Aances in Engineeing olume 87 n Intenational Confeence on Automation Mechanical an Electical Engineeing (AMEE 7) Reseach on the Composite Baking Contol of Electic Vehicle Jinglei Dou Gaojian Cui Shaosong Li* Shunhang Zheng Xiaoquan Zhu an Zhixin Yu School of Mechatonics Engineeing Changchun Uniesity of Technology Changchun China * Coesponing autho Abstact A new composite baking contol stategy is popose fo a ea-wheel-ie electic ehicle (EV) with both a egeneatie baking system an a hyaulic baking system to achiee impoe baking pefomance an optimal enegy egeneation. Base on the moel peictie contol (MPC) the popose baking contol stategy maintains the slip atio within an optimal ange by ajusting the baking toque continuously besies to ecoe optimal baking enegy a baking toque allocation stategy of maximum egeneation efficiency is esigne. With the contol stategy the egeneatie baking system an the hyaulic baking system wok synchonously to assue high egeneatie efficiency an goo baking pefomance. The popose baking contol stategy is steay an effectie as emonstate by the simulation. Keywos-composite baking; slip atio; electic ehicle (EV); moel peictie contol (MPC); egeneatie baking. I. INTRODUCTION Enegy egeneation uing baking is impotant fo electic ehicle (EV) because it allows the ehicle to impoe its fuel economy an exten its iing ange. Duing baking with the egeneatie system of EV the kinetic enegy is conete to electic enegy so that it can be stoe in an enegy stoage unit such as a battey fo euse when iing. Howee when egeneatie baking is applie to actual ehicles the equie baking foce may not be guaantee because of many constaints[]. theefoe the composite baking of egeneatie baking an hyaulic baking is cucial fo bake comfot an bake safety as well as fo egeneation efficiency. As fo the composite baking few inestigations hae been epote an how to ajust the elationship between egeneatie baking system an hyaulic baking system is still an impotant issue to eseach on EV. Pesent eseach mainly concentates on two iffeent baking scenaios[]. One is the nomal eceleation pocess. Reseach in [] use the sliing-moe contol metho moulating the hyaulic baking foce to obtain the maximum egeneation efficiency an goo bake comfot. A hieachical contol stategy fo coopeatie baking system of an electic ehicle was put fowa in [4] in which the top laye is use to optimize the baking stability base on two sliing moe contol stategies an the bottom laye is use to maximize the egeneatie baking enegy ecoey efficiency with a eallocate baking toque stategy. The othe focus is the emegency baking pocess. To eal with the api eceleation an the altee fiction baking toque a concuence contol an a compensation contol wee popose in [5]. A new baking toque istibution stategy was popose base on the equie baking toque an the egeneatie baking system s status in [6]. Howee these stuies hae limitations in ealing with constaine poblem an can not ealize the optimal baking toque fo each wheel. To achiee the functions aboe this pape eelope a moel peictie contolle to maintain the slip atio within an optimal ange by calculating the optimal baking toque continuously an then esigne a baking toque allocation stategy to ecoe the maximum egeneation enegy. This popose contol stategy can guaantee both the optimal baking toque on each wheel an the maximum egeneation efficiency. The baking effectieness an egeneation efficiency of the popose contol stategy emonstate though the simulation. II. SYSTEM MODEL A. Vehicle Dynamic Moel Consie a ea-wheel-ie ehicle motion when baking opeation is pefome on a at oa. Ignoing the ai esistance an olling esistance assuming no steeing only the longituinal motion is consiee. The ynamic iffeential equations can be expesse as follows. m J (J Fx Fxij Tbij (i ij J pt ) Fxf ij Fxl Fx f j l ) Fxij Tij Tbij (i j l ) () () () whee m is the ehicle mass; is the longituinal elocity; J is the moment of inetia of tie; J pt is the moment of inetia of the powetain which is shae by the two ie wheels; is the wheel angula spee; is the wheel aius; F xij is the fiction foce; an Tij Tbij ae the iing an baking toques. In aition ij fo the font left wheel ij f fo the font ight wheel ij l fo the ea left wheel an ij fo the ea ight wheel. B. Tie Moel The tie moel use in this pape is the Magic Fomula moel eelope by Pacejka. In this moel the tie longituinal foce is escibe as the complex nonlinea function of the longituinal slip atio an tie etical loa. Copyight 7 the Authos. Publishe by Atlantis Pess. This is an open access aticle une the CC BY-NC license (http://ceatiecommons.og/licenses/by-nc/4./). 4
Aances in Engineeing olume 87 C. Longituinal Slip Calculation Moel In this section the longituinal slip atio can be witten as Equation (4). max( ) = (4) whee is a small constant in oe to aoi zeo enominato. In this pape the alue of is set as.. By taking the iffeential of Equation (4) the slip ynamics can be expesse as Equation (5). ( ) (5) D. Moto Moel The powe into the moto can be calculate as Equation (6). P TM (T M ) (6) whee P is the powe geneate by egeneatie baking system; TM is the whole egeneatie baking toque; is the (TM ) enotes the powe wheel angula spee of ea an efficiency. The tansfe function of the electic moto of the fist oe can be witten as G(s).s (7) E. Battey Moel The battey moel is built as an open-cicuit oltage moel. The state of chage (SOC) an moto cuent ae moele as follows t SOC Ib SOCini U I b ( ) (8) Qc P Rb whee SOC is the actual battey SOC alue; SOCini is the initial battey SOC alue; Q c is the total battey enegy capacity. U is the battey open-cicuit oltage; R b is the equialent battey intenal esistant; Ib is the moto cuent. F. Hyaulic Baking Moel The hyaulic system is escibe as pessue inceasing pessue holing an pessue umping pocesses. In this pape we aopt the hyaulic system in [7] III. MPC-BASED COMPOSITE BRAKING CONTROLLER DESIGN In this section a composite baking contol stategy base on MPC is popose. The pimay task of this contolle is to maintain the slip atios within an optimal ange by ajusting the optimal baking toques of fou wheels continuously. The MPC-base contol block iagam is shown as Fig.. whee is the esie alue of MPC slip contolle moule THl TH TMl TM ae the hyaulic an egeneatie baking toques f of l the two ea wheels espectiely ae the fou ties slip atios. an As illustate the MPC slip contolle moule can peict the futue conition of this system an then output the optimize toque comman to the EV moel to ensue that the eal longituinal slip can tack the optimal one. The allocation stategy moule afte the MPC slip moule to allocate the egeneatie baking toque an hyaulic baking toque of composite baking system. A. Refeence Input Fom the Magic Fomula when = the fiction coefficient achiee the maximum an the slip atio is efine as which enotes the slip atio equilibium point. That is to say if slip atio can be kept at all times ieally except fo the timing of slip inceasing fom to until the ehicle stops uing baking the optimal bake pefomance can be achiee. In this ega we choose the slip atio equilibium point as the esie alue.i.e. the efeence input. (9) Rb 5
Aances in Engineeing olume 87 Tb Tbf THl Tbl TMl TH TM Tb f l f l FIGURE I. BLOCK DIAGRAM OF THE MPC-BASED COMPOSITE BRAKING CONTROL SYSTEM. B. MPC Slip Contolle Design Base on the slip contol moel (Equation ()-(5)) of EV a state-space moel fo MPC can be obtaine then a finite imensional optimal contol poblem can be efine [8][9]. Let the state-space moel eie as Equation () x (k ) Ax ( k ) y (k ) C x (k ) y () ]T is efine as the state aiable [Tb Tbf Tbl Tb ]T is efine as the contol input an [ f l ]T is the system output. whee x u Bu ( k ) [ f l The optimization object function of the optimal contol poblem at step k can then be witten as Equation (). Ti ( k P min J y i ( y ( k u i k ) (k i k )) u i u (k i k) i whee ( k i k ) enotes the efeence slip atio of fou wheels; y ( k i k ) enotes the slip atio of fou wheels u(k i k ) is the incement of slip atio; yi ui ae the weighting matices; P an M ae the peictie hoizon an contol hoizon espectiely P M. P y i ( y(k i k ) (k i k )) is to keep the eal i slip atio of each wheel within the optimal one to peent the ties fom locking up. M J u i j k) i (k Tmax j j k) j M P. ; () () i M J FIGURE II. DIAGRAM OF ALLOCATION STRATEGY u (k i k ) is ae to contol the i changing ate of the contol action to pesee the comfot of EV ie. Take the maximum toque limitations an the alue ange of wheel slip into consieation the constains can be expesse as Equation (). MPC soles an optimization poblem online at each time instant with knowlege of the cuent system state aiables an peious system inputs an then takes the fist element of the optimal contol sequence as the cuent contol to the system. C. Baking Toque Allocation Fo ea-wheel-ie EV the baking toques of fou wheels hae been calculate by MPC stategy. The baking toques of font wheels ae supplie by hyaulic system alone an the cuent task is to allocate the ea wheels egeneatie baking toque an hyaulic baking toque. In this ega a new baking toque allocation stategy is esigne fo ea wheel in iew of egeneatie efficiency. The iagam of allocation stategy is shown as Fig.. As illustate this allocation stategy tagets the maximum egeneatie efficiency the egeneatie baking toque is utilize to its maximum extent an the hyaulic baking toque will not be exete on the ea wheel until the moto toque cannot meet the eceleation equest. Theoetically this stategy can maximize the use of the 6
Aances in Engineeing olume 87 achiee the maximum.5 IV. SIMULATION AND ANALYSIS Simulation is conucte in the MATLAB/Simulink enionment to show the contol pefomance of the popose contolle. Accoing to the engineeing stuctue of EV aea-wheel-ie EV moel is built in MATLAB/Simulink. The moel mainly inclues the moto moel the baking moel the battey moel the ie moel the tie moel an the oawheel moel etc. SOC toque In this section the simulation step is efine as.s the peictie hoizon P an the contol hoizon M 5. The oa ahesion coefficient is set to.85 an the initial spee is efine as 78km / h. Velocity(km/h) egeneatie baking egeneation efficiency. Baking toque(nm) 5 font toque ea hyaulic toque ea egeneatie toque (a) Baking toques.4 efeence slip of ea slip of font Slip atio.... (b) Slip atios (c) SOC 8 6 4 () Velocity 4 (e) baking istance FIGURE III. SIMULATION RESULTS OF PROPOSED CONTROLLER. Speaking of the elocity at the beginning of the baking poceue elocity eceases slowly an then it eclines makely. The baking istance ascens gently an finally eaches.5m. V. 5.5 Baking istance(m) Fom the simulation esults of popose contolle shown in Fig. the font baking toque has a fast incease at the fist.5s. As fo the ea wheel at the beginning of the baking poceue the egeneatie baking toque inceases smoothly while the hyaulic baking has a shot oscillation. Afte the egeneatie baking toque inceases to its maximum extent at about.5s which can meet most of the ea baking eman an the ea hyaulic baking toque is kept at a low alue. As can be seen fom Fig. (b) at the beginning of the baking poceue the slip atios incease apily an hae a mall uctuation because of the the shaply inceasing baking toque. Duing this time ue to the big loa of font wheel an the fast esponse of egeneatie system of ea wheel the font slip atio oscillates seeely. The slip atios tace the efeence slip atio well at the est time an ecease to zeo finally. Owning to the maximum supply of egeneatie baking system the SOC alue inceases quickly an almost eache the alue.5..5 CONCLUSION In this pape a new composite baking contol stategy is popose to achiee the optimal baking toques an high egeneation efficiency. This popose contolle takes aantage of MPC to maintain the slip atio within an optimal ange by ajusting the baking toque continuously an a baking toque allocation stategy is esigne in iew of the egeneation efficiency. The effectieness of the popose contol system has been eifie though simulation using an EV moel which was built in Simulink. The esults poe that this popose contolle can stop the ehicle fom locking up an implement goo baking efficiency meanwhile the maximum egeneation efficiency can be achiee. ACKNOWLEDGMENT The wok is suppote by the Jilin Poince Science an Technology Foun fo Young Scholas (7597JH; No.656JH) by Key Technology on Majo pogam of Jilin Poince (75GX) an by the Ministy of Eucation "Chunhui Plan" (Z6). 7
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