Ki Cordless Kitchen: high-power wireless power transfer requires new power electronics

With the introduction of the Ki Cordless Kitchen standard, the Wireless Power Consortium (WPC)[1] a next, technically challenging step in the evolution of wireless energy transfer.

While Qi and Qi2 are limited to efficiently charging batteries in the power range of up to a few tens of watts, Ki is designed for direct power transfer up to 2.2 kW. This makes wireless power for kitchen appliances such as kettles, blenders, and food processors a reality.

During the Power Electronics & Energy Storage 2026 event, Will Ettes, senior designer power electronics at Philips, will provide an in-depth explanation of the power electronic consequences of this standard. His presentation makes it clear that Ki is not merely an upscaling of Qi, but requires a fundamentally different system design.

From charging to direct feeding

A crucial difference compared to earlier WPC standards is that Ki does not store energy in a local battery. The wirelessly transmitted power feeds the load directly: heating elements, motors, and power electronics are driven without a buffer. This places high demands on the stability and dynamics of the system, especially during the rapid load variations typical of household appliances.

In addition, Ki was explicitly set up as interoperable standard. Transmitters and receivers from different manufacturers must work together reliably, which means that the power electronics must withstand a wide range of mechanical and electrical conditions.

Wide spread in magnetic coupling

One of the biggest technical challenges Will mentions is the variation in magnetic coupling between transmitter and receiver. In a kitchen environment, the distance between the coils depends heavily on the thickness of the worktop. Distances of 15 to 40 mm are realistic, while the diameter of the receiver coil varies between 8 and 18 cm.[2]

The result is an exceptionally wide range in coupling factor, from approximately k = 0.15 to 0.75. For designers, this means that voltage, current, and resonance conditions can shift over a broad spectrum, while the output power must remain constant.

Load-resonant inverter topologies

To make this problem manageable, Ki uses load-resonant inverter topologies. By positioning the resonance on both the transmitter and receiver sides, the system can handle variations in coupling and load more efficiently. At the same time, favorable switching conditions, such as zero-voltage switching, are maintained over a wide operating range.

According to Will, this choice is essential to keep both efficiency and thermal and electromagnetic margins within acceptable limits at kilowatt power levels. Moreover, the load-resonant approach offers more freedom in the magnetic design of coils and ferrite structures.

layered rule strategy

A second key to robust operation is the combination of multiple control mechanisms. The Ki standard supports:

• Duty cycle control for precise power setting around nominal coupling;
• Frequency control to compensate for shifting resonance points;
• Burst mode control for stable operation under low load or adverse coupling.

This multidimensional approach makes it possible to keep the system stable across the entire power and torque factor range, while limiting EMC emissions and component stress.

Safety and EMC as a prerequisite

In addition to efficiency, safety plays a central role in the Ki design. Power transfer starts exclusively after digital handshaking between transmitter and receiver. If the device is moved or tilted, the power is switched off immediately. This makes Ki intrinsically safe, even at high power levels.

For power electronics designers, this means that power regulation, communication, and safety cannot be viewed in isolation. EMC compliance in a domestic environment is an explicit design requirement, not a rework.

Relevance for the designer

The Ki Cordless Kitchen standard is therefore more than a consumer innovation. It is a practical example of high-power inductive energy transfer in a complex, realistic application. The insights from Will Ettes’ presentation are directly relevant to designers working on resonant converters, wireless energy transfer, or power electronics in variable system environments.

Ki demonstrates that wireless energy transfer at the kilowatt level is technically feasible, provided that topology, magnetic design, and control strategy are approached integrally. For power electronics, the kitchen thus unexpectedly constitutes a high-end application.

Want to know more? Will Ettes will give the closing plenary lecture at Power Electronics & Energy Storage on May 27, 2026. View the program and register at the website.

[1] Home | Wireless Power Consortium

[2] The Ki Cordless Kitchen standard – FHI, Federation of Technology Branches