Design of an electrical drive for motorized bicycles

Transcription

1 Design of an eletial dive fo motoized biyles C. Boaletti, G. Duni, P. Petui, E. Santini Depatment of Eletial Engineeing Univesity of Rome "La Sapienza" Via Eudossiana 18, Rome, Italy Tel , Fax Abstat. The aim of this wok is the design of an eletial dive fo a motoized biyle, haateised by new solutions fo the ontol method and the egeneative baking system. A dynami model of the vehile has been ealised, and the haateistis of the dive have been individuated. An effetive losed-loop ontol stategy has been studied, adjusting the moto toque and the uent in ode to inease the availability ange. Finally, a feasibility study of a egeneative baking system based on the supeapaito tehnology has been aied out. All the omponents of the dive have been seleted among the models available on the maket. In the pape the esults of the simulations ae pesented and othe tehnial-eonomial aspets suh as enegy onsumption and osts ae also biefly disussed. Key wods Powe-assisted biyle, adial flux pemanent magnet DC moto, supeapaitos, egeneative powe ontol 1. Intodution Human-poweed hybid eleti vehiles an beome a key to pesonal tanspotation in an envionment whee atmosphei pollution must be limited, whee automotive taffi ongestion is sevee, and whee paking spae in uban entes is not available [1]. Aoding to the Euopean Law 2002/24/CE item h point 1, a powe-assisted biyle is a two o thee wheels vehile equipped with an auxiliay eleti moto whose maximum nominal powe is 0.25 kw. Eletial biyles offe extemely effiient, pollutionfee tanspotation fo uban and sububan aeas, and the addition of eleti dive extends thei ange. Motoized biyles ae an eonomi and eologial vehile suitable fo all ages; the use of a helmet is not ompulsoy; they will not nomally equie egistation and taxes, liensing o opeato qualifiation [2, 3]. In this pape, the tem motoized biyle is used to desibe a patially moto poweed biyle, ommonly known as pedele (Pedal eleti yle) [3]. The moto ation is pogessively edued and finally inteupted if a 25 km/h speed is eahed (suh speed limit is imposed fo seuity eason, if the ylist stops pedalling o if the bake is used. Pedalling is the main fom of populsion, while the moto gives exta speed, espeially uphill. The eletial dive onsists of fou main omponents: 1) a moto 2) a powe tansmission system 3) a ontol system 4) a battey pak The battey pak and thus the vehile autonomy is the main aspet to be foused on. In this sense, a losed loop ontol iuit fo the output powe ontol has been studied to be implemented in the eletial dive, avoiding undesied aeleations and ineasing the battey ange. Suh a solution is not ommeially available. The eoveing of the baking enegy by means of the supeapaito tehnology an detemine a edution of the eletomagneti stesses on the battey pak, and theefoe a longe battey life. 2. Eletial Dive Design The powe popelling a biyle and ide goes mostly into oveoming wind esistane and lifting mass up hills at nomal biyle speeds [2, 3]. Beaing and tie fition ae small but an equal wind esistane at vey low speeds. The eleti moto toque uve is a funtion of oad slope p, olling fition oeffiient C oll (whose value depends on the oad ondition, wind speed V w, ylist esistane oeffiient C, and total mass m of the biyleylist system. Equation (1) epesents the equilibium and equation (2) keeps the bluff body pessue dag and skin fition dag into aount. T T + T + T C tot ai (1) ai C slope A ρ 2 fition 2 ( V + V ) b Expeimental elaboations have been pefomed to estimate the total toque vaiation in funtion of speed with thee standad slope gades: 1%, 10% and 12%. Fig. 1 shows that, moving fom a flat oad to a limb, the total equested toque passes fom 2.17 Nm to Nm, W (2) RE&PQJ, Vol. 1, No.6, Mah 2008

2 fo a 7.2 km/h speed. Fig. 2 shows the influene of the total mass of the system on the equied powe. Povided that the ylist is pedalling, the above mentioned law does not fix any onstaint on the level of the assistane. Howeve it stongly affets the battey autonomy. the ontol system will egulate the voltage so to obtain the oet uent and toque value. Suh a losed loop ontol system is not available on the pedele maket. This kind of egulations also allows estimating the battey state of hage and opeating to impove the battey autonomy. A onstant value of phase uent is imposed; suh value emains onstant until a speed value n n is eahed. It is possible to estimate the eletial powe equied by the moto. Fo the pesent ase a limit P n 250 W is fixed by the law, oesponding to speed n n. Theefoe, the opeation is limited by a uve in whih eletomagneti toque and speed hange in a way that the powe absobed by the moto is onstant (see Fig. 3). Toque Fig Slope influene on the total toque fo a 80kg ylist Toque (Nm) Toque 3 8, Speed (Km/h) Fig Opeating limit fo the DC bushless mahine 4. Contol System The ombination between the ylist musola powe and the powe of the moto ae optimised by means of a speifi ontol system that an manage the powe inputs in the diffeent load onditions. The basi onfiguation fo a pedele an be epesented by the following sheme (Fig. 4) in whih the powe flows ae shown [3]. Fig Mass influene on the total equied powe 3. Choie of the Eleti Moto Two diffeent types of motos ae ommonly hosen fo the auxiliay dive of suh vehiles: DC Bushed motos and adial flux DC Bushless motos with pemanent magnets (RFPM). Mostly fo its edued size and highe effiieny a DC Bushless moto with a patiula shape a so-alled hub moto - has been hosen (extenal oto and intenal stato). Fo this wok a 0.25 kw thee-phase bushless moto has been seleted. It has an intenal stato solidal with the wheel hub and an extenal oto otating at the wheel speed. The eleti mahine is positioned on the font wheel fo a simple installation. The powe tansmission system is of the diet dive type, so that geas and oupling joints ae avoided. A losed loop ommutation system makes it possible to egulate the mahine voltage and then to ontol the absobed uent. The load toque depends on the oad itineay; aoding to the mehanial assistane level, Fig Powe flows As it is evident fom the sheme, the ylist input is the ondition to obtain assistane fom the eleti moto. A senso will have to detemine the motion dietion if a musula populsion is pesent, egadless of the oad onditions and slope. The ontol system is made up by the following main omponents: thee oto position Hall tansdues with deode logi iuits, a main invete fo the alimentation of the moto and the imposition the speifi uent wavefom fo eah load ondition, a bidietional onvete to allow uent flow between the battey pak and the moto, popotional-integal egulatos to manage RE&PQJ, Vol. 1, No.6, Mah 2008

3 the signal oming fom the ompaison between the efeene uent and the one measued at the moto, a Pulse Width Modulato (PWM) invete fo the geneation of the efeene uent system. Stating fom the equivalent iuit of a bushless d moto and its equation (3), V ( R I( + s L I( + E( (3) as the indued emf depends on the moot otation speed, by means of the Hall tansdue it is possible to obtain the istantaneus speed that leads to an indued emf Ê(. With a good appoximation Ê( an be onsideed equal to the ideal indued emf E(. Adding those quantities in the thid node of the sheme in Fig. 5, the system emains independent fom suh eletial paamete. unwanted aeleations with a onsequent impovement of the battey autonomy. A. Bidietional onvete Suh onvete allows the uent flow in both dietions: fom the battey to the moto when the eletial mahine is woking as a moto, to the battey, when it is woking as a geneato. In the moto mode, as mentioned above, the main ondition to obtain the moto assistane is that the ylist is pedalling in the fowad dietion. The onvete, in the step-down mode, assues a onstant link voltage value fo souing the invete. It has to keep the link voltage independent fom the battey output voltage (V d ) whih is onneted with its state of hage. Fig. 6 shows a sheme fo the step-down onvete. Fig Closed loop egulation of phase uent i a The tansfe funtion F(, epesenting the d moto, shows a pole that stongly influenes the system output. The pesene of a popotional-integal egulato offes a solution to suh a limitation. The expession of the losed loop tansfe funtion W( pesents a pole that depends on the phase total esistane and on the onstant of the integal egulato K i whih allows to manage the system output within a ange of vaiations of the input signal. To optimise the dive opeation, the eletomagneti toque should be independent fom the angula position of the oto. In othe wods, the phase diffeene between the magneti field podued by the pemanent magnets and that podued by the stato uents should be maintained equal to 90. A patiula uent ommutation sequene has to be imposed. The pesene of the thee Hall-effet sensos allows to know the instantaneous oto position and to pefom a oet phase uent ommutation. The egulato output voltage signal is sent to and ompaed with the onstant fequeny tiangula signal, in ode to geneate the stati swith ommand signals of the powe invete. Stating fom a genei oto position θ, being i zeo, and having the uents and the indued emf s the same magnitude, the toque is T e e a a + eb ω b + e 2 e ω This expession keeps its validity fo any θ, if a etangula uent wavefom is hosen in the stato phases. By means of the studied losed loop ontol system, fo eah load ondition the moto supplies the oet toque, depending on the level of assistane equied, avoiding (4) Fig Step-down onvete When the eletial mahine is woking in the geneato mode, the uent flows towad the battey pak fo the egeneative baking. In this ondition it is neessay to use a step-up onvete (Fig. 7) Fig Step-up onvete 5. Regeneative Baking The battey types hosen in this wok ae Nikel Metal Hydate with a nominal voltage of 36V and a 9Ah apaity. Sine the level of assistane is stongly influened by the battey ange, the management of the battey hage and dishage phases is patiulaly impotant. The possibility to eove the baking enegy is of geat inteest in designing the eletial dive. The egeneative powe ontol fo eleti biyle method is a simple and low-ost solution [5]. Unde appopiate onditions, the batteies an be ehaged. Duing a deeleation o baking, an amount RE&PQJ, Vol. 1, No.6, Mah 2008

4 of kineti enegy is usually lost as fition on the wheel. The egeneative baking system allows eoveing pat of suh kineti enegy, to be used to feed eithe the battey o the eletial dive. The intemittent haateisti of the itineay lead by the ide an be smoothed by the intodution of a supeapaito bank. As it is known, a supeapaito an stoe amounts of enegy and then distibute it depending on the equied powe, minimising the enegy losses. The supeapaito bank aises the total weight of the dive of appoximately 3kg, but avoids the eletomagneti stesses on the main soue of the pedele, impoving the battey pefomane and ineasing the autonomy and the life of the battey itself. Unde speifi onditions, imposed by a bidietional onvete, in a patiula time inteval a egeneative bake an be obtained. The oe of the system is epesented by a Buk-Boost onvete with IGBT powe stati swithes. The Boost side is onneted to the supeapaitos bank, the Buk side to the battey pak (see Fig. 8). The ontol system measues the following quantities: the battey and the supeapaitos bank voltages, the state of hage of the battey, the biyle speed, and the instantaneous uents on the load and on the supeapaitos bank. A mioontolle elaboates those quantities and geneates a ommutation sequene by means of the PMW tehnique to ontol the powe stati swith. When the biyle exeeds a etain speed, the mioontolle lets the supeapaitos dishage; if the vehile is stopped, the supeapaitos ae haged, stoing the aumulated enegy. The battey voltage level indiates how the vehile is moving: aeleation leads to its edution, in the opposite ase, it leads to its inease, and the egeneative baking happens. In the latte ase the ontol system ativates the Buk onvete to stoe pat of the kineti enegy in the supeapaitos bank. Duing the aeleation phase T 1 is in swith mode allowing enegy tansfe fom the supeapaitos to the battey. In the egeneative phase (deeleation) T 2 is in swith mode allowing an opposite enegy flow. This last opeation is only possible when the ylist stops pedalling. The bake leve allows two diffeent modes: eletomagneti and mehanial. The above mentioned opeations ae managed by the mioontolle and its funtion is the ombination of two main ontol levels: pimay and seonday. The fist aims at geneating a efeene uent I ef to be feed to the supeapaitos bank, in any load ondition. Its inputs ae: load uent I load, battey voltage V bat, and supeapaitos voltage V ap. This fist ontol maintains the ight enegy level inside the supeapaitos bank by means of the biyle speed V and of the state of hage of the battey. Fig Contol system fo the egeneative baking RE&PQJ, Vol. 1, No.6, Mah 2008

5 I ef is sent to the seond level ontol, whee the uent to ompensate the supeapaitos hage will be alulated. In this level the PWM signal is geneated. As an example, Fig. 9 and Fig. 10 show some esults of the simulations fo the aeleation and deeleation (baking) phases. omponent opeation, detemining in patiula a pope value of the moto toque with espet to the load and of the absobed uent. In this way, undesied aeleations an be avoided and the battey ange an be ineased. Also a suitable egeneative baking system, based on the supeapaito tehnology, has been studied. Suh a system an edue the eletomagneti stesses of the battey pak ineasing the battey life and eduing the maintenane osts (peiodi substitution. Refeenes Fig Aeleation phase In the fist ase it has been onsideed an aeleation fom 4km/h to 8km/h. In the seond ase the ylist stops pedalling. [1]. H. Oman, W. C. Mohin, F. E. Jameson (1995), Eletibiyle populsion powe, Mioeletonis Communiations Tehnology Poduing Quality Poduts Mobile and Potable Powe Emeging Tehnologies, p 555 [2]. W.C. Mohin (1994), Battey-poweed eleti biyles, Nothon/94 Confeene Reod, pp [3]. A. Muetze, Y. C. Tan (2005), Pefomane evaluation of eleti biyles, Industy Appliations Confeene, Volume 4, pp [4]. E. Stashih, A. Muetze (2007), Compaison of the Pefomanes of Diffeent Geaed Bushless-DC Moto Dives fo Eleti Biyles, Eleti Mahines & Dives Confeene IEEE Intenational, Volume 1, pp [5]. N. Somhaiwong, W. Ponglangka (2006), Regeneative Powe Contol fo Eleti Biyle, SICE-ICASE Intenational Joint Confeene, pp Fig Regeneative baking phase With the above tehnial solutions, a pefomane impovement up to 15-20% an be obtained. 6. Conlusions A numbe of diffeent aspets thust the use of eleti biyles in diffeent situations. These inlude lowe enegy ost pe distane tavelled fo a single ide, savings in othe osts suh as insuanes, lienses, egistation, paking, impovement of the taffi flow, envionmental fiendliness, and the health benefit fo the ide. In the pape, the design of an eletial dive fo a motoised biyle is desibed, using ommeial omponents available on the maket. On the basis of tehnial-eonomial onsideation, the feasibility of suh a system fo industial podution has been analysed. A dynamial model has been used to simulate the system behaviou in a numbe of diffeent situations. A losedloop ontol iuit allows the optimisation of the RE&PQJ, Vol. 1, No.6, Mah 2008