Hangzhou Dianzi University, School of Mechanical Engineering, China

Transcription

1 Receive for review: Journl of Mechnicl Engineering. All rights reserve. Receive revise form: DOI:1.5545/sv-jme Originl Scientific Pper Accepte for publiction: Dynmic Simultion of Vrible-Spee Vlve-Controlle-Motor Drive System with Power-Assiste Device Xu, M. Ni, J. Chen, G. Ming Xu * Jing Ni Guojin Chen Hngzhou Dinzi University, School of Mechnicl Engineering, Chin The vrible-spee electrohyrulic rive hs been pplie in hyrulic mchines hving power mtching mens. However, further evelopment hs been restricte by its slow response n poor low-spee behvior. Owing to these isvntges, novel rive principle comprising vrible-spee vlve-controlle-motor rive with n ccumultor-bse power ssiste unit (PAU) is propose. The PAU is n energy ssisting n recycling evice, which cn relese or bsorb hyrulic energy ccoring to the system's requirements. With the i of PAU, the propose rive is expecte to improve response n control precision compre with the vrible-spee rive. The propose rive principle system is multi-input-multi-output (MIMO) complicte nonliner system with time-vrying, which increses the control ifficulty. A mthemticl moel of the propose rive ws first erive then hybri control strtegy ws presente. The ynmic simultions of three tritionl rives n the novel one were performe using AMESim-Simulink co-simultion moels. The four rives hve been teste using three common vrible-lo isturbnces. Comprisons of simultion results show tht the propose rive principle system emonstrtes goo ynmic performnce, which cn not only chieve the expecte energy sving trget, but lso significntly improve the response n control precision over the existing vrible-spee rive system. Keywors: vrible-spee, energy sving, vrible-lo, response, hyrulic motor INTRODUCTION The vrible-spee electrohyrulic rive uses vrible-spee electric-motor to rive hyrulic fixe isplcement pump, by justing the electricmotor spee to regulte the hyrulic pump output flow rte so s to meet the lo-emn. It is typicl power mtching hyrulic system. Compre with the conventionl pump-controlle-motor rive principle which uses constnt-spee electric-motor to rive hyrulic vrible isplcement pump, the vriblespee rive cn chieve lrge justble spee-rtio. In ition, the hyrulic fixe isplcement pump hs simpler structure, longer service life n lower noise thn vrible isplcement pump. The frequency converter ws first use to just the electric-motor spee. In recent yers, the servo-motor ws chosen grully to rive the hyrulic fixe isplcement pump. However, the vrible-frequency is still the primry technique for its low price n miniml moifiction to the originl hyrulic system. In the pst twenty yers, the vrible-spee rive hs been wiely stuie to be pplie in hyrulic mchines, such s injection moling mchine, hyrulic elevtor, win turbine, shiel mchine [1] to [3]. Heluser stuie the energy sving performnce of vriblespee rive use in injection moling mchine [4]. Xu iscusse the vrible-spee hyrulic elevtor [5]. Lovrec explore the ppliction possibilities of vrible-spee rive in moling mchine [6]. Ching stuie 2MW win turbine bse on high-power vrible-spee rive technology [7]. However, the vrible-spee rive hs two criticl isvntges, slow response n poor control precision, which resulting from the lrge inerti of the electric-motor [8] n hyrulic pump. In orer to overcome these problems, compoun rive principle (or clle vrible-spee vlve-controlle-ctutor rive) ws built, where proportionl irectionl vlve (or servo irectionl vlve) ws e into the vrible-spee (vrible-frequency) rive system. In the compoun rive system, the frequency converter justs the electric-motor spee to stisfy the ctutor flow-emn n the proportionl irectionl vlve controls the ctutor position or spee. The compoun rive cn improve the control precision n lowspee performnce compre to the vrible-spee rive system [9]. It cn lso improve the ctutor ecelertion process for the short response time of the proportionl irectionl vlve. But it is unble to improve the response when ccelerting [1]. Therefore, it is minly pplie in hyrulic elevtors etc., which o not require fst response [11] to [12]. The vrible-spee electrohyrulic rive with power ssiste unit (PAU) hs been propose in orer to improve responsiveness, especilly when ccelerting. This rive is istinguishe from the compoun rive by the inclusion of PAU. The electric motor-pump cnnot lwys spee up s neee when ccelerting, so the PAU releses energy to improve the ccelertion response. When the ctutor is ecelerting but the electric motor-pump cnnot slow own s neee, the PAU bsorbs energy *Corr. Author s Aress: Hngzhou Dinzi University, School of Mechnicl Engineering, Hngzhou, Chin, [email protected] 581

2 for use in the next working cycle. In other cses, the PAU is turne off. The hyrulic motor is n importnt ctutor in hyrulic system. It ws use mostly in the pumpcontrolle-motor rive system, which normlly respons bly n hs poor control precision. This pper focus on the moeling n ynmic performnce of vrible-spee vlve-controlle-motor rive system with PAU. Three typicl vrible-lo isturbnces were implemente to test the ynmic performnces of the four rive principles, which re the vlve-controlle-motor rive, the vrible-spee pump-controlle-motor rive, the vrible-spee vlve-controlle-motor rive, n the vriblespee vlve-controlle-motor rive with PAU. The purpose is to emonstrte the ynmic performnce of the propose rive principle system compre to the others. 1 PRINCIPLE OF PROPOSED DRIVE Fig. 1 shows the propose rive principle system, where p e, p s inicte the oil pressure of the PAU n of the hyrulic pump outlet respectively. V e, V g, V 1, V 2 inicte the oil-chmber volume of the PAU, the hyrulic pump outlet, the high-pressure n the low-pressure chmber of ctutor respectively. A n m inictes the rotry spee of ctutor, f in is the input frequency of frequency converter, u is the control voltge of proportionl irectionl vlve, u t is the control voltge of proportionl flow vlve, n T L is the lo-torque. There re two power sources, the min power source (the electric motor-pump) n the PAU. The min power source is compose of hyrulic fixe isplcement pump, frequency converter n n electric-motor, where the hyrulic pump is riven by three-phse synchronous electric-motor vi frequency converter. Since the min power source often cnnot meet the flow-emn of hyrulic motor ccelertion, the PAU ws e into the vriblespee vlve-controlle-motor rive system. The PAU is virtully vlve-controlle-ccumultor unit. A bler ccumultor ws chosen s the energy storge element for its fst response, simple structure n low price. The proportionl flow vlve controls the flow rte ssiste or recycle. It cn lso be servo vlve or high-spee on/off vlve. The relief vlve is use s sfety vlve. The PAU is semi-ctive evice, whose ischrging & bsorbing function epens on the pressure ifference between the PAU n hyrulic pump outlet, so the pressures p e n p s shoul be mesure. A hyrulic motor, whose type moel is the sme s the ctutor, is use for loing pump. Different los cn esily be simulte n prouce by setting the crcking pressure of the loing vlve (the proportionl relief vlve in the loing system). As shown in Fig. 1, the min purpose of the proportionl irectionl vlve is to ccelerte the response when ecelerting. The spool-opening of the proportionl irectionl vlve cn be ecrese rpily, thus speeing up the hyrulic motor response when ecelerting. In generl cses, the proportionl irectionl vlve mintins its mximum spool-opening. In ition, the rottionl irection of hyrulic motor cn be conveniently switche by using the proportionl irectionl vlve. Therefore, the hyrulic pump is only neee to rotte towr one irection so s to reuce the impct cuse by switching irections. The four compre rive principle re expline s follows. 1. Vlve-controlle-motor rive. The PAU is close (the flow vlve in the PAU is close). The electric-motor spee mintins 15 r/min continuosly. The proportionl irectionl vlve controls the flow rte inpouring into the hyrulic motor chmber therefore it cn control the spee of the hyrulic motor. The relief vlve works continuosly. 2. Vrible-spee pump-controlle-motor rive. The PAU is close. The spee of hyrulic fixe isplcement pump cn be juste vi the frequency converter. The proportionl irectionl vlve only controls the rottionl irection of hyrulic motor with mximum spool-opening. 3. Vrible-spee vlve-controlle-motor rive. The PAU is close. The proportionl irectionl vlve n the spee-controlle hyrulic pump control the hyrulic motor together. 4. Vrible-spee vlve-controlle-motor rive with PAU. On the bsis of vrible-spee vlvecontrolle-motor rive, the PAU provies for better ccelertion response. When the ctutor is ccelerting but the electric motor-pump cnnot lwys spee up s neee, the PAU releses energy to improve the ccelertion response. When the ctutor is ecelerting but the electric motor-pump cnnot lwys slow own s neee, the PAU bsorbs energy. In other cses, the PAU is turne off. The prmeters of PAU (i.e. ccumultor volume, ccumultor prechrge pressure, etc.) re very importnt to the propose rive system [1]. This pper ims to emonstrte the ynmic performnce 582 Xu, M. Ni, J. Chen, G.

3 Fig. 1. Principle of vrible-spee vlve-controlle-motor rive system with PAU of the propose rive system without generl iscussion of PAU. 2 MATHEMATICAL MODEL In this section, the mthemticl moel of propose rive system is erive. 2.1 Frequency Converter - Electric Motor The frequency converter-electric motor cn be represente by Eq. (1). Kf np = fin, (1) TIMs+1 where n p is the rottionl spee of hyrulic pump, K f is the gin coefficient, T IM is the time coefficient, which increses ccompnie by the increment of the electric motor-pump rottionl inerti. 2.2 Hyrulic Fixe Displcement Pump The flow rte ischrge by hyrulic fixe isplcement pump cn be represente by the Eq. (2). Qp = Dpnp ktcps, (2) where D p is the isplcement of hyrulic fixe isplcement pump, k tc is the lekge coefficient. 2.3 Relief Vlve The propose rive system is power mtching hyrulic system, where the relief vlve is use s sfety vlve. So the mthemticl moel cn be represente by the Eq. (3). K p p p p p r( s cr ) s s cr Qcr =, (3) ps < pcr where K r is the gin coefficient of relief vlve, p cr is the preset crcking pressure of relief vlve. Dynmic Simultion of Vrible-Spee Vlve-Controlle-Motor Drive System with Power-Assiste Device 583

4 2.4 PAU The principle of PAU is shown in Fig. 2. Q p = 5 7 V p p. (8) Since the prmeter p cnnot be etecte in physicl system, we suppose tht p e is equl to p in the ischrging or bsorbing process of ccumultor. Then Eq. (8) cn be represente s: Q p = 5 7 e V 14p e p. (9) Fig. 2. Principle of ccumultor-bse PAU In Fig. 2, p is the pressure of nitrogen gs in the ccumultor, V is the volume of nitrogen gs, Q is the oil flow rte ischrge or bsorbe by the ccumultor, Q e is the oil flow rte ischrge or bsorbe by the PAU, n Q er is the overflowing flow rte by the relief vlve in PAU. The moeling of propose PAU is euce s follows. In the propose rive system, the time require for oil to be ischrge or bsorbe by PAU is very short, so the nitrogen gs in the ccumultor cn be suppose to work in n ibtic process. Eq. (4) cn be estblishe by Boyle's lw. 14. p V = const. (4) The erivtion of Eq. (4) is: 4. V 14. p 14. p V + V =. (5) Then the oil flow rte ischrge by ccumultor cn be erive such tht: n lso Q p V V = =, (6) 14. p p V = const. = p V, (7) where p is the initil pressure of nitrogen gs in the ccumultor, V is the initil volume of nitrogen gs in the ccumultor; both re known. Using Eq. (6) n (7), Eq. (8) cn be euce. The proportionl flow vlve cn be represente by: 2 Qe = C Wt Xvt pe ps sgn( pe ps ), (1) ρ where C is the ischrge coefficient of flow vlve, W t is the spool re grient of flow vlve, X vt is the spool isplcement of flow vlve, ρ is the oil ensity, 1 pe > ps sgn( pe ps) = pe = ps. 1 pe < ps For the flow vlve, the reltionship between the spool isplcement n control voltge cn be simplifie s: X vt Ktv =, (11) u 1 t s + 1 ω where K tv is the gin coefficient of flow vlve n ω t is the nturl frequency of flow vlve. Putting Eq. (11) into Eq. (1), n efining Kt = Ktv C Wt 2/ρ, Eq. (12) cn be euce: Kt Qe = ut pe ps sgn( pe ps ). (12) 1 s + 1 ω t t The relief vlve in PAU cn be represente by: Ker ( pe pec) pe pe pec Qer =, (13) pe < p ec where K er is the gin coefficient of relief vlve, p ec is the crcking pressure of relief vlve. Ignoring the lekge, the flow in the PAU pipeline is represente by Eq. (14): 584 Xu, M. Ni, J. Chen, G.

5 Ve pe Q ( Qe + Qer ) =, (14) E where V e is the oil-tnk volume of PAU (sum of the ccumultor oil-tnk volume n the PAU pipeline volume), n E h is the bulk moulus of hyrulic oil. The relief vlve ws use s sfety vlve in the PAU, which is close uring norml opertion, so Q er cn be suppose to zero. The Eq. (14) cn be simplifie s: Q Q V e pe e =. (15) E The mthemticl moel of the propose PAU cn be escribe by the Eqs. (9), (12) n (15). 3.5 Proportionl Directionl Vlve The irectionl vlve cn be represente s the following linerize eqution: h h QL = KqXv KcpL, (16) where Q L represents the loing flow rte, p L represents the loing pressure, X v represents the spool isplcement of proportionl irectionl vlve, the flow gin coefficient is Kq = QL X v, n the flow-pressure gin coefficient is Kc = QL pl. The reltionship between the spool isplcement n control voltge cn be simplifie s: X v Kv =, (17) u 1 s + 1 ω where D m is the isplcement of hyrulic motor, θ m is the rotry ngle of hyrulic motor, C tm is the lekge coefficient, V t is the totl volume of hyrulic motor, J t is the totl inerti converse to the hyrulic motor shft, B m is the viscous mping coefficient of hyrulic motor, T L is the totl loing torque, T f is the friction torque, n T j is the torque prouce by the hyrulic loing pump. The friction torque T f cn be represente by: Ts nm Tf = =, (21) T sgn( n ) n c where T s is the sttic friction torque n T c is the Coulomb friction torque. T j is the torque prouce by hyrulic loing pump: T = D ( p p ), (22) m j pj j1 j2 where D pj is the isplcement of the hyrulic loing pump n p j1, p j2 represents the pressure of highpressure chmber n low-pressure chmber in the hyrulic loing pump, respectively. 3 SPEED CONTROL STRATEGY Fig. 3 shows the spee-control principle of propose rive system. There re four inputs (n in, n m, p s, p e ) n three outputs (f in, u, u t ). m where K v is the gin coefficient n ω is the nturl frequency of proportionl irectionl vlve. 2.6 Actutor n Loing System The ctutor n loing system cn be represente by the mss conservtion eqution n Newton's secon lw. Q D θm Vt pl L = m + Ctm pl +, (18) 4E D p J 2 θ B m θm = + m + T 2 L, (19) TL = Tf + Tj, (2) m L t h Fig. 3. Spee-control schemtic igrm The spee-control strtegy cn be expline s follows. 1. If n in > n m, the hyrulic motor nees to ccelerte. f in n u shoul be enlrge. If p e > p s, the PAU will be open to relese energy. If p e < p s, the PAU is close. 2. If n in < n m, the hyrulic motor nees to ecelerte. f in n u shoul be reuce. If p e > p s, the PAU is close. If p e < p s, the PAU recovers energy. 3. If n in = n m, the electric-motor mintins its current spee, the proportionl irectionl vlve is use for spee-control. If p e > p s, the PAU is close. If p e < p s, it recovers energy. Dynmic Simultion of Vrible-Spee Vlve-Controlle-Motor Drive System with Power-Assiste Device 585

6 4. If n in is very smll, the electric-motor mintins the llowble minimum spee. The proportionl irectionl vlve is use for spee-control. If p e > p s, the PAU is close. If p e < p s, it recovers energy. The propose rive system is complicte MIMO system couple with strong nonliner n time-vrying prmeters. The hybri control strtegy bse on Proportion-Integrtion-Differentition (PID), which only focuses on system input n output, ws chosen to relize the control strtegy. The etile strtegies of the three controlle-objects re iscusse s below [9] n [13]. 1. Frequency converter The control expression is shown s Eq. (23), where the input-feeforwr plys mjor role in reference trcking, n the PID corrects the error cuse by lo isturbnce. The input rnge of frequency converter is from to 5 Hz. f = min[mx( K n + u( k), ), 5 ], (23) in in in where uk ( ) = k e( k) + λ k ei () + k [() e k e( k 1)], ek ( ) = n ( k) n ( k), fp f fi f = 1 ek ( ) e, k fp, k fi, k f ek ( ) > e in m λ f f represent the PID control prmeters of frequency converter respectively, e f is the integrl seprtion threshol of frequency converter. The prmeter K in equls to the reciprocl of ctutor spee-gin. In vrible-spee rive, the frequency converter controls the spee of hyrulic motor long. If the frequency converter hs n input frequency f in, the hyrulic motor stey-stte spee is n s ccoringly. The hyrulic motor spee-gin is efine s n s / f in. An K in is efine s f in / n s. 2. Proportionl irectionl vlve The control expression is shown s Eq. (24), where the control voltge rnge is from 1 to 1 V. u = min(mx(( k e( k) + λ k ei ( ) + p i + k [() e k e( k 1)]), 1), 1), (24) f k where λ = 1 ek ( ) e, k ek ( ) > e p, k i, k represent the PID control prmeters of proportionl irectionl vlve respectively n e is the integrl seprtion threshol of irectionl vlve. 3. PAU The control expression is shown s Eq. (25). n m is the llowble smllest spee of hyrulic motor, which is etermine by the llowble minimum-spee of electric-motor. k ktp e( k) + λekti ei () + kt [() e k e( k 1)] nin > nm, pe > ps k ktp ek ( ) + λekti e() i + kt [() ek ek ( 1)] nin < nm, pe < ps ut = k, ktp ek ( ) + λek ti e() i + k t [() ek ek ( 1)] n in = n m, p e < p (25) s k ktp e( k) + λ e kti e( i) + kt [ ek ( ) ek ( 1)] nin < nm, pe < ps others ek e where λ e = 1 ( ) e,, k tp, k ti, k t represent the ek ( ) > ee PID control prmeters of PAU respectively, e e is the integrl seprtion threshol of PAU. The propose rive system will increse the control complexity. A lot of control prmeters (shown in Eqs. (23) to (25)) shoul be etermine before simultion. The tuning methos re iscusse in [9]. 4 DYNAMIC SIMULATION Fig. 4 shows the AMESim-Simulink co-simultion moel of propose rive system. In AMESim, lrge set of vlie librries of pre-efine components representing the hyrulic, electric or mechnicl behviour of the system cn employe in creting the system simultion moel [9] n [14]. In the co-simultion, the hyrulic moel is estblishe in AMESim while the control moel is estblishe in Simulink. The co-simultion combines the vntges of the two softwres. As shown in Fig. 4, the simultion moel of loing system is simplifie. Becuse the proportionl irectionl vlve cn switch the rottionl irection of hyrulic motor esily, the loing system is not necessry to switch the lo-torque irection. So the simplifiction of loing system oes not influence the simultion results. The principl prmeters in the simultion moel re shown in Tble 1. To comprehensively stuy the ynmic performnce of propose rive principle system, three typicl vrible-lo isturbnces re implemente: squre-wve vrible lo; fst time-vrying & smll isturbnce vrible lo; slow time-vrying & lrge isturbnce vrible lo. For comprisons, the simultions of the other three rive principle systems re lso stuie. 586 Xu, M. Ni, J. Chen, G.

7 spool-opening without ctutor spee regultion, the overshoot of curve 2 is the lrgest. Curve 3 hs smller overshoot n little justing time thn Curve 2. Curve 4 hs the smllest error in the four rive principle systems (etile comprisons re shown in Tble 2). Fig. 4. AMESim-Simulink co-simultion moel Tble 1. Principl prmeters in simultion moel Prmeter Vlue Prmeter Vlue D p 2 ml/r D m 3 ml/r D pj 3 ml/r T IM 3 K f 3 r/(min Hz) B m.166 Nm/(r/min) J t.1 kgm2 V 6.3 L p 2 MP T s 4.47 Nm p cr 1 MP T f 13.3 Nm E h 7 MP ρ 85 kg/m3 ω 2 Hz ω t 2 Hz Fig. 5. Comprisons of hyrulic motor spee in squre-wve vrible-lo simultions The expression of ech controlle-object in the bove three rive principle systems is the sme s in the propose rive principle system. Corresponingly, the conitions of simultions re the sme, s well s the control prmeters. The reference spee of the hyrulic motor is 6 r/min in ll simultions. In the following texts n figures the numbers 1 to 4 represent the vlve-controlle-motor rive, the vrible-spee pump-controlle-motor rive, the vrible-spee vlve-controlle-motor rive n the propose rive respectively. 4.1 Squre-Wve Vrible-Lo Fig. 5 shows the comprisons of hyrulic spee in the squre-wve vrible-lo simultions, where the squre-wve cycle lsts 1 s. plo is the crcking pressure of loing vlve (the proportionl relief vlve in the loing system). Since the proportionl irectionl vlve in the vrible-spee rive system keeps its mximum Fig. 6. Comprisons of electric-motor spee in squre-wve vrible-lo simultions Fig. 6 shows the comprisons of electric-motor spee in the squre-wve vrible-lo simultions. The electric-motor spee is lwys 15 r/min in the vlve-controlle rive system. Curve 4 hs the smllest chnge in the other three rive systems. Fig. 7 shows the control voltge comprisons of the proportionl irectionl vlve in the squre-wve vrible-lo simultions. The hyrulic power consumptions of systems using four ifferent rive principles re shown in Fig. 8. They re clculte by the Eq. (26): Dynmic Simultion of Vrible-Spee Vlve-Controlle-Motor Drive System with Power-Assiste Device P p Q = s s. (26) 587

8 The hyrulic power require by vlvecontrolle-motor rive system is lwys the lrgest. The hyrulic power of the propose rive system is bsiclly the sme s in the other two rive systems. n 1 2 Where MSE = ( nin ( i) nm ( i)), n is the n numericl vlue of smpling times. 4.2 Fst Time-Vrying & Smll-Disturbnce Vrible-Lo The loing pressure of fst time-vrying & smllisturbnce vrible-lo is represente by: = sin( 2π 1) MP. (27) p lo Fig. 9 shows the comprisons of hyrulic motor spee in the fst time-vrying & smll isturbnce vrible-lo simultions. The error in the system 2 is the lrgest, which even reches to ±4 r/min. The error is bout ±25 r/min in the Curve 1. Curve 4 hs the smllest spee trcking error in the four rive systems. Fig. 7. Comprisons of irectionl vlve control voltge in squrewve vrible-lo simultions Fig. 9. Comprisons of hyrulic motor spee in fst time-vrying & smll-isturbnce vrible-lo simultions Fig. 8. Comprisons of hyrulic power consumptions in squrewve vrible-lo simultions Tble 2 shows the men squre errors (MSE) of hyrulic motor spee trcking n verge hyrulic power consumptions in the squre-wve vrible-lo simultions. It cn be seen tht the propose rive system obtins the best reference-trcking precision on the bsis of energy svings. Tble 2. MSEs n verge hyrulic power consumption in squre-wve vrible-lo simultions System MSE [r 2 /min 2 ] Averge hyrulic power [kw] Fig. 1. Comprisons of electric-motor spee in fst time-vrying & smll-isturbnce vrible-lo simultions Fig. 1 shows the electric-motor spee comprisons in the fst time-vrying & smllisturbnce vrible-lo simultions. Fig. 11 shows 588 Xu, M. Ni, J. Chen, G.

9 the comprisons of hyrulic pump outlet pressure. In Curve 4, there re some big pressure overshoots resulting from the relese of oil by PAU. Fig. 13. Comprisons of hyrulic power consumption in fst timevrying & smll-isturbnce vrible-lo simultions Fig. 11. Comprisons of hyrulic pump outlet pressure in fst time-vrying & smll-isturbnce vrible-lo simultions Tble 3. MSEs n verge hyrulic power consumption in fst time-vrying & smll-isturbnce vrible-lo simultions System MSE [r 2 /min 2 ] Averge hyrulic power [kw] Slow Time-Vrying & Lrge-Disturbnce Vrible-Lo Simultion The slow time-vrying & lrge-isturbnce vriblelo is represente by: p lo = 4+ 2 sin( 2π.) 1 MP. (28) Fig. 12. Comprisons of proportionl irectionl vlve control voltge in fst time-vrying & smll-isturbnce vrible-lo simultions Fig. 14 shows the comprisons of hyrulic motor spee. The spee trcking error in Curve 1 is the biggest, becuse the spool-opening of the irectionl vlve chnges rmticlly so s to suppress the isturbnce. Fig. 12 shows the comprisons of proportionl irectionl vlve control voltge. The control voltge in Curves 3 n 4 ecreses rpily so s to overcome the spee overshoot cuse by isturbnces. Fig. 13 shows the comprisons of hyrulic power consumption. Tble 3 shows the MSEs of hyrulic motor spee trcking n verge hyrulic power consumption. The MSE of the propose rive system is the smllest in the four rive systems while the hyrulic power consumption is only hlf of the vlve-controllemotor rive system. Fig. 14. Comprisons of hyrulic motor spee in slow timevrying & lrge-isturbnce vrible-lo simultions Dynmic Simultion of Vrible-Spee Vlve-Controlle-Motor Drive System with Power-Assiste Device 589

10 Fig. 15 shows the comprisons of irectionl vlve control voltge. An Fig. 16 shows the comprisons of hyrulic pump outlet pressure. Fig. 17. Comprisons of hyrulic power consumption in slow time-vrying & lrge-isturbnce vrible-lo simultions Fig. 15. Comprisons of irectionl vlve control voltge in slow time-vrying & lrge-isturbnce vrible-lo simultions Tble 4. MSEs n verge hyrulic power consumption in slow time-vrying & lrge-isturbnce vrible-lo simultions System MSE [r 2 /min 2 ] Averge hyrulic power [kw] CONCLUSIONS Fig. 16. Comprisons of hyrulic pump outlet pressure in slow time-vrying & lrge-isturbnce vrible-lo simultions Fig. 17 shows the hyrulic power consumptions in the four rive systems. It cn be seen tht the vlve controlle rive system hs the highest power consumption. The hyrulic power consumptions in the other three rive systems re lmost the sme. Tble 4 shows the MSEs of hyrulic motor spee trcking n verge hyrulic power consumption. The MSE in propose rive system is the smllest in the four rive systems while the hyrulic power consumption is bsiclly the sme s tht seen in the vrible-spee rive system n in the vrible-spee vlve-controlle-motor rive system. A vrible-spee vlve-controlle-motor rive system with n ccumultor-bse power-ssiste unit is goo solution for improving the response n control precision of hyrulic motor rives. However, it is complicte non-liner MIMO control system couple with time-vrying tht worsens ynmic performnce. Therefore, PID bse hybri control strtegy is presente. The novel rive principle will increse the cost of the rive system n control complexity, but the cosimultion results show tht it not only chieves the expecte energy svings trget, but lso emonstrtes goo nti-interference performnce. 6 ACKNOWLEDGEMENT This reserch ws supporte by the Ntionl Nturl Science Founion of Chin (Grnt No ), Zhejing province key science n technology innovtion tem (Grnt No. 21R53-3). 7 REFERENCE [1] Ristic, M. (28). Conversnt technology New key spects: Development of vrible spee rives. Proceeings of Interntionl Flui Power Conference, Dresen, p Xu, M. Ni, J. Chen, G.

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