**Abstract**

Wireless Power Transfer (WPT) technology can transfer electrical energy from a transmitter to a receiver wirelessly. Due to its many advantages, WPT technology is a more adequate and suitable solution for many industrial applications compared to the power transfer by wires. Using WPT technology will reduce the annoyance of wires, improve the power transfer mechanisms. Recently, the WPT gain enormous attention to charging the on-board batteries of the Electric Vehicle (EV). Several well-known car manufacturing companies start efforts to adopt WPT technology and enhance its features. Therefore, WPT can be achieved through the affordable inductive coupling between two coils named a transmitter and a receiver coil. In EV charging applications, transmitter coils are located underneath the road, and receiver coils are installed in the EV. The inductive WPT of resonant type is generally applied to medium-high power transfer applications like EV charging because it achieves better energy efficiency. In this chapter, various WPT technologies are discussed and tested in EV wireless charging applications. Furthermore, extensive information is given to developing an advanced WPT technology that can transfer maximum power by achieving maximum efficiency.

**Keywords:** Wireless Power Transfer (WPT), Electric Vehicle (EV), Energy Efficiency

## **1. Introduction**

A Wireless Power Transfer (WPT) is one of the promising technologies used to transfer electric energy from a transmitter to a receiver wirelessly. WPT is an attractive solution for many industrial applications due to its enormous benefits over wired connections. The advantages include the no hassle of carrying wires, easy charging, and smoot of power transmission even in unfavorable environmental circumstances.

The idea of wireless power transfer (WPT) was first introduced at the end of the 19th century by Nicola Tesla. He manufactured a wireless lighting bulb that was used to receive electrical charge wireless [1]. Tesla used two metal plates that were closely placed to each other. A high-frequency Alternative Current (AC) potentials were passed between these two plates, and the bulb powered ON. However, some of the issues appeared while using WPT technology. One of the main issues is that the minimum power density and low transfer efficiencies affect when the distances increase. As a result, the performance of WPT technology becomes very slow. Therefore, the WPT technology is improved and used "strong coupled" coils when the distance increases more than 2 m while charging wirelessly [2]. The two

important WPT technologies are Inductive Power Transfer (IPT) and Capacitive Power Transfer (CPT). CPT is only applicable to low power applications with very short air gaps between 10–4 and 10–3 m, whereas IPT can be used for large air gaps around several meters, and its output power is much higher than CPT.

**Figure 1** Compares between CPT and IPT, **Figure 1a** shows the power transfer capability versus gap distance with efficiency values. Furthermore the figure indicates both IPT and CPT can achieve ≥90% efficiency at kilowatt power levels in their respective gap ranges. **Figure 1b** plots the transmitter/receiver area versus throughput power with efficiency. The coupler area is the cross-sectional area through which magnetic or electric fields transfer energy. **Figure 1c** plots the output power density (output power divided by the gap volume) versus frequency [3]. WPT technologies can be applied in television, phone chargers, and induction heating, medical devices, pacemakers, radiofrequency identification, sensors, robotics, and deeply used in wireless charging for EV [4–11].

In CPT and IPT power transfers, the respective energy stored in a unitary volume of space is

$$W\_{\varepsilon} = \frac{1}{2} \varepsilon\_0 E^2 \tag{1}$$

$$W\_m = \frac{1}{2}\mu\_0 H^2 \tag{2}$$

can help reduce the battery pack size and in turn make the EVs more proficient. However, all this cannot be knowledgeable by using traditional inductive chargers and WPT charging through large air gaps and least possible human interaction are

*Relationship between Ampere's law, Faraday's law, Maxwell's equations, inductive-coupling WPT, resonance-*

WPT systems are primarily classified as microwave, evanescent wave, magnetic resonance, electrical resonance, or electromagnetic induction methods. Scientists have newly proposed an electromagnetic induction method that is not premised on transformer coupling. It is revealed that the electric power transmission over a range including a magnetic field resonance method is enabled by adopting this method [13]. Ampere's law, Faraday's law, Maxwell's equations, the inductive-coupling WPT, the resonance-coupling WPT, and WPT via radio waves are the major theory that can describe the functionality of WPT technologies. **Figure 2** shows this relation-

When AC or DC electrical energy is transformed to high-frequency electrical energy by using a high-frequency inverter, the wireless feeding device (Tx.) releases electrical energy through a transmission device into space. Then, the

required [12].

**31**

**Figure 2.**

ship between these theories.

**2. Basic theory of WPT system**

*coupling WPT, and WPT via radio waves [13].*

*Wireless Power Charging in Electrical Vehicles DOI: http://dx.doi.org/10.5772/intechopen.96115*

where *E* and *H* are the intensity of the electric and magnetic fields and, *ε*<sup>0</sup> and *μ*<sup>0</sup> are the permittivity and the permeability of the free space.

Health and safety, and economic impact are the critical points that should be considered in any technology of WPT for charging EVs or in any other applications. WPT technology for charge replacement, EVs can become gorgeous option. WPT charging has the advantage that it can make the charging process automated, suitable and safe for users and large scale introduction of WPT charging infrastructure

#### **Figure 1.**

*Comparison between CPT and IPT technologies [3], (a) gap distance and output power with efficiency value , (b) coupler area and output power with efficiency value, (c) frequency and output power density with efficiency value.*

#### **Figure 2.**

*Relationship between Ampere's law, Faraday's law, Maxwell's equations, inductive-coupling WPT, resonancecoupling WPT, and WPT via radio waves [13].*

can help reduce the battery pack size and in turn make the EVs more proficient. However, all this cannot be knowledgeable by using traditional inductive chargers and WPT charging through large air gaps and least possible human interaction are required [12].

WPT systems are primarily classified as microwave, evanescent wave, magnetic resonance, electrical resonance, or electromagnetic induction methods. Scientists have newly proposed an electromagnetic induction method that is not premised on transformer coupling. It is revealed that the electric power transmission over a range including a magnetic field resonance method is enabled by adopting this method [13].

Ampere's law, Faraday's law, Maxwell's equations, the inductive-coupling WPT, the resonance-coupling WPT, and WPT via radio waves are the major theory that can describe the functionality of WPT technologies. **Figure 2** shows this relationship between these theories.

## **2. Basic theory of WPT system**

When AC or DC electrical energy is transformed to high-frequency electrical energy by using a high-frequency inverter, the wireless feeding device (Tx.) releases electrical energy through a transmission device into space. Then, the

receiving system (Rx.) converts the electrical power into DC in the recipient electrical apparatus. In addition, the efficiency of the electrical power transmission, medical and environmental influence of electromagnetic waves, and improvement the facile high speed charging, safe security, and energy storage density are essential limits should be considered when WPT is designed for EVs.

**Type Coupling mechanism Resonant**

*Wireless Power Charging in Electrical Vehicles DOI: http://dx.doi.org/10.5772/intechopen.96115*

1 Electrostatic induction

2 Coupled-resonant using electrostatic induction

3 Coupled-resonant with self-resonant coupler (E-field dominant)

4 Far-field type

**Table 1.**

**Figure 5.**

**33**

*Block diagram of WPT system.*

Coupled-resonant using magnetic induction

Coupled-resonant with self-resonant coupler (H-field dominant)

(microwave WPT)

**E-field H-field**

Yes No Power factor

impedance Magnetic induction No Yes

Dominant Negligible Discrete

Dominant

Negligible Dominant

Dominant Small, but not negligible

Coupling in far-field. Ratio of E-field to Hfield is 377 Ω

Small, but not negligible

**mechanism**

compensation may be considered as a resonant circuit

reactance device is necessary for resonance

Coupler acts as resonator

Tx and Rx antennas resonate independently

*Coupling mechanism, resonant mechanism, and impedance matching mechanism for various kinds of WPT.*

Tx/Rx antennas are matched to the source/ load independently

**Impedance matching mechanism (feeding mechanism)**

Not active following for load

According to the load impedance or transmission distance, active following by circuit parameter in impedance matching circuit or transmission frequency is necessary to achieve simultaneous conjugate matching

**Schematic**

WPT systems are classified as microwave, evanescent wave, magnetic resonance, electrical resonance, or electromagnetic induction methods. **Figure 3** shows the relation between transmitted power and transmitted length of these methods for WPT systems. Additionally, WPT can be classified to the kind of Type 1,Type 2, Type 3 and Type 4 as shown in **Figure 4**. **Table 1** shows the relationship of Types 1–4 from the viewpoint of coupling mechanism, resonant mechanism,

**Figure 4.** *Relationship of different kinds of WPT scheme.*

*Wireless Power Charging in Electrical Vehicles DOI: http://dx.doi.org/10.5772/intechopen.96115*


#### **Table 1.**

*Coupling mechanism, resonant mechanism, and impedance matching mechanism for various kinds of WPT.*

**Figure 5.** *Block diagram of WPT system.*
