the same unversty, n 5. He worked as research worker at Insttute of Control and Industral Informatcs from 5 to 7. At present he s a research and development engneer at Electrotechncal Research and Projectng Company n Nova Dubnca, lovaka. The man feld of hs research and actvtes are control structure desgn and ther mplementaton to dgtal sgnal processors. Martn HRAŠKO (Ing., PhD.) was born n He receved PhD. degree (6) n power electroncs, specalzatons electrc drves from the Unversty of Zlna. nce graduatng, he has worked as R&D engneer of control systems n Electrotechncal Research and Projectng Company (EVPU j.s.c), Nova Dubnca, lovaka. Hs research nterests nclude electrc drves, power electroncs and dgtal control. Jozef Kuchta (Assoc. Prof., Ing., PhD.) was born n He receved PhD. degree from the Faculty of Electrcal Engneerng, lovak Techncal Unversty, n He was apponted Assocate Professor n the feld of Power Electrcal Engneerng at the Faculty of Electrcal Engneerng, Unversty of Žlna (EF ŽU), n 8. From 1971 he worked as assstant professor at the EF ŽU n Žlna and from 1977 as leader of research n the feld of Electrcal Machnes and Drves n Electrotechncal Research and Projectng Company (EVPÚ j.s.c). Hs man research nterests are specal electrc machnes, a new magnetc materals and components of advanced electrc and desel-electrc locomotves. Jozef Buday (Assoc. Prof., Ing., PhD.) was born n He receved PhD. degree from the Faculty of Electrcal Engneerng, Unversty of Žlna, n He was apponted Assocate Professor at the same faculty, n 6. He worked n the feld of power electroncs, automaton and mechatroncs. At present he s managng drector and R&D department manager n Electrotechncal Research and Projectng Company (EVPÚ j.s.c). He s laureate of many awards at home and abroad for buldng of testng laboratores, member of several commssons n department and government level.