Wireless charging in Japan: Sanyo Electric's contactless charging pad

No matter where and when, you can charge it by just placing it on the ground... To realize this concept, research and development activities related to wireless power supply for portable terminals are becoming increasingly active.

16 products supporting the standard were exhibited at the WPC conference.

Leading these R&D activities is the Wireless Power Consortium (WPC), an industry group for wireless power supply. The group was established in December 2008 with the goal of industry standardization of wireless power supply methods. Currently, relevant specifications have been formulated, and relevant manufacturers are steadily advancing the development of supporting equipment Note 1).

Note 1) In July 2010, WPC completed the development of transmission standards for portable products with output power below 5W, such as smartphones and digital cameras.

Sanyo Electric, which has been actively participating in WPC activities, is one of the founding companies of WPC and the only "Regular Member" in Japan that can participate in the formulation of standard specifications. Although Sanyo Electric has always been very low-key, in December 2010, Sanyo Electric announced its product supply plan, etc. At the same time, it also released prototypes such as charging stations for portable terminals that support WPC specifications and battery packs with non-contact charging functions for mobile phones.

SANYO Electric demonstrated its idea of ​​actively developing related businesses: "In 2011, we will begin to work on popularizing contactless charging technology. This technology will definitely become part of social infrastructure in the future. By 2015, the concept of charging portable products may change dramatically" (Masakazu Toya, business manager of the charging system business department of SANYO Electric Mobile Energy Company).

To achieve position freedom first

Sanyo Electric wants to achieve two goals in WPC. The first is interoperability. That is, as long as it complies with the WPC standard, charging equipment from different manufacturers can be used interchangeably. To this end, devices that comply with the WPC specification are marked with the "Qi" mark.

To ensure this interoperability, WPC has roughly classified the charging board methods into three types (Figure 1). This is to reduce the workload of the working status confirmation test. On the other hand, it can allow a certain degree of freedom in the design of the power receiving device.

Figure 1: There are three types of charging plates. The WPC specification stipulates three types of charging plates:
the "coil array type" in which portable products can be charged by placing them anywhere on the charging plate, the "movable coil type" and the "magnetic attraction type" in which portable products can be charged by placing them in a designated place using a guidance function.

Another goal is to achieve a high degree of freedom in position. SANYO Electric's position is "charging at any position is the top priority" (SANYO Electric Yuan Ya). This was also an absolute condition for SANYO Electric to participate in WPC when WPC was established in December 2008 and it was uncompromising.

The background is that WPC uses electromagnetic induction wireless power supply technology. Although this method is an "old technology" and its principle has been confirmed, there is still a problem that the power transmission efficiency will be greatly reduced if the positions of the power transmission and receiving coils do not match.

Therefore, Sanyo Electric designed a "movable coil type" solution that integrates a stepping motor inside the charging plate to move the power transmission coil.

Motor used in CD players

Sanyo Electric has made improvements to ensure that power can be transmitted efficiently regardless of the position of the portable terminal placed on the charging plate. Specifically, a dedicated coil for estimating the position of the portable terminal is set up, which is different from the coil for power transmission (Figure 2). The current is passed through the position estimation coils arranged in a matrix, and the state changes caused by the placement of the portable product are detected to determine the position of the power transmission coil. The power transmission coil is then moved to the bottom of the portable product. Toya said that the current flowing through the position estimation coil is very small and "has almost no effect on power consumption."

Figure 2: SANYO Electric has prepared products for both the power transmission and reception ends
The charging plate developed by SANYO Electric is a movable coil type, equipped with a dedicated coil to accurately infer the position of the portable terminal (a). The shape and position of the coil are all guessed by this site. The battery pack that supports the WPC standard adopts the same shape as the existing battery pack (b).

Although this measure will lead to an increase in costs, the company has found a corresponding solution. For example, the stepping motor, which is the key to the movable structure, is used in the portable CD player. In addition to reducing component costs by using general-purpose products, their proven durability and high reliability also promoted their adoption.

While developing the charging plate, Sanyo Electric is also promoting the development of the power receiving end. Specifically, it is to equip portable products with a dedicated battery pack to support wireless power supply. In the battery pack, which is the same size and shape as the existing battery pack, in addition to the rechargeable battery, it also contains a coil for receiving power, a magnetic sheet for suppressing noise, and a control circuit board (Figure 3). According to Sanyo Electric, in order to equip the largest lithium-ion rechargeable battery possible, efforts are being made to further miniaturize and thin the magnetic sheet and the coil for receiving power.

Figure 3: Small battery capacity, PET sheet removed
The figure shows the internal structure of a battery pack developed by Sanyo Electric that supports contactless charging. Because it not only has a built-in power receiving coil, but also a built-in control circuit substrate and magnetic sheet, the capacity of the lithium-ion rechargeable battery is about 10% smaller than that of a normal battery pack. (Figure based on Sanyo Electric's data)