Opportunity charging of electric vehicles (EVs) during brief stops is an important application of wireless power transfer (WPT). Irrespective of the specific WPT technology used, it is possible to quantify the effect of opportunity charging on EVs using energy calculations. This paper presents an analysis of the potential reduction in battery size and extension in EV range enabled by opportunity charging, using urban driving cycle data and various charging power levels. Traction power expended for acceleration, and to overcome air drag and rolling friction are considered. Depending on the extent of opportunity charging, battery size reduction from 6% to 85% is possible. Alternatively, retaining the battery size at its base value, a range extension between 7% and 600% is realizable. Although the results are shown for a particular velocity profile, the generalized analysis method presented in this paper can cater to various types of driving cycles. Full paper available here: https://ieeexplore.ieee.org/document/8450900

1. Wireless Opportunity Charging as an Enabling
Technology for EV Battery Size Reduction and Range
Extension: Analysis of an Urban Drive Cycle Scenario
2018 WoW, 3-7 June 2018, Montréal, Canada
Lalit Patnaik, Phuoc Sang Huynh, Deepa Vincent, and Sheldon S. Williamson
University of Ontario Institute of Technology, Oshawa, Canada
ABSTRACT
Opportunity charging of electric vehicles (EVs) during brief stops
is an important application of wireless power transfer (WPT).
Irrespective of the specific WPT technology used, it is possible to
quantify the effect of opportunity charging on EVs using energy
calculations. This paper presents an analysis of the potential
reduction in battery size and extension in EV range enabled by
opportunity charging, using urban driving cycle data and various
charging power levels. Traction power expended for acceleration,
and to overcome air drag and rolling friction are considered.
Depending on the extent of opportunity charging, battery size
reduction from 6% to 85% is possible. Alternatively, retaining the
battery size at its base value, a range extension between 7% and
600% is realizable. Although the results are shown for a
particular velocity profile, the generalized analysis method
presented in this paper can cater to various types of driving
cycles.
Keywords—opportunity charging, wireless charging, wireless
power, battery size reduction, EV range extension, electric
vehicles
INTRODUCTION
A notable application of wireless power transfer (WPT) is
opportunity charging of electric vehicles (EVs) whenever they
stop for a brief while, e.g. at traffic intersections. The two major
categories of WPT are inductive power transfer (IPT) and
capacitive power transfer (CPT). Magnetic induction based IPT
tends to have poor efficiency when the coils are misaligned. CPT
technologies tend to require high switching frequencies (>1 MHz)
that can limit the practically realizable power levels [1]–[3]. For
EV charging applications, magnetic resonance based IPT is
currently the preferred technology. The four power classes
defined by the SAE J2954 standard, for wireless power transfer in
light duty EVs, are given in Table 1 [4]. Irrespective of the specific
WPT technology used, it is possible to quantify the effect of
opportunity charging on EVs using detailed energy calculations.
This paper presents an analysis of potential reduction in battery
size and extension in EV range enabled by opportunity charging,
using urban driving cycle data and various charging power levels.
ANALYSIS APPROACH
Equations (1)-(11) summarize the detailed analysis approach for
calculating battery size and EV range for different levels of
opportunity charging. In order to determine the required battery
size, vehicle data as well as urban driving cycle data are used.
Table 2 lists the vehicle data used in this analysis, with chosen
parameter values. While the specific values could change, the
overall analysis approach would still hold. The driving cycle data
used in this study is the vehicle speed profile v(t) as per the
Urban Dynamometer Driving Schedule (UDDS). In this driving
cycle, the vehicle covers 12 km in 23 minutes with 17 stops.
However, the analysis approach is equally valid for other driving
cycles, with vastly different velocity profiles.
IEEE PELS Workshop on Emerging Technologies: Wireless Power, 3-7 June 2018, Montréal, Canada 1
Equations:
Traction force for acceleration, Faccel = m dv/dt (1)
Traction for overcoming drag, Fair = (1/2) Cdr A ρ v(t)2 (2)
Traction for overcoming rolling friction, Froll = Crr m g sgn(v(t) (3)
Total traction force, Ftotal(t) = Faccel(t) + Fair(t) + Froll(t) (4)
Traction power, P(t) = F(t) v(t) / η (5)
Total energy required for trip, Etotal = ʃ Ptotal(t) dt (6)
Base battery size, B0 = K Etotal (7)
Base EV range, R0 = K s (8)
Energy put in by opportunity charging, Eopp = Pch Σts (9)
EV battery size, B = K (Etotal – Eopp) (10)
EV range, R = B0 s / (Etotal – Eopp) = K s / (1– α) (11)
Power Class Maximum Power Minimum Efficiency
WPT1 3.7 kW 80%
WPT2 7.7 kW 80%
WPT3 11 kw 80%
WPT4 22 kW TBD
Table 1. Power classes as per SAE J2954 standard for
wireless power transfer in light-duty EVs [4].
OBJECTIVES
• Quantify the impact of wireless opportunity charging in
terms of EV battery size reduction and range extension.
• Develop generalized analysis approach using urban driving
cycle data and various charging power levels
• Demonstrate a case study of the analysis approach using
Urban Dynamometer Driving Schedule (UDDS) data.
Parameter Value
Coefficient of rolling friction, Crr 0.01
Mass of vehicle and payload, m 1100 kg
Drivetrain efficiency, η 0.8
Aerodynamic drag coefficient, Cdr 0.5
Frontal area, A 2.5 m2
Battery pack voltage, Vbatt 300 V
Battery sizing safety factor, K 15
Table 2. Sample electric vehicle data.

2. CONCLUSIONS
• Depending on the extent of opportunity charging, battery size
reduction from 6% to 85% is possible.
• Retaining the battery size at its base value, a range extension
between 7% and 600% is realizable.
• Proposed analysis method can aid application engineers as
well as policy makers in identifying charging opportunities
and deciding on their infrastructure installation requirements.
RESULTS
Opportunity No. Start Time (s) Stop Duration (s)
1 0 21
2 125 39
3 429 19
4 552 17
5 620 26
6 1023 30
7 1153 16
8 1313 25
Table 3. Charging opportunities with stop time > 15 s for
UDDS driving cycle. Refer Fig. 1(a).
REFERENCES
[1] M. P. Theodoridis, “Effective capacitive power transfer,” IEEE Transactions on
Power Electronics, vol. 27, no. 12, pp. 4906–4913, 2012.
[2] F. Lu, H. Zhang, H. Hofmann, and C. Mi, “A double-sided LCLC-compensated
capacitive power transfer system for electric vehicle charging,” IEEE Transactions on
Power Electronics, vol. 30, no. 11, pp. 6011–6014, 2015.
[3] F. Lu, H. Zhang, and C. Mi, “A review on the recent development of capacitive
wireless power transfer technology,” MDPI Energies, vol. 10, no. 11, pp. 1752, 2017.
[4] SAE Standard J2954, “Wireless Power Transfer for Light-Duty Plug-In/Electric
Vehicles and Alignment Methodology,” Nov. 2017.
Fig 1. Time variation of various quantities during UDDS driving cycle. (a) Vehicle
speed. Charging opportunities with stop time greater than 15s are shown. (b)
Distance covered. (c) Vehicle acceleration. (d) Traction force. (e) Traction power.
From the power profile, Etotal =1.504 kWh.
Fig. 2. Effect of opportunity charging on battery size and EV range. (a,b,c) Battery
sizes, size reduction, and resulting charging C-rate for a given EV range, R0 = 180 km.
(d,e,f) EV range, range extension, and charging C-rate for a given battery size,
B0 = 22.56 kWh. n = number of charging opportunities in a 12 km ride (UDDS).
Wireless Opportunity Charging as an Enabling
Technology for EV Battery Size Reduction and Range
Extension: Analysis of an Urban Drive Cycle Scenario
2018 WoW, 3-7 June 2018, Montréal, Canada
Lalit Patnaik, Phuoc Sang Huynh, Deepa Vincent, and Sheldon S. Williamson
University of Ontario Institute of Technology, Oshawa, Canada