Transportation systems play a vital role in this modern era. At the same time, it accounts for about 27% of the carbon emission. Carbon emission is crucial as it increases global warming to an alarming state. Global warming is a threat to human life, and at the same time, it leads to drastic changes in the climate.
Researchers, Policy makers, and Government authorities are working toward minimizing carbon emissions, and world leaders have made the Paris agreement for zero carbon emissions to reduce the effect of global warming. The burning of fossil fuels is the main reason for carbon emissions.
Fossil fuels are burnt for manufacturing fuels like petrol and diesel for transportation systems. Figure 1 shows the carbon emission statistics by different sectors globally.
Global Carbon Emission by Vehicle
Fig.1. Global Carbon Emission
Electric Vehicles are the best alternative to traditional transportation systems. Electric vehicles have almost zero emission, and it is becoming popular globally.
The size of the global electric vehicle market is expected to increase from 8,151 thousand units in 2022 to 39,208 thousand units by 2030.
Manufacturers have been obliged to offer Electric Vehicles globally because of factors including the rise in demand for low-emission transportation and government support for long-range, zero-emission vehicles through subsidies and tax breaks.
Market share of Electric Vehicles Globally
Fig.2 Electric Vehicle Market Share Globally
Advantage of Electric Vehicles Over ICE Vehicles
Comparatively, an Electric Vehicle has significantly reduced operating costs. Rather than using fossil fuels like gasoline or diesel to charge their batteries, Electric Vehicles use electricity. Due to their greater efficiency and lesser cost, an electric vehicle is more affordable than purchasing diesel or gasoline for your travel needs.
Electric vehicles are environmentally friendly when powered by renewable energy sources. If charging is done with the aid of renewable energy sources built at home, like solar panels, the cost of electricity can be further decreased. Because they have fewer moving parts than internal combustion engines, electric vehicles require significantly less maintenance.
As a result, operating an electric vehicle requires a low annual cost.
Despite all the advantages, EV users are facing critical problems in charging their vehicles as there is a lack of infrastructure facilities. Despite all the advantages, EV users are facing critical problems in charging their vehicles as there is a lack of infrastructure facilities.
By 2032, only 25% of the predicted overall number of public charging stations will actually exist at the current growth pace. The slow development of charging stations is partially caused by a severe shortage of lithium and other precious metals, which are necessary for EV chargers.
Thanks to wireless technology that makes EV charging effortlessly. There are two different types of wireless charging, Static wireless charging and Dynamic wireless charging. Now we will have an insight into them respectively.
To understand wireless charging we need to understand how wireless power transfer works.
What is a wireless power transfer (WPT) system?
Wireless power transfer (WPT), wireless power transmission, wireless energy transmission (WET), or electromagnetic power transfer is the transmission of electrical energy without wires as a physical link. (Source Wikipedia)
How does it work?
In a wireless power transmission system, a transmitter device, driven by electric power from a power source, generates a time-varying electromagnetic field, which transmits power across space to a receiver device, which extracts power from the field and supplies it to an electrical load. The technology of wireless power transmission can eliminate the use of wires and batteries, thus increasing the mobility, convenience, and safety of an electronic device for all users.
Wireless power transfer is useful to power electrical devices where interconnecting wires are inconvenient, hazardous, or not possible.
Types of EV Wireless Charging Technology
- Static wireless charging and
- Dynamic wireless charging
Static Wireless Charging System:
In the stationary wireless charging method, the vehicle charges under standstill conditions. Hence, we could easily park the EV at the designated parking space or in a garage that integrates with a wireless charging station.
The vehicle’s undercarriage carries the receiver, and the transmitter is installed underground. The transmitter and receiver get aligned before leaving the vehicle to complete charging. The distance between the transmitter and receiver, the size of their pads, and the AC supply power level all affect how long it takes to charge.
The optimal places to construct this static wireless charging station are those where EVs are parked for a certain period.
Fig.3 stationary wireless charging
Dynamic Wireless Charging System:
Dynamic wireless power transfer is an efficient method to alleviate range anxiety in electric vehicles and lower the price of onboard batteries. With pure electric vehicles, wireless charging is becoming popular. It allows charging even when the vehicle is moving.
In this method, a stationary transmitter transmits power over the air to the receiver coil in a moving vehicle. The continual recharging of its batteries while operating an EV on roads and highways could increase the vehicle’s trip range when employing Dynamically Wireless Charging System. The vehicle’s weight can be decreased as there is less necessity for massive energy storage.
According to operational techniques, there are four different categories of dynamic wireless charging systems, such as
- Wireless Capacitive Electric Vehicle Charging System
- Permanent Magnetic Gear Wireless Electric Vehicle Charging System
- The Inductive Wireless Electric Vehicle Charging System
- Resonant induction Electric Vehicle Charging system
Now we will discuss all such types in detail.
(i) Wireless Capacitive Charging Systems:
Systems for capacitive wireless power transfer can function effectively at much higher frequencies and don’t need ferrites. As a result, capacitive wireless power transmission devices can be smaller, lightweight, cheaper, more reliable, and simpler to embed in a road.
Furthermore, when compared to inductive wireless power transfer systems, capacitive wireless power transfer systems are more compassionate of nonlinearities. It is because electric fields are naturally more directed than magnetic fields.
Figure 4 depicts the structural layout of a capacitive Wireless Power Transfer System for EV charging. In this method, there are two pairs of conducting plates available. One pair of conducting plates are implanted in the road, and the other pair is mounted to the chassis of the vehicle. There is a significant air gap provided that separates the two pairs to achieve wireless power transfer. The inverter converts the dc input voltage into a high-frequency ac output. To increase the ac output voltage it is fed to the matching network.
This raises the voltage at the coupling plates’ roadside, allowing for significant power transfer with little displacement current. As a result, there exists a relatively lesser fringing field. A second resonant matching network ramps the current up (and the voltage down) to the amount necessary to charge the EV battery.
Furthermore, the capacitive reactance of the coupling plates is reactively compensated by both matching networks. A high-frequency rectifier connects the system to the EV battery in the end.
Fg.4 Wireless Capacitive Charging Systems for Electric Vehicles
(ii) Permanent Magnetic Gear Wireless Electric Vehicle Charging System
Charging systems based on coaxial cable, this approach uses two synced permanent magnets (PM) placed side by side. The transmitter winding receives the power, producing a mechanical torque in the primary PM.
Utilizing mechanical torque, the primary PM revolves and mechanically interacts with the secondary PM to exert a torque on it. The primary PM operates as the generator mode in a system with two synchronized PMs.
In contrast, the secondary PM collects power and transmits it to the battery via the power converter and Battery management system. However, there are numerous difficulties in using this technique in both static and dynamic systems.
As the coupling between the two synchronized windings drastically decreases, the power transmission potential is inversely proportional to the axis-to-axis dispersion between the primary and secondary PMs. Therefore, it might be applicable for stationary wireless charging systems but extremely difficult for dynamic applications.
Fig.5 Permanent Magnetic Gear Wireless Electric Vehicle Charging System
(iii) The Inductive Wireless Electric Vehicle Charging System
Nikola Tesla created the conventional Inductive Power Transfer in 1914 to transmit power wirelessly. It draws inspiration from various EV charging systems. Inductive Power Transfer has been tested and used to transfer contactless power from the source to the receiver. It is used in numerous applications, ranging from milliwatts to kilowatts.
The Chevrolet S10 EV released by General Motors (GM) in 1996, used the Magne-charge Inductive Power Transfer (J1773) system, which offered level 2 (6.6 kW) slow and level 3 (50 kW) fast charges. The primary coil of the magne-charge, also referred to as a recharging paddle (inductive coupler), was put into the vehicle’s charging port.
Here, the secondary coil was supplied with electricity and permitted to charge the EV. The University of Georgia exhibited a 6.6 kW Level 2 EV charger that could operate at a frequency of 77 kHz and charge batteries with voltages between 200 and 400 V.
A 10 KVA coaxial winding transformer provided significant benefits in this universal Inductive Power Transfer, including a flexible inductive coupling design and an easily modifiable power range.
Fig.6 Inductive Wireless Electric Vehicle Charging System
(iv) Resonant induction Electric Vehicle charging system
One of the most well-known and sophisticated types is the Resonant induction Power Transfer. Fig. 5 displays a block diagram of the Resonant induction Power Transfer for EVs. High-Frequency AC power is fed into the source and sent to the transmitter or main winding. Power is delivered to the secondary coil or receiver by varied metallic fields.
Additional power circuits and filter circuitry convert the received electricity to DC for the EVs’ battery bank. In addition to creating the resonant casing and reducing further losses, extra compensation networks in the series or parallel configurations are added to both the primary and secondary windings as against the typical Resonant induction Power Transfer.
Effective power transfer is possible when the primary and secondary resonant frequencies are used in conjunction. The Resonant induction Power Transfer operates at frequencies between tens of kilohertz to several hundred kilohertz.
The magnetic flux created at this frequency range in the absence of a magnetic core harms mutual inductance, and thus the coefficient of coupling. Due to the EVs’ 150–300 mm minimum height clearance requirement, the coupling coefficient in the Resonant induction Power Transfer ranges from 0.2 to 0.3. Strong coupling between the primary and secondary coils would result in a higher mutual inductance value, and vice versa.
Many different constructions use magnetic ferrite cores to enhance the wireless transformer’s coupling coefficient design.
Fig.7 Resonant induction Electric Vehicle charging system
Wireless charging is one of the most convenient charging infrastructures in Electric Vehicles. It is expensive, but still attracts a lot of researchers.
Because Electric Vehicles can operate for many hours without stopping for recharging, they will become really autonomous. Perhaps the most exciting aspect is that EVs equipped with wireless charging technology en route can have substantially smaller batteries. As a result, this technology decreases the environmental effect as well as the cost of electric vehicle adoption.