Wireless Power Consortium Adds Resonant Extension to Qi Charging Spec

Despite the Wireless Power Consortium’s announcement last week that it has integrated resonant technology into the Qi specification for wireless power, the industry is no closer to a unified wireless power standard, John Perzow, Consortium vice president-market development, told Consumer Electronics Daily. “I wish it did,” Perzow said, when we asked if the addition of resonant technology opened the door to a unified standard down the road, but “it does not."

The industry’s three wireless charging specifications -- marketed as Qi, PMA (Power Matters Alliance) and Rezence -- have a significant amount of overlap among member companies, but the wireless charging technology is not interoperable, Perzow said. “They don’t communicate with each other, they don’t work with each other,” and “the details make it impossible for them to be interoperable,” Perzow said.

IHS Technology analyst Ryan Sanderson predicted that over the next few months companies that have been using magnetic resonance technology “will be trying to use it in a different approach to existing solutions” that use inductive charging where charging elements need to be aligned. He predicted a divide in use cases between the different inductive and resonance-based wireless charging rather than a “one-size-fits-all” solution. Inductive wireless charging, where charging coils have to couple, will continue to be useful in vehicles, for example, where keeping a smartphone in a stable position is important for safety. “In those instances, it makes sense to use a tightly coupled solution anyway,” he said.

Furniture embedded with wireless charging requires a resonance-based offering where charging coils don’t need to be coupled, Sanderson said. “I think we're going to begin to see use cases where it might make sense to use one technology over another,” he said. But consumers who want to charge a phone at a Starbucks using a resonance-enabled charging surface and then power up in a car with an inductive Qi charger would have “a problem,” he said. “There isn’t currently an interoperable solution, or the industry isn’t working in an interoperable way at the moment,” he said.

But the situation could be easing, Sanderson said, with the recent announcement that GM plans to support Powermat (PMA) and other wireless charging standards in its 2015 vehicles, which would eliminate the need for consumers to choose a standard based on the charging technology in their vehicle. “We're beginning to see solutions that are bridging that gap and offering multi-support,” Sanderson said. “Hopefully it will prompt others to look at similar solutions either on the transmitter side, or it could also prompt building … multi-mode receivers so they can work on different transmitters as well,” he said. Multi-mode transmitters and receivers would be a way to offer “interoperability to the consumer without their knowing that there are all these different standards out there,” he said.

IHS, meanwhile, forecasts that 50 million wireless charging-enabled mobile phones will ship this year and that adoption of in-cabin wireless power transmitters supporting multiple standards will pick up next year. Adoption is predicted to accelerate further as the infrastructure supporting multiple standards expands, Sanderson said. “Consumer and OEM frustration and confusion over incompatible wireless charging solutions” -- driven by the competing standards -- “will ease as multi-standard solutions develop further,” Sanderson said.

The Alliance for Wireless Power (A4WP) announced last week (CED July 29 p4) that its Rezence Baseline System Specification Version 1.2 was available to the public, and Perzow conceded that the announcement from Wireless Power Consortium, along with the impending arrival of Rezence wireless charging products on the market, was part of the reason for the timing of the announcement about the integration of resonance charging into the Qi spec. The fledgling A4WP consortium has positioned its Rezence charging standard as the one offering “spatial freedom” because of its resonance charging method that doesn’t require as precise positioning as the inductive charging method used by Qi. Inductive charging has a maximum distance of about 7 mm between transmitter and receiver versus 35-45 mm for resonant chargers, Perzow said.

But Perzow said the Qi standard has always had resonant capability. “A4WP distinguishes themselves as the only ones with resonance, but that’s not true,” Perzow said. Technically, he said, the inductive spec Qi is a resonant technology “but it’s not tuned.” He said resonant charging works by having a transmitter and receiver tuned to each other -- resonating at the same frequency -- to “maximize the energy transfer.” The Wireless Power Consortium chose not to tune the transmitter and receivers, an intentional effort to “maximize efficiency at short distances,” Perzow said. “It’s always been there, and we've always recognized the value” of resonant charging, something the WPC has been working on “for many years,” he said.

The technology has advanced to the point where WPC companies “demonstrated it at our last member meeting very successfully,” Perzow said. WPC showed a backward-compatible resonant system at CES and has achieved “significant technology milestones” in efficiency and interoperability, he said. The announcement about adding a resonant extension to the Qi spec was a “follow-up” to the CES demo, he said. He called out products from Convenient Power, a Hong Kong-based company that makes charging systems for cars, and from PowerbyProxi in New Zealand. In addition, he said, Philips, LG and others showed interoperability and “mature levels of design at our last members meeting,” and said resonance-based Qi products will be out before year end, likely before the spec is released.

Qi has been adopted successfully in the car environment in vehicles from Chrysler, Honda, Honda, Jeep, Toyota and Mercedes, he said. “They're in cars and they get it,” Perzow said of the carmakers. “By adding resonance, you can put [the transmitter] under the surface of a table or countertop, and the top of the table becomes your charging area,” he said. “You just put phone down on it."

The primary advantage of adding resonant technology is the ability to embed wireless charging capability into tables and furniture in a way that’s simple and somewhat seamless for consumers, Perzow noted. “When wireless charging is embedded into the environment -- into restaurants, tables, hotels, airplanes, trains, meeting rooms at work -- then a lot of things happen when you have a standard that allows that,” he said.

Instead of promoting wireless charging as a feature by itself, Perzow presented it as an enabler that allows consumers to use their smartphones to full potential. A business traveler in a hotel equipped with wireless charging places a phone on a charging-enabled bedside table “and pictures of your family, say, stream to a bedside digital screen,” he said. Or, a video on the phone might stream to the TV, and “through an app you've opted into, you might have access to room service, HVAC or lighting in the room,” Perzow said. A guest’s smartphone would become a “personal extension to the venue,” he said, made possible “only by plugging your phone in to keep it charged up,” he said, referring to wireless charging, which wouldn’t require that a phone be tethered to an outlet. ChargeSpot and Devant Technologies are two companies with embedded wireless charging solutions, he said.

Key to the advancement of the prototype version 1.2 Qi systems is compatibility with existing Qi 1.1 systems, and Perzow said a new Qi phone will work on an old Qi transmitter. The systems are interoperable and backward compatible within Qi, but to get the full benefit of charging at a 45mm distance (roughly 1.75 inches of separation), both devices need to be version 1.2-compatible, he said. An older model version 1.1 Qi phone working with a version 1.2 transmitter will work in resonant mode at 35mm, which Perzow called “sufficient to get into furniture efficiently.”

Another feature of the extension to the Qi spec is multiple-device charging using a single inverter, which Perzow called a simpler, less expensive solution to the current method. Previous Qi chargers that could charge multiple devices simultaneously had to do so using individual inverters for each device being charged, such as a smartphone or camera. The change to a single inverter design was made possible by a change to the communication protocol between the devices being charged and the transmitter, Perzow said. Multiple-device charging is another advantage that the A4WP claims with the Rezence wireless charging standard.