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Exploring Various Wireless Charging Methods for Electric Vehicles

Published on 07th June 2023

Inductive charging for electric vehicles or EVs is one of the two widely used wireless charging methods for EVs. It uses electromagnetic fields to transfer energy from the charging station to the EV. 

 

Contrary to the traditional plug-in charging method, inductive car charging is far more convenient, safe, and energy-efficient. It is still under development and economy of scale is yet to be achieved. However, looking at the current pace of its development, there is a certainty that the wireless EV charging system is going to revolutionize EV charging systems.

 

In this blog post, we will understand how inductive charging is already making an important stride toward becoming the de-facto EV charging method.

 

Let’s understand the basic concept of wireless EV charging.

 

What is wireless EV charging?

Wireless EV (electric vehicle) charging is an innovative technology that allows electric vehicle owners/drivers to charge their vehicles without any physical cables or connectors. Wireless charging is definitely a game-changer for the still-growing EV industry.

 

Electric vehicles typically require many hours for full charging (without high-powered charging stations). However, dynamic wireless charging technology eliminates that requirement by delivering power even when the vehicle is on the move "on the road by the road" and when the vehicle is moving above the path of transmitters.

 

How does wireless EV charging work?

The basic principle of wireless charging is the same as the transformer working principle. In wireless charging there are a transmitter and receiver, 220V 50Hz AC supply is converted into High frequency alternating current, and this high-frequency AC is supplied to the transmitter coil, then creates an alternating magnetic field that cuts the receiver coil and causes the production of AC power output in the receiver coil. 

 

But the important thing for efficient wireless charging is to maintain the resonance frequency between the transmitter and receiver. To maintain the resonant frequencies, compensation networks are added on both sides. Then finally, this AC power at the receiver side is rectified to DC and fed to the battery through Battery Management System (BMS).

 

Source: https://core.ac.uk/download/pdf/145233488.pdf

 

The charging station has a coil of wire that generates a magnetic field. When the vehicle is parked over the charging station, the magnetic field induces a current in the vehicle's coil, which charges the battery.


Before understanding the more advanced wireless EV charging, let's understand the traditional electric vehicle charging methods.


Traditional EV charging methods


Charging through a cable (Manual plug-in charging)

 1 - 230 Volts socket (AC) limited to 2.3 kW (1-phase, 10A)

 

 2 - 230 Volts socket (AC) entails charging through In-Cable Control Box (ICCB). 7.4 kW, capacity of max. 7.4 kW can be (1-phase, 32A) or 22 kW (3-phase, 32A)

 

 3 - The adequate charging capacity (AC) is determined by communication between the charging station and the vehicle.  11 kW, 22 kW, or sometimes 43 kW (>22 kW = fast charging).

 

 4 – DC charging (Fast charging), from 50 kW to 175 kW


Charging by means of a pantograph

Charging by pantograph delivers a high transfer of energy in a short time (typically 5-10 mins) through conductive transfer. Heavy-duty vehicles like electric buses, trucks, and special vehicles work on pantograph technology for fast charging. There are two types of pantograph charging to deliver power for EVs.

 

Top-down or inverted pantograph




Rooftop pantograph




Wireless EV Charging (WCS)

Wireless charging systems charge electric vehicles by using electromagnetic fields to transfer energy. Wireless charging for electric vehicles can be distinguished into two categories:

 

Static Wireless Charging

 


                                                                                                                                                                                                      Source - Qualcomm

In this type of wireless charging system, the vehicle gets charged when it is parked (static mode) above the transmitter, with the receiver arranged underneath the vehicle. Importantly, the vehicle receiver needs to be aligned over the transmitter to transmit power through the air gap. Charging time depends on the power supply level, distance (air gap) between the transmitter and receiver, and their sizes.  


Dynamic Wireless Charging (DWC system)

 

In this type of wireless charging system, the vehicle gets charged while in motion. How it works is that power is delivered from a stationary transmitter to the receiver coil in a moving vehicle. With Dynamic wireless charging systems (DWCS), range anxiety typically experienced by drivers of electric vehicles can be minimized with the continuous charging of its battery while driving on DWCS-enabled roads. Further, this type of system removes the need for large battery storage, allowing a steep drop in vehicle weight and improving overall efficiency as a result. 
 

Understanding the different types of wireless charging

Capacitive Wireless Charging System (CWCS)

Wireless transfer of energy between transmitter and receiver is accomplished by means of displacement current caused by the variation of the electric field. Instead of magnets or coils as transmitters and receivers, coupling capacitors are used here for wireless transmission of power. The AC voltage is first supplied to the power factor correction circuit to improve efficiency and maintain the voltage levels and reduce the losses while transmitting the power. 

 

Then it is supplied to an H-bridge for the High-frequency AC voltage generation and this high-frequency AC is applied to the transmitting plate which causes the development of an oscillating electric field that causes displacement current at the receiver plate by means of electrostatic induction.

 

The AC Voltage at the receiver side is converted to DC to feed the battery through BMS by rectifier and filter circuits. Frequency, voltage, size of coupling capacitors, and air gap between transmitter and receiver affect the amount of power transferred. Its operating frequency is between 100 to 600 KHz.

 

Permanent Magnet Gear Wireless Charging System (PMWC)

Here transmitter and receiver each consist of armature winding and synchronized permanent magnets inside the winding. At the transmitter side operation is similar to motor operation. When we apply the AC current to transmitter winding it induces mechanical torque on the transmitter magnet causing its rotation. 

 

Due to the magnetic interaction change in the transmitter, the PM field causes torque on the receiver PM which results in its rotation in synchronous with the transmitter magnet. 

 

Now change in the receiver's permanent magnetic field causes the AC current production in winding i.e., the receiver acts as a generator as mechanical power input to the receiver PM converted into electrical output at receiver winding. The coupling of rotating permanent magnets is referred to as magnetic gear. The generated AC power at the receiver side is fed to the battery after rectifying and filtering through power converters.

 

Inductive Wireless Charging System (IWC)

The basic principle of IWC is Faraday's law of induction. Here wireless transmission of power is achieved by mutual induction of a magnetic field between the transmitter and receiver coil. When the main AC supply is applied to the transmitter coil, it creates AC magnetic field that passes through the receiver coil and this magnetic field moves electrons in the receiver coil and causes AC power output. 

 

This AC output is rectified and filtered to Charge the EV’s energy storage system. The amount of power transferred depends on frequency, mutual inductance, and distance between the transmitter and receiver coil. The operating frequency of IWC is between 19 to 50 KHz.

 

Resonant Inductive Wireless Charging System (RIWC) 

Basically, resonators having high-Quality factors transmit energy at a much higher rate, so by operating at resonance, even with weaker magnetic fields we can transmit the same amount of power as in IWC. The power can be transferred to long distances without wires. Max transfer of power over the air happens when the transmitter and receiver coils are tuned i.e., both coil's resonant frequencies should be matched.

 

So to get good resonant frequencies, additional compensation networks in the series and parallel combinations are added to the transmitter and receiver coils. These additional compensation networks along with improvement in resonant frequency also reduce the additional losses. The operating frequency of RIWC is between 10 to 150 KHz.

 

How will wireless electric vehicle charging change the automotive industry?

The advent of wireless charging enables an array of opportunities and new markets, which are yet to rise. From autonomous taxis to cargo transport without halt, innovative transporting methods are possible. Wireless charging EV also allows users to can avoid getting out of the vehicle in extreme weather conditions to charge the vehicle. 

 

Investment in wireless EV charging

Currently, investments are being sought to develop dynamic wireless charging that also allows data transfer between the road and the vehicle, which gives the users access to multiple types of data like entertainment, weather conditions, and traffic conditions. The consumer will be billed based on the amount of energy consumed. Smart roads with autonomous driving technology also pave the way for motor homes (trailers attached to vehicles) within a decade.

 

The Swedish government has prepared a project road map for an electrified road. The plan includes the construction of 2,000 kilometers of an electrified road on a high-speed highway for dynamic charging of electric trucks at an estimated cost of USD 3 billion.

 

The UK plans to spend GBP 40 million on electric vehicle charging infrastructure and wireless charging roads (dynamic charging) to push the country towards better air quality. The government plans to develop both on-street and wireless charging to help transition from internal combustion engine cars to electric and hybrid. The WCS will be installed on residential streets, car parks, and taxi ranks across Greater London, the Midlands, and Scotland and will become operational by June 2020.

 

The OEMs and governments are emphasizing and incentivizing electric vehicle usage and sales to reduce tailpipe emissions. Countries like China are cornering consumers to buy electric vehicles with many schemes and quotas. With the increase in demand for electric vehicles, the requirement for charging stations would increase.

 

EV wireless charging companies

The wireless charging market is dominated by start-ups and large market participants. Some of the key players include Qualcomm Inc., Fulton Innovation LLC, Texas Instruments, Inc., WiTricity Corporation, Convenient Power HK Ltd., Integrated Device Technology, Inc., Energizer Holdings, Inc, and Oregon Scientific, Inc.

 

Drawbacks of wireless charging technology for EVs

There are also some downsides such as considerable potential energy loss (5% - 9%), and the high cost of the infrastructure, making it uneconomical for many governments and residential consumers (average Tesla wall connector ranges from USD 1200 to USD 2000 while the wireless charge costs up to USD 3000 for the same rated power). The initial stages of wireless charging are restricted to densely populated urban areas and limit the consumers to a predefined location. There might (not proved) also be minor health effects due to the long-term exposure to magnetic fields in the case of dynamic charging.

 

Conclusion

The auto industry is moving into a phase where electric vehicles keep on increasing the market share, forcing OEMs to meet emission standards. Though ICE (Internal Combustion Engine) vehicles will continue to dominate the market for several years, in the long-term BEVs are set to dominate. As the transition unfolds, ICE vehicles will begin to decline in share from the current 95% of the global level to about half of all vehicles by 2030-2035, with the other half of the market made up of HEVs, PHEVs, and BEVs.

 

The wireless electric vehicle charging market has vast potential as the future is dominated by autonomous vehicles, with many countries planning to ban ICE vehicles by 2030 to speed up the adoption of electric vehicles.

 

Huge investments in R&D for wireless charging forecasts a significant decrease in the price of the system with improved charge speed. Some of the huge barriers to the adoption of the electric vehicle such as range anxiety can be solved by dynamic charging, which shows the future of electric vehicle charging belongs to inductive charging.

 

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