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Wireless Charging Plug-In Vehicles: Interoperability, Not First-To-Market, Determines Early Deployments

by Kevin Mak | Oct 25, 2016

On October 11th, 2016, Qualcomm announced that the refreshed 2017 Mercedes-Benz S-Class sedan plug-in hybrid, the S550e, will be offered with a wireless charging system based on its Halo design.

  • The model will feature a larger battery pack with a capacity of 13.3 kWh and enable a 50 km (31 mile) electric-only driving range.
  • The 3.6 kW (WPT 1, Wireless Power Transfer) system has a grid-to-battery efficiency of 90 percent, similar to existing conductive systems.   This enables a full recharge time of around 4 hours.

While this is the first announcement of a series production model offering wireless charging – this is not necessarily the first model to feature wireless charging as an as yet unannounced model could theoretically beat the Mercedes to market.

Furthermore, it is not necessarily in the best interest for most auto makers to be the first-to-market, as the key to wireless charging’s future success with plug-in vehicles is INTEROPERABILITY.

What usually happens in technology is that players try to beat their rivals to be first-to-market, to ensure the player’s prestige and be able to offer its systems as early as possible to sell more products.

  • This may be the case for certain luxury auto makers who want to enhance the user experience in owning a plug-in vehicle.
  • However, in the case of wireless charging in plug-in vehicles, the real competition would be CONDUCTIVE systems, not other players in the wireless charging sector.
  • At present, conductive systems are fraught with multiple standards.  There are the multitude of different regional plugs required for Levels 1 and 2 systems, as well as four different plugs for high power DC charging – CCS (Combined Charging System), ChaDeMo, the Chinese GB-20234 and the Tesla Supercharger proprietary system.
  • Conductive charging systems require consumers to get cables out of the vehicle and physically plug them to a charging point.  Wireless systems are both convenient and quicker to use, particularly for high power rates where conductive cables for 350 kW would require heavy cables with active cooling systems.
  • With the onset of autonomous vehicles, conductive charging would defeat the purpose because of the requirement for manned charging stations or would use complicated and less reliable robot arms to plug in cabling.
  • Dynamic charging, when the vehicle is simultaneously charged as it is driven, is only capable from wireless charging systems.  Such a concept can reduce the battery requirements for electric vehicles and so enable cost and weight reduction, with particular benefit for large vehicles, such as buses and trucks. 

The key enabler for wireless charging is to ensure interoperability between different design architectures (from Qualcomm, WiTricity, etc.), different OEMs and the public infrastructure. 

  • Should a consumer install a base charging pad at home for the Mercedes S550e, this consumer should not have to replace this charging pad should the vehicle be replaced for, say, a future BMW i8 or a Toyota Prius Prime. 
  • Neither should consumers be frustrated that the receiving pad on their Mercedes S550e cannot receive charge from a charging pad in a shopping mall parking lot.  They will want to know that it is compatible with a wide range of infrastructure.

So for the last few months, the SAE has been conducting interoperability bench testing at the Idaho National Laboratory with WPT 1 systems from Toyota and WPT 2 systems from Qualcomm (submission also supported by Daimler and Jaguar-Land Rover) and Nissan/WiTricity.

  • The process for standardisation has been for developers (Qualcomm, WiTricity) to generate the design architectures for licensed Tier 1 vendors (such as Delphi, Lear) to implement on each model for the OEM customer.  The standards body, such as SAE (Society of Automotive Engineers), brings in different design architectures and suggests certain specifications (such as communication systems and magnetic coil designs in the pads) to ensure interoperability between them.  It can list acceptable options, so long as they do not affect interoperability.
  • While a TIR (Technical Information Report) for the SAE J2954 standard was already published in May 2016 and that a Recommended Practice document is about to be released in early 2017, OEMs are not necessarily using these documents in a rush to offer wireless charging until later in 2018 when standards are finalised and when the vast majority of deployments will begin.
  • As members of the SAE, OEMs will decide on the reference designs from which they will have to comply with.  The standards aim to provide the OEMs with both the flexibility that will meet their requirements for their vehicles and the simplicity that would limit cost and development time.  While OEMs are focusing their developments on vehicle-side systems, they will need to comply with the standardised charging pad when deployments begin in public infrastructures.
  • For early deployments like the Mercedes S550e, the danger that interoperability might not be backward compatible with the final standards, but this would only affect a small number of vehicles, probably numbering less than 10,000 units that are also equipped with combustion engine-drive and conductive charging systems anyway.  






May: Technical Information Report J2954 (normative specification for both charging and receiving pad coils for WPT 1 (3.7 kW) and informative specification for WPT 2 (7.7 kW)),
Nov (later into 2017): Interoperability Test Results for WPT 1 and WPT 2, submissions made for WPT 3 (11 kW)

Early (possibly-Jan): Recommended Practice SAE J2954 for WPT 1 and WPT 2,
First wireless charging deployments

Final Standard J2954 and ISO 19363,
Recommended Practice SAE J2954 for WPT 3

Final Standard
for WPT 3

Exhibit 1 - Recent SAE Bench Testing at the Idaho National Laboratory

                                                                                                           Source: SAE

The key moment for wireless charging is when the 11 kW WPT 3 standard is finalised in the 2019-2020 timeframe – exactly when the next generation pure electric cars will enter the market with battery capacities that enable them to have a similar driving range as conventional vehicles.  11 kW is also the maximum charge level capable from residential electrical supply.  Until the arrival of new battery technologies that can enable frequent high power charging without damaging cell structures, high power DC charging will continue for fleets and rare passenger journeys along long distance highways.

Recent Strategy Analytics reports on wireless charging:

As a result, it is expected that all early-adopting models will not be launching their wireless charging offerings earlier than 2017, like the Mercedes S550e.  Beyond early adopting luxury auto brands, the majority of wireless charging deployment will begin in 2018 when standards are finalised.

(Later amended following additional insight from an industry player)
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