Research: Tunable Power Management for Wireless EV Charging

Researchers from Drexel University’s College of Engineering, along with other collaborators, co-developed and tested a charging system that adjusts the delivery of an inductive charge to electric vehicles (EVs).

The method provides a solution for misalignment during EV charging and can accommodate various battery charge levels. The research was reported in the journal IEEE Transactions on Industrial Electronics.

 

 

Image used courtesy of Pixabay

 

What Is Inductive Charging?

Inductive charging is a way of wirelessly transmitting electricity from a power source to a device. The technology behind inductive charging is based on electromagnetic induction. In an automotive context, the power source (or charging pad) generates electricity and sends it through coils in the charger, which creates an alternating magnetic field. A receiver coil in an EV can then convert this alternating magnetic field into direct current (DC) electricity which can be used to charge batteries or run lights, for example.

Wireless charging of EVs is an attractive option because drivers do not even have to leave their car to charge up, cables are not needed, there are no emissions, and there is the potential for entire roads to have wireless charging built in. This means that charging could be available all the time and on the go.

However, wireless charging is not considered as efficient as wired charging. The electromagnetic interference from the charger can also affect other electronic devices that are close by. Additionally, misalignment of an electric vehicle with the charging can mean that the car simply does not get charged.

 

The Wireless EV Charging System Research

The charging system was built to the standards for wireless EV chargers set by the Society of Automotive Engineers (SAE). An adjustable resistor regulates the battery charge levels, and a moveable platform allows for up to 100mm of misalignment between the transmitter and charging coils.

In an interview with EE Power, a lead researcher of the study, Assistant Professor Fei Lu of Drexel’s Department of Electrical and Computer Engineering explained, “A major motivation is to continuously regulate the power of a wireless charger based on the battery charging profile. In practical applications, the lithium-ion battery pack requires a specific charging process to maintain a high charging efficiency and a long lifetime.”

He continued, “However, the existing wireless power transfer (WPT) system is difficult to tune to satisfy the charging requirements. Usually, multiple power electronics converters are necessitated at the front-end of a WPT system to provide the capability to step-up and step-down the voltage. Especially when the misalignment between transmitter and receiver is included, the input voltage range varies widely. This increases the complexity of a WPT system.”

 

Image used courtesy of Drexel University

 

“This paper proposed to simultaneously tune the voltage and frequency of a WPT system that can continuously regulate the system power to satisfy the battery charging requirements. In this way, the voltage tuning range is reduced, and the frequency tuning range is within the SAE-J2954 standard,” Lu added.

The charging system was tested on partially charged and uncharged batteries under well-aligned and misaligned conditions. By tuning both the voltage and frequency of the charging process, the system provided a power input from 0 to 3.3 kilowatts (kW). This is the standard charging range for plug-in EV charging.

Under well-aligned and misaligned conditions, the researchers achieved nearly 96% efficiency. This is on par with commercial wireless chargers and just below what is capable of plug-in chargers.

“Most importantly, we proposed a parameter design methodology that can be extended to different systems at different power levels with different coupler structures,” Lu said. “For other systems, our method is also helpful to improve the charging performance.”

 

The Wireless EV Charging System Future

Lu expressed his desire to bring this wireless EV charging technology into the commercial space in the future.

“I plan to collaborate with industry partners for potential commercialization. There are multiple other applications, such as smartphone and laptop charging that may also require a large misalignment. One other application is the autonomous ground vehicle (AGV) in the warehouse. This technology can be extended to support dynamic charging to AGVs that can ensure they are charged even when they are moving along the track”.

 

Feature image used courtesy of Unsplash