Economic Viability Study of an On-Road Wireless Charging System with a Generic Driving Range Estimation Method †
Abstract
:1. Introduction
- Battery swapping [4,6]: the on-board battery is replaced at regular intervals at battery charging stations. The infrastructural costs and required battery capacity are high. While the transport efficiency is more due to a small on-board battery, the increase in required driving range leads to the increase in the number of battery swapping operations.
- Hybrid vehicles [6]: a combination of two or more energy sources are used. The design is complicated, and the vehicle cost is high. Transport efficiency decreases with the increase in on-board energy buffer weight.
2. Generic Methodology for Driving Range Estimation
Parameter | Value | Unit |
---|---|---|
Empty mass | 13,300 | kg |
Gross mass | 19,000 | kg |
Frontal area | 8.568 | m |
Coefficient of drag (assumed) | 0.7 | - |
Coefficient of rolling resistance (assumed) | 0.01 | - |
Battery capacity | 600 (200 × 3) | Ah |
Energy capacity | 324 | kWh |
Nominal voltage | 540 | V |
Battery type | lithium ion | - |
Initial state of charge (SoC) (assumed) | 95% | - |
Allowed depth of discharge (assumed) | 80% | - |
- Aerodynamic drag () is the load due to resistance offered by the air. ρ is the density of air in kg/m; is the coefficient of drag; vis the instantaneous velocity; and is the frontal area of the vehicle.
- Rolling resistance () is the frictional resistance offered by the road due to the motion of wheels. is the coefficient of rolling resistance; M is the mass of the vehicle; g is the acceleration due to gravity; and θ is the angle of inclination.
- Inertial load () is the change in the stored energy of the vehicle due to dynamic motion (acceleration/braking). It is important to consider here that some energy is recoverable through the regenerative braking.
- Gravitational load () is due to the movement of the vehicle on an inclined road.
- The overall average efficiency of the motor-drive system is assumed to be 80%. A corrective factor corresponding to the ratio of assumed average efficiency to actual average efficiency can be multiplied with the mass and area constant derived in the subsequent section to improve the accuracy of the model.
- Sixty percent of energy is recovered during regenerative braking.
- The angle of inclination of the road is zero.
- The auxiliary power P will include heating, ventilation and air conditioning (HVAC), lighting, auxiliary services of vehicle, opening and closing of doors, route display screens, power steering and brakes. In the simulations to derive K and K, 0 kW is considered in order to eliminate the dependence of SoC on P.
- Actual measurements were taken for the 12 m bus with a 324 kWh battery for SORT 1, 2 and 3 cycles. The specific consumption was measured to be 1.2 kWh/km for SORT 3 as compared to 1.3 kWh/km obtained from the simulation of our dynamic power consumption model under similar conditions. This increased the confidence on relying on the developed model for the economic viability study.
2.1. State of Charge Estimation of the Battery-Alone System
2.1.1. Mass Constant () of the Driving Cycle
2.1.2. Area Constant () of the Driving Cycle
2.1.3. Equation for State of Charge Estimation of the Battery-Only System
Driving cycle | () | () | (km/h) |
---|---|---|---|
SORT 1 | 2.09234 ×10 | 2.4684 × 10 | 12.1 |
SORT 2 | 1.9604 ×10 | 4.9201 × 10 | 18 |
Braunschweig | 2.1225 ×10 | 4.992 × 10 | 22.9 |
SORT 3 | 1.9464 ×10 | 8.9739 × 10 | 25.3 |
UDDS | 1.89 ×10 | 9.3371 × 10 | 31.53 |
HWFET | 1.3371 ×10 | 2.2176 × 10 | 77.73 |
2.2. Driving Range Extension with the Static Inductive Power Transfer System
2.3. Driving Range Extension with the Dynamic Inductive Power Transfer System
- The final SoC linearly increases with road coverage area despite the randomness in the velocity profile. This is because the IPT system is also randomly distributed on the road track. Regression analysis yields , which indicates a strong correlation.
- The slope is directly proportional to the charging power level of the IPT system.
2.4. Impact of Battery Weight
2.5. Estimation Error
3. Economic Analysis for the On-Road Inductive Power Transfer Charging System: Case Study
3.1. System Description
- The battery is charged to its full capacity during night hours when the bus is stationary.
- There are 24 scheduled stoppages of 20 s each and a 6 min stoppage at the start of each run.
- The required driving range is 400 km (10 trips of 40 km each) in the worst case scenario of −15 C, 100% occupancy.
- The climate model in [21] predicts that a normal bus would consume 167 kWh for HVAC in winter days for −7 C in Netherlands for a 20 h operation. An articulated bus of almost double the length would consume double this (334 kWh). Correspondingly, 433 kWh will be consumed if the ambient temperature is −15 C.The total energy consumption of the auxiliary system, including HVAC, lighting, auxiliary services of the vehicle, opening and closing of doors, route display screens, power steering and brakes, during the worst winter condition is assumed to be 500 kWh for a 20 h operation. Therefore, the average is assumed to be 25 kW.
3.2. ΔSoC Deficit Removal with the Static Inductive Power Transfer Charging System
3.3. ΔSoC Deficit Removal with the Dynamic Inductive Power Transfer Charging System
3.4. Cost of System Components
- The cost of the power electronics [26] involved in the IPT supply system is considered to be 50 €/kW. Additional maintenance charges of 10% have been included.
- Corresponding to the operating frequency of 100 kHz, a minimum of 4 inverters per km are installed [27].
- The road construction (digging, labor, installation of IPT system) costs of 0.1 M€/km for IPT road coverage are assumed.
- Discrete charging pads of 1.05 m [24] in length each have been considered for dynamic on-road charging. The total number of dynamic charging pads have been estimated for total road coverage, and the corresponding cost of air cored primary winding is calculated. An illustration of the on-road dynamic charging system with discrete pads [28] is shown in Figure 11.
4. Second Order Economic Considerations
4.1. Running Schedule
4.2. On-Board Battery Capacity
- The transport efficiency increases with decreasing battery capacity corresponding to the weight reduction. The energy savings becomes significant with a high lifetime travel distance and the number of running buses.
- IPT charging infrastructure cost increases with decreasing battery capacity due to the additional road coverage requirement of the dynamic IPT system. This is shown in Figure 13.
- The price of the installed on-board battery decreases with decreasing capacity. This can be a significant investment factor with increasing the number of e-buses.
5. Conclusions
Parameter | Value | Unit |
---|---|---|
On-board battery capacity | 500 | kWh |
Driving range in worst loading scenario | 400 | km |
Driving range without on-road charging | 119 | km |
Scheduled stoppage at start of each run (worst case) | 12 | min |
Scheduled stoppage at start of each run (normal) | 6 | min |
Number of buses (average running + spare) | 25 + 5 | - |
Static charging power level | 200 | kW |
Dynamic charging power level | 200 | kW |
Dynamic IPT road coverage | 13% | - |
Power rating of inverter | 200 | kW |
Total number of inverters | 22 | - |
Cost of primary winding | 5.67 | M€/lane |
Cost of inverters | 0.24 | M€/lane |
Total cost of IPT system | 6.45 | M€/lane |
Specific cost | 1.2 | M€/km/lane |
Battery cost for 30 buses | 10.5 | M€ |
Total project cost (M€/2 lanes/30 buses) | 23.4 | - |
Acknowledgments
Author Contributions
Conflicts of Interest
Nomenclature
SoC of battery at the end of the traveled distance | |
Initial SoC of the battery | |
S | Total distance traveled by the vehicle in km |
Mass constant of the driving cycle in | |
M | Gross mass of the vehicle in kg |
Area constant of the driving cycle in | |
Frontal area of the vehicle in m | |
Coefficient of drag | |
Power demand of the auxiliary system of the vehicle in kW | |
Average velocity in km/h | |
Discharge efficiency of the battery | |
Energy capacity of vehicle battery in kWh | |
Capacity factor defined as the ratio of the maximum energy that can be delivered by the EV battery to the maximum energy that can be delivered by the reference battery | |
SoC of battery at the end of traveled distance with a static charging system | |
Total scheduled stoppage time spent on the IPT charging system in hours | |
Charging efficiency of the battery | |
Static IPT charging power level in kW | |
SoC at the end of the total traveled distance without any on-road charging | |
State of the charge of the battery at the end of traveled distance | |
Total travel time in hours | |
Dynamic charging power level in kW | |
% Road coverage of dynamic IPT | |
DR | Driving range in km |
Maximum allowed depth of discharge, assumed to be 80%. |
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Shekhar, A.; Prasanth, V.; Bauer, P.; Bolech, M. Economic Viability Study of an On-Road Wireless Charging System with a Generic Driving Range Estimation Method. Energies 2016, 9, 76. https://doi.org/10.3390/en9020076
Shekhar A, Prasanth V, Bauer P, Bolech M. Economic Viability Study of an On-Road Wireless Charging System with a Generic Driving Range Estimation Method. Energies. 2016; 9(2):76. https://doi.org/10.3390/en9020076
Chicago/Turabian StyleShekhar, Aditya, Venugopal Prasanth, Pavol Bauer, and Mark Bolech. 2016. "Economic Viability Study of an On-Road Wireless Charging System with a Generic Driving Range Estimation Method" Energies 9, no. 2: 76. https://doi.org/10.3390/en9020076
APA StyleShekhar, A., Prasanth, V., Bauer, P., & Bolech, M. (2016). Economic Viability Study of an On-Road Wireless Charging System with a Generic Driving Range Estimation Method. Energies, 9(2), 76. https://doi.org/10.3390/en9020076