Eggtronic Enables GaN-based Charging for EVs
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A patented AC wireless power hybrid technology from Eggtronic is designed to increase the power and efficiency of wireless charging applications for home and automotive applications.
Igor Spinella, CEO and founder of Eggtronic, said the proprietary technology dubbed E2WATT is supported by a GaN half-bridge and a dsPIC33 microcontroller. That arrangement merges a conventional power adapter and Qi wireless transmitter, boosting efficiency to overcome challenges posed by the Qi wireless power transfer standard.
Traditional Qi wireless power is limited by distance (usually 5 mm), and maximum power (up to 30 W). Overheating is another issue: After fast-charging, thermal protections are activated, which stops charging. “Our solution directs the magnetic field in the right way, avoiding the problem of overheating not only for the Qi standard but also offering compatibility with the new Apple 12, which is not Qi-certified, thus paving the way not only for automotive but also for consumer applications,” said Spinella.
As electric vehicles merge into the fast lane, technology development is shifting to critical areas ranging from enhanced power management to faster charging schemes. All will help reshape power grids. We go under the hood in our upcoming Electric Vehicle Special Project.
He added that the new hybrid technology with AC input does not require an AC/DC adapter, allows up to 95 percent efficiency with power of up to 300 W and 40-mm distances while reducing the overall size thanks to GaN technology. “The powers can be scaled up, reproducing the applicability for large-scale applications such as electric vehicle charging. Ninety-five percent was achieved at a distance of 10 mm, which is double what we could achieve with the Qi standard, [and] which at 5 mm is usually no more than 70-percent efficient, representing a real breakthrough for inductive standards,” Spinella claimed.
Qi Standard
The Qi system for wireless power transfer consists of two basic modules, base station and mobile device, as shown in Figure 1. The base station includes one or more power transmitters capable of providing wireless power transfer. It consists in principle of a power conversion and a control and communication units. The various subsystems have analog features responsible for driving a primary coil and digital features controlling the power transfer process while communicating with other parts of the system.
The mobile device includes a single power receiver which consists of a power-harvesting and a control and communication units. On the same level as the transmitter are analog and digital subsystems for process optimization. The actual power transfer from the base station to the mobile device is achieved by inductive coupling between the two primary and secondary coils: once placed in close proximity, these coils create a resonant transformer in the air with resonant frequencies on the order of 100 kHz. The power transfer is constantly monitored and controlled by system logic for varying power requirements imposed by the device depending on its current state. (For example, the completion of a battery charging process.)
The technology currently enables wireless power transfer of up to 30 W with an operating frequency of 100-200 KHz over a distance of up to 5 mm.
E2WATT Technology
With around 200 patents and founded in 2012, Eggtronic specializes in energy conversion and wireless power. It has recently focused on various consumer designs through inductive and capacitive approaches. The company has already raised more than $20 million.
“On the basis of the Qi standard, we are already serving many automotive companies,” Spinella said. “We decided to increase the level of integration of our solutions in order to launch our proprietary standards [that are] able to increase performance and features. Thus, we developed our own ASIC, entirely designed by us and manufactured by TSMC.”
E2WATT is its latest wireless technology (see Figure 2). It is powered directly from AC without the need for an external power supply. The hybrid wireless AC power approach serves as both power supply and wireless charger. “The goal was to get a product that could be better than the equivalent wired power supply unit. It is certified as a power supply from an emissions and safety point of view, and of course, it is a wireless power transfer technology,” said Spinella.
E2WATT uses GaN technology from Navitas Semiconductor, highlighting silicon’s inability to provide adequate switching frequencies, for example, which is limited to about 100 KHz. The harder it is driven, the more heat generated, along with complexity and cost. Meanwhile, low-frequency magnetics are too slow when running at corresponding speeds. “Hard-switching” topologies are one option, but they introduce switching losses; when frequency is increased, efficiency drops due to increased parasitic inductance.
Also, old topologies and legacy control ICs can’t keep up. Therefore, the first step is attempting to solve the switch problem using GaN technology. Navitas’ GaNFast approach consists of a GaN switch – a field-effect transistor – with monolithically integrated analog drive circuits and digital logic circuits integrated on the same chip as the GaN power device. GaNFast power ICs are rated at 2 MHz. High-speed operation offers reductions in size and the cost of power conversion for fast-charging systems.
In addition to GaN technology, Microchip Technology’s dsPIC33 microcontroller with u core DSP, high-speed ADC and high-resolution pulse width modulation enables the E2WATT’s digital architecture to offer feedback control of the transmission while optimizing the charging distance. Thanks to its proprietary receiver technology, Spinella said the platform enables a significant drop in receiver temperatures.
The E2WATT transmitter (Figure 3) uses logic to convert AC power from the grid into another AC frequency to activate the coil. The base consists of half-bridge circuit by Navitas to stimulate the LC tank, which complies with the Qi standard. The architecture allows for direct high-input voltage, eliminating the need for an AC/DC converter in series, and for zero-voltage switching (ZVS) without the use of the resonant LC tank, ensuring that ZVS is achieved in most load conditions. It also allows for continuous control from light to full load, without using burst mode, said Spinella.
ZVS also reduces the capacitive switching losses at turn-off, and turn-on, thereby eliminating the capacitive turn-on loss. That makes it suitable for high-frequency operation.
The receiver acts both as a rectifier and as a non-dissipative regulator. This is achieved by controlling the ratio between active power delivered to the load and reactive power reflected to the primary side. “The reactive power in the wireless system [transmitter and receiver] is minimized using a second-control loop that ensures minimum reactive energy in the system, Spinella added.
Wireless charging is undeniably faster, easier and more convenient than wired alternatives. Not only is it more efficient, but also provides better thermal performance. The latter is often seen as a secondary design consideration by developers in order to bring their products to market faster.
Electric cars are large energy stores, and the ability to provide more power with less frequent charging is a short-term goal to support EV adoption. Larger battery size, the higher the rate of current flow and heat generation are also considerations. Therefore, integrating technology into electric cars and installing municipal and private charging stations could eventually reduce the need to connect vehicles for charging.
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