Parameters Optimization of PHEV Based on Cost-Effectiveness from Life Cycle View in China Jiuyu Du, Hewu Wang and Minggao Ouyang Abstract Plug-in hybrid electric vehicle (PHEV) technology combining the merits of Battery electric vehicle (BEV) and Hybrid electric vehicle (HEV), has the potential to reduce greenhouse gas (GHG) emissions, and petroleum consumption in the transportation sector. However, the cost-benefit of PHEVs mainly determined by battery technology, optimal powertrain design, and vehicle kilometers daily traveled and charging habits. Targeting to cost-benefit, the optimal design method was presented, taking battery cycle life Vs DOD data, driving data, battery performance data into consideration. The method provided optimal vehicle designs to realize minimum life cycle cost, and maximum petroleum consumption under different scenarios. For A-segment equivalent PHEV (similar to a F3DM), under Shanghai urban driving conditions, it can be find that while PHEVs with present traction battery technology, 30 km AER was most life cycle cost-effective to obtain maximum petroleum displacement based on Shanghai driving data. Large capacity battery lead to petroleum displacement not so much as cost increased. At China electricity price off peak, Li-ion battery pack costs must fall below ø2.0/wh to be cost competitive with equivalent internal combustion engine vehicles (ICEs). Keywords Plug-in hybrid Cost-benefit Parameters optimization All electric range Vehicle kilometers daily traveled F2012-B03-037 J. Du (&) H. Wang M. Ouyang (&) State Key Laboratory of Automotive Safety and Energy, Tsinghua University, Beijing 100084, China e-mail: dujiuyu@tsinghua.edu.cn M. Ouyang e-mail: cerc-cvc@tsinghua.edu.cn J. Du H. Wang M. Ouyang China Automotive Energy Research Center (CAERC), Beijing, China SAE-China and FISITA (eds.), Proceedings of the FISITA 2012 World Automotive Congress, Lecture Notes in Electrical Engineering 191, DOI: 10.1007/978-3-642-33777-2_58, Ó Springer-Verlag Berlin Heidelberg 2013 697
698 J. Du et al. 1 Introduction With rapid development of economy and urbanization, production and stock of vehicle increased sharply. By the end of 2011, the automotive production has been increased to 18.505 M [1], which aggravated the issues of energy security and environmental pollution of urban area became more seriously. Accordingly, the crude oil dependence of China has reached to 56.5 % [2]. The GHG emission mainly comes from vehicles tailpipe in urban area [3]. Electric powertrain has been considered as solution to energy consumption and emission of GHG in urban area. Electric vehicles (including hybrid electric vehicle, plug-in hybrid electric vehicle, battery electric vehicle, fuel-cell electric vehicle) can effectively reduce fuel consumption and exhaust emission, and developing electric powertrain technologies has been chose as national sustainable transportation strategy. Pure electric vehicle can realize 100 % alternative to crude oil. However, subjecting to the key technologies limitation, electric powertrain vehicles is less competitive to conventional vehicles. A PHEV has been defined by SAE [4] as: A hybrid vehicle with the ability to store and use off-board electrical energy in the RESS. These systems are, in effect, an incremental improvement over the HEV, with the addition of a large battery with greater energy storage capability, a charger, and modified controls. So PHEV technology integrated the advantages of BEV and HEV, will be the best choice of transit powertrain technology to all electric driving stage, and it is considered a potential near-term approach to addressing global warming and dependency on foreign oil in the transportation sector of China, as the cost, size, and weight of batteries are reduced. To design a PHEV powertrain, more battery capacity will lead to more displacement of fuel, in other words, increased AER will result in a larger portion of travel propelled by electrical energy instead of gasoline, however, higher cost and lower system energy efficiency. Distance the vehicle is driven between charges plays an important role in determining the PHEVs advantage: Vehicles that are charged frequently can drive most of their miles on electric power, even with a relatively small battery pack, while vehicles that are charged infrequently require larger battery packs to cover longer distances with electric power. Meanwhile, at present, the PHEV testing standards is version translated from that of EU. Because the driving cycle and personal daily kilometer traveled in China is totally different from EU s, so how to design powertrain parameters optimized based on the AER, maximum speed, driving cycle is challenging problem. The potential for PHEVs to displace fleet petroleum consumption derives from several factors [5, 6], including duty cycle, daily kilometer distribution, electric powertrain technology and components optimal sizing, etc.
Parameters Optimization of PHEV Based on Cost-Effectiveness 699 Fig. 1 City duty cycle of passenger car in China vehicle speed/km.h -1 80 60 40 20 0 0 200 400 600 800 1000 1200 time/s 400 distribution density 300 200 100 0 0 10 20 30 40 50 60 70 80 vehicle speed/km.h -1 2 Duty Cycle of Passenger Car in China To design electric vehicle more cost-benefit, parameter associated with dynamic performance of electric car should be designed economical based on the operating condition such as duty cycle of electric car in urban area of China. From Fig. 1, it can be seen that the maximum speed is no more than 80 km/h. 3 Driver Behavior To accurately calculate fuel costs for selected vehicles it is important to know how a user drives and how much of the vehicle s total mileage is driven using each fuel type. This is especially important for plug-in hybrid vehicles, which operate using both gasoline and electricity from the grid. In this study, we used data of vehicle kilometers daily traveled in Shanghai to investigate the optimization method of PHEV targeting cost-benefit. The characteristics of daily kilometers driven distribution in Shanghai was shown in Fig. 2. 4 Components Sizing Based on the driving cycle shown in Fig. 1, the parameters of traction motor could be determined, thereby the power of traction battery was known. The parameters of prototype electric sedan chose to analyze were shown in Table 1.
700 J. Du et al. Fig. 2 VKDT of Shanghai Tablel 1 Electric sedan parameters assumptions Items Values Glider mass, kg 900 Curb mass, kg 1,350 Gross vehicle mass, kg 1,800 C D 0.35 A 2 f 0.012 Acceleration time, s 0 50 km/h 9(CD) 50 100 km/h 12(CS) Gradeability, % 20 5 Electric Motor Based on the vehicle dynamic theory, the motor power is P m ¼ 1 1 1 1 g T g B g G 3600 mgfu du a a þ mgiu a þ mdu a þ C DAu 3 a ð1þ dt 76140 Where g T is efficiency of transmission system, g B is charging efficiency of traction battery, g G is efficiency of electric motor; A is frontal area, m 2 ; m is curb weight of electric car, kg; u a is speed of vehicle,km.h -1 ; g is gravity acceleration,m.s -2 ; C D is drag coefficient; f is rolling resistance coefficient; i is gradeability; d is rotary inertia conversion factors. 6 Traction Battery The capacity of traction battery is:
Parameters Optimization of PHEV Based on Cost-Effectiveness 701 E b ¼ 1 m glider gs AER 3600gu a Electricity consumption is: fu a þ iu a þ d u a du a g dt þ S AER C D Au 3 a gu a 76140 ð2þ gs AER ð Þgu a fu a þ iu a þ d u a du a g dt 3600DE 1 SOC Min E ele ¼ 1 Z T Z T P m dt g g ep g B g G g T P reg dt m 0 0 Where P reg is regenerative power, kw; g ep is efficiency of power electronics. ð3þ 7 Ownership Cost Analysis For the calculations lifecycle ownership cost of PHEV, each driving type is further broken down into kilometers on electricity and kilometers on gasoline. The user may select one of three recharging schedules for normal daily use driving twice per day, once per day, or every other day. When fully charged, the PHEV is capable of operating on grid-derived electricity for a limited number of kilometers. The potential average daily kilometers driven on electricity is set at AER times the number of recharges per day (RPD). If the normal daily driving mileage is greater than the potential daily miles on electricity (as defined by RPD times AER), the PHEV uses electrical power until the batteries are depleted, and gasoline is used for the remainder of the daily miles. The city-highway mileage split is assumed to be the same for the miles on electricity and the miles on gasoline. If the value of RPD times AER exceeds the normal daily mileage, only electric power is required for normal daily driving. The ownership cost composed of energy consumption, battery displacement, maintenance, tires, insurance, license, and registration. Because the cost of maintenance, tires, insurance are relatively fixed and low [7] (as Fig. 3), so this study, they are not taken into consideration. The lifecycle ownership cost was C oc ¼ C ele þ C gas þ C bat chg ð1þ Because of the limitation of traction battery cycle life, during the PHEV operation life, the battery replacement is required. The cost of that was C bat chg ¼ d bate b S VKDT L cyc ðdod%þs AER ð2þ The calculation of electricity consumption in CD mode was divide into two scenarios. If S AER C S VKDT, the cost functions are
702 J. Du et al. Fig. 3 Cost structure of some typical PHEV Fig. 4 TCO of PHEV under gasoline price scenario C ele ¼ nns KDT E E P elec ðc gas ¼ 0Þ ð3þ C bat chg ¼ d bate b S VKDT L cyc ðdod%þs AER ð4þ If S AER \ S VKDT, the cost functions are C ele ¼ nns AER E E P ele ð5þ C gas ¼ nnðs VKDT S AER ÞFE gas P gas ð6þ C bat chg ¼ d spb E b L cyc ð100%dodþ ð7þ
Parameters Optimization of PHEV Based on Cost-Effectiveness 703 Fig. 5 TCO of PHEV under battery specific price scenario Fig. 6 TCO of PHEV under electricity price scenario Where C oc is the ownership cost of the EV in operating life, C ele is the cost of electricity consumption, C bat chg is the cost of traction battery replacement, Yuan/ pack; S AER is all electric range of EV, km; d bat is the specific price of traction battery, Yuan/Wh; n is operating days in a year, n = 360; N is the operating life in years of PHEV, N = 15 years; C cpis capital price of PHEV, yuan; d spb is specific price of traction battery, yuan/kwh; E E is electricity consumption ratio, kwh/ 100 km; P ele is price of electricity, Yuan/kWh; r is general discount rate; L cyc ðdod%þ is function of cycle life associated with DOD (Depth of Discharging); FE gas is fuel economy of CS mode of PHEV, L/100 km; P gas is price of gasoline, yuan/l; S VKDT is vehicle traveled distance daily in kilometers, km.
704 J. Du et al. 8 Conclusions Based on the VKDT of Shanghai city and passenger car city cycle, the TCOs of PHEV subjected to different parameter of AER under different scenarios were performed (Figs. 4, 5, 6). From above analysis, it could be concluded: 1) Gasoline price affects TCO greatly, and lower price corresponds to lower optimal value of AER. 2) When gasoline price was 8 yuan/l, the optimal AER would be 25 km targeting to cost-benefit, and when gasoline price increased to 16 yuan/l, accordingly the optimal AER would be 30 km. Traction battery specific and cycle life is the most important affective factors to TCO of PHEV. When the specific cost of battery was decreased to 1.5 yuan/wh, the trend almost was that more AER leads to better cost-benefit. At present level, the AER 28 was recommended. 3) The electricity price has minimum impact on TCO of PHEV From the price of commercial use electricity to off-peak electricity price, the optimal AER were 25 30 km. Acknowledgments Thanks to the subsidy of International S&T Cooperation Program of China (ISTCP):2010DFA72760 References 1. CAAM. The automotive industry production and sales by the end of 2011 [EB/OL], 2012-01- 10/2012-07-18. http://www.caam.org.cn/zhengche/20120112/1605066964.htm 2. Sina. Import of crude oil increased by 6% and oil dependence increased to 56.5% in 2011[EB/ OL], 2012-01-13/ 2012-07-20. http://finance.sina.com.cn/chanjing/cyxw/20120113/02301119 1685.shtml 3. MEP. China Vehicle Pollution Prevention Annual Report (2010) (English abstract in Chinese) [R], Beijing: MET, 2010. 4. SAE J1715. Hybrid Electric Vehicle (HEV) & Electric Vehicle (EV) Terminology [S]. U.S.SAE 2008 5. Simpson A (2006) Cost-benefit analysis of plug-in hybrid electric vehicle technology [z]. Yokohama, Japan 6. Kloess M (2009) The role of plug-in-hybrids as bridging technology towards pure electric cars: an economic assessment [z]. Shenzhe, China 7. DAE of THU. Survey of industry of electric vehicle in China [R]. Beijing. 2010.