Performance Evaluation of Square Coupled Coils at Different

Misalignments for Electric Vehicle Battery Charging

P. Srinivasa Rao Nayak, Kishan Dharavath, Radhakrushna Dey,

K. Sundareswaran and Sishaj P. Simon

Electrical and Electronics Engineering, National Institute of Technology - Trichy, 620015, Trichy, Tamil Nadu, India

Keywords: Wireless Power Transfer, Mutual Inductance, Electric Vehicle, Misalignment.

Abstract: Wireless Power Transfer (WPT) for electric vehicle battery charging is an advancing battery charging

technology. The crucial part in the WPT system is the coupling coil structure and it plays a major role in

effective power transfer. This paper describes the mutual inductance and flux distribution characteristics of

the square coupled coils with different misalignments also to make more realistic for Electric Vehicle (EV)

battery charging applications the coupled coils are designed with and without core and chassis. The

evaluation contains the mutual inductance gets affected by distance between the coils, lateral and angular

misalignment effects. The results of the analysis are used in the implementation of the wireless EV battery

charging system.

1 INTRODUCTION

The popularity of Electric propulsion vehicle in

automobile industry sector has always been

increasing due to many positive aspects of energy

efficiency, environment friendliness, performance,

and reduced energy dependence on fossil fuels.

However, the use of EV faces some challenges like

driving range, recharge time, battery cost, more

bulk, and weight (Khaligh, 2012), (S. Li, 2014).

Thus, with the growing EV market, we need to

overcome the problems by stimulating new ideas

and developments in this area. On that concern EV

battery charging is an emerging research area. In

conventional conductive battery charging introduces

the inconvenience and risk hazards and this type of

problems can be overcome by a simple concept

wireless battery charging (Roman, 2016), (Seho

Kim, 2017). The principle of the wireless power

transfer (WPT) is like conventional transformer i.e.,

mutual induction. When a current carrying

conductor or coil is excited with alternating source it

will produce magnetic field around the conductor or

coil. When another coil is brought in the vicinity of

the magnetic field of the first coil an EMF will be

induced due to alternating nature of the magnetic

field (F. Y. Lin, 2015), (Fariborz, 2014). In the WPT

system coil connected to the source is referred as

transmitter coil (Tx), and the coil connected to the

load called as receiver coil (Rx).

However, the potency of the power transfer over

this inductive link predominantly depends on flux

linkages between the coupled coils and structure of

the coils. Based on the specific application, the coil

structures like circular, rectangular, DD & DQ and

square shapes (C. Y. Huang, 2015), (Ezhil, 2015)

can be used. The shape of the coil and misalignment

greatly affects the mutual inductance and flux

linkage between the coupled coils. The amount of

power transfer and efficiency mainly depends on MI

(Dharavath, 2016). So, it is necessary to obtain the

MI for designing of the any wireless power transfer

system in particularly EV battery charging

application. The design and optimization of circular

magnetic structure is described (M. Budhia, 2011)

for wireless EV battery charging applications. Based

on the 3D field the mutual inductance between the

circular coupled coils is obtained for IPT system

(Yang Han, 2015) and presented the misalignment

conditions for circular coupled coils. (Merugu,

2016) explained the effect of spiral square coil

dimensions of the square coupled coils on power

transfer capability, efficiency.

In this paper coupling characteristics of square

inductive coupled coils are described with different

misalignments. The basic schematic diagram

representation of wireless electric vehicle battery

290

Nayak, P., Dharavath, K., Dey, R., Sundareswaran, K. and Simon, S.

Performance Evaluation of Square Coupled Coils at Different Misalignments for Electric Vehicle Battery Charging.

DOI: 10.5220/0006672402900297

In Proceedings of the 4th International Conference on Vehicle Technology and Intelligent Transport Systems (VEHITS 2018), pages 290-297

ISBN: 978-989-758-293-6

charging system is shown in Figure.1. The figure

gives the power flow in the WPT system.

The WPT system representation of schematic

diagram consists of High-frequency inverter,

transmitter, and receiver compensation circuits,

inductive coils and battery charging unit. The high-

frequency inverter converts the DC input supply to

high-frequency AC supply. The output of the

inverter is fed to power compensation circuits which

are used for performance improvement of the

wireless power transfer system. The transmitter and

receiver coil are connected to respective

compensation circuits. The power transfer takes

place between inductive coils maintained at the

proper air gap. Battery Charging unit includes

suitable power converters and the battery pack to be

charged and it is connected to the receiver side of

the system.

Figure 1: Basic schematic diagram of the WPT system.

This paper is organized into five sections.

Section 2 describes possible misalignment variation

of the square coils. Correspondingly finite element

modeling (Ansys Maxwell simulation) is presented

in section 3. Results and discussions are described in

section 4 and the conclusion is given in section 5.

2 POSSIBLE MISALIGNMENTS

IN SQUARE COUPLED COILS

This section presents the possible variations of

misalignments of the transmitter and receiver coils

such as perfect alignment, lateral or planar

misalignment and angular Misalignments. The

misalignments of the coupled coils are shown in

Figure. 2. Figure. 2(a) depicts the perfect alignment

of the transmitter and receiver coils i.e. the

coinciding axes of the flat planar surface. For

instance, when receiver coil is moved some more

distance away in vertical from transmitter coil the

flux linkages will decrease which as a result in a

decrement of mutual inductance. In the above case,

the coupling between them is weak. If transmitter

and receiver coils are perfectly aligned, and vertical

distance between them is very less, the flux linking

with the receiver coil is more, and the coupling

between them is strong. Also, the mutual inductance

is very high. Figure. 2(b) shows lateral misalignment

between the transmitter and receiver coil. In this

case transmitter and receiver, coils are placed in a

parallel plane and varied in horizontally. In

contradiction to the above two alignments, in

angular misalignment and Lateral and Angular

Misalignment (as shown in Figure.2 (c) to 2 (d)) the

mutual inductance between the coils depends on

horizontal, vertical distance and tilted angle since

they are placed at certain angle (0

to 30

) up or

down. In all the above misalignments the inductive

coupling characteristics are investigated.

(a)

(b)

(c)

(d)

Figure 2: Various misalignment of square inductive coils

(a) Perfect Alignment (b) Planar Misalignment, (c) Angu-

lar misalignment, (d) Planner and angular misalignment.

Performance Evaluation of Square Coupled Coils at Different Misalignments for Electric Vehicle Battery Charging

291

3 MODELING AND

DEVELOPMENT OF SQUARE

COUPLED COIL STRUCTURE

IN FEM (ANSYS MAXWELL)

Finite Element Modelling tool-ANSYS MAXWELL

is one of the world’s leading engineering simulation

tool for real-time simulations with design and

analysis of electromagnetic and electromechanical

devices, including motors, actuators, transformers,

sensors and coils. In this section, ANSYS

MAXWELL is employed to estimate the mutual

inductance and flux distribution of the square

coupled coil with different misalignments which

were discussed in section 2. In this software, all

simulations are carried out using 2-D FEM

modelling. Maxwell’s field distribution calculator

calculates the magnetic flux linked with the receiver

coil. The transmitter and receiver coils are

developed by the simulation tool with different

misalignment is as shown in Figure. 3. The FEM

coil setup with ferrite core for suitable applications

for EV battery charging are shown in Figure. 4.

In this modelling 0.25cm diameter solid copper

wires are used. Coil winding has started at a distance

of 4cm from their origin. Both the coils are made up

of equal number of turns as 12 and the gap between

each turn is 0.018cm, 16 x 16 x 0.1cm dimensioned

ferrite core and 24 x 24 x 0.2 dimensioned steel

chassis are used for transmitter and receiver coils.

The gap between core and coil is set to 0. 07cm.The

transmitter coil is energized by 5A AC current.

(a)

(b)

(c)

(d)

Figure 3: Square Coil arrangement in FEM Simulation (a)

Perfect Alignment (b) Planner Misalignment, (c) Angular

misalignment, (d) Planner and angular misalignment.

(a)

(b)

Figure 4: Square Coil arrangement in FEM Simulation (a)

Coil setup with Ferrite Core (perfect alignment), (b) Coil

setup with Ferrite Core (misalignment).

4 RESULTS AND DISCUSSIONS

The flux lines between the square inductive coupled

coils at 5cm vertical distance with different

misalignments for both air cored, ferrite cored and

ferrite core with chassis structure are shown in

Figure. (5), Figure. (6) and Figure. (7) respectively.

As if the receiver coil moves away from the

transmitter coil the flux linkage will reduce as a

result in reduction of mutual inductance.

The mutual inductances are computed between

the coupled coils with all misalignment conditions

which are the vertical distances 8cm, 12cm, 16cm,

20cm and 24cm for each horizontal distance such as

0cm, 5cm and 10cm and also for each angular

variation such as 0°, 15° and 30° for both at air

cored, ferrite cored and ferrite core with chassis

structure and it is shown in Figure.7. section must be

in one column.

(a)

Figure 5: 2-D Magnetic flux distribution between coupled

coils Without core (a) Perfect Alignment, (b) Planar

Misalignment, (c) Angular misalignment, (d) Planar and

angular misalignment.

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292

(b)

(c)

(d)

Figure 5: 2-D Magnetic flux distribution between coupled

coils Without core (a) Perfect Alignment, (b) Planar

Misalignment, (c) Angular misalignment, (d) Planar and

angular misalignment (cont.).

(a)

(b)

(c)

Figure 6: 2-D Magnetic flux distribution between the

coupled coils with core. (a) Perfect Alignment, (b) Planar

Misalignment, (c) Angular misalignment (d) Planar and

angular misalignment.

Performance Evaluation of Square Coupled Coils at Different Misalignments for Electric Vehicle Battery Charging

293

(d)

Figure 6: 2-D Magnetic flux distribution between the

coupled coils with core. (a) Perfect Alignment, (b) Planar

Misalignment, (c) Angular misalignment (d) Planar and

angular misalignment (cont.).

(a)

(b)

Figure 7: 2-D Magnetic flux distribution between the

coupled coils with core and chassis. (a) Perfect Alignment,

(b) Planar Misalignment, (c) Angular misalignment (d)

Planar and angular misalignment.

(c)

(d)

Figure 7: 2-D Magnetic flux distribution between the

coupled coils with core and chassis. (a) Perfect Alignment,

(b) Planar Misalignment, (c) Angular misalignment (d)

Planar and angular misalignment (cont.).

Figure 8(a), Figure 8(b) and Figure 8(c) give the

bar diagram of the MI values between the coupled

coil with perfect alignment without, with core and

with both core and chassis at all three cases of

horizontal distances and various vertical distance

and at 0° angular misalignments. Similarly,

Figure 8(d), Figure 8(e) and Figure 8(f) show the MI

values at 15° and Figure 8(g), Figure 8(h) and

Figure 8(i) at 30° angular misalignments.

From Figure 8 it is clear that the mutual

inductance decreases as the distance between the

coupled coils increases either in horizontally,

vertically or in angularly for both the cases such as

air core and ferrite core

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(a)

(b)

(c)

(d)

(e)

(f)

Figure 8: Graphical representation of MI vs Vertical

distances (a) 0° Misalignment (without core), (b) 0°

Misalignment (with core), (c) 0° Misalignment (with core

and chassis), (d) 15° Misalignment (without core), (e) 15°

Misalignment (with core), (f) 15° Misalignment (with core

and chassis), (g) 30° Misalignment (without core), (h) 30°

Misalignment (with core), (i) 30° Misalignment (with core

and chassis).

Performance Evaluation of Square Coupled Coils at Different Misalignments for Electric Vehicle Battery Charging

295

(g)

(h)

(i)

Figure 8: Graphical representation of MI vs Vertical

distances (a) 0° Misalignment (without core), (b) 0°

Misalignment (with core), (c) 0° Misalignment (with core

and chassis), (d) 15° Misalignment (without core), (e) 15°

Misalignment (with core), (f) 15° Misalignment (with core

and chassis), (g) 30° Misalignment (without core), (h) 30°

Misalignment (with core), (i) 30° Misalignment (with core

and chassis) (cont.).

5 CONCLUSIONS

This paper describes the inductive coupling

characteristics of the square coupled coils with

variations in distance between the coils vertically

and horizontally with different misalignment

conditions. Further it has been designed the

inductive coupled coils ferrite core and chassis. The

magnetic characteristics such as mutual inductance

is studied for different misalignments. It has been

concluded that by using ferrite core the magnetic

characteristics can be improved.

Table 1: Specifications of the Coils.

Description

Specifications

Number of turns in transmitter (N1)

Number of turns in receiver (N2)

Radius of the conductor

0.25 cm

Width of the coil

3cm

Inner length of the coils

4 cm

Ferrite core material

N96

Core dimensions

16*16*0.1 cm

Steel Chassis material

Stainless steel

Chassis dimensions

24*24*0.2 cm

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