SMFIR allows for charging in motion

With a constant demand for cleaner energy sources as technology advances, one alternative that has been receiving a lot of attention in recent years is electric cars. It has been a goal among many researchers to cut the cost of batteries in electric cars so that the vehicles can become a competitive alternative to the traditional engine-operated cars.

In 2010, researchers at the Korea Advanced Institute of Science and Technology (KAIST) developed a wireless charging technology called Shaped Magnetic Field in Resonance (SMFIR). This new method of charging is compatible with online electric vehicles (OLEVs) and could allow electric cars to collect electricity from a road-embedded charging system, making electric cars a much more viable form of transportation.

In his 2011 paper titled “Application of SMFIR Technology to Future Urban Transportation,” professor of the Graduate School for Green Transportation at KAIST In-Soo Suh states that “SMFIR technology enables the electric vehicle to be charged while the vehicle is in motion” as opposed to being charged from traditional charging stations. Power cables embedded in the road create magnetic fluxes, which can be collected by OLEVs to fuel them.

The charging mechanism on the road gets activated only when OLEVs run over it, so other vehicles will not be hindered by the magnetic field. When an OLEV hovers over the charging mechanism, a power inverter installed on the road lets current flow. Then the pickup device — made of a ferrite core and coiled with copper wires — installed underneath the vehicle collects the magnetic flux. After the induced current of collected magnetic flux is converted into DC power, the Power Distribution Unit (PDU) then distributes it to the appropriate sectors within the vehicle.

The harvested electricity can be either used to operate the electric motor or can be stored in a battery for emergency purposes. This battery is one-third to one-fifth the size of the battery for traditional electric vehicles because OLEV does not require as much storage space. Also, vehicles can be charged either when they are running or when they are stationary. According to KAIST, only 5 to 15 percent of the road needs to have charging devices implanted in order for the vehicles to safely operate.

Suh’s paper further explains the processes of wireless power transfer systems: the supply mechanism embedded on the road operates by having multiple segments of powered cable loops with various lengths. Each segment has two cable lines with currents of opposite directions, which creates a dense magnetic flux in between the cables.

When the sensor on the road detects an OLEV, the powered cable loops begin the supply process. The ferrite structure within the segment determines the shape of the magnetic field, which influences the density of the magnetic flux.

Thus, depending on the vehicle profile — such as its speed and acceleration — on certain parts of the road, design decisions of the supply mechanism (such as where to install it or how long the segment should be) can be altered for the optimum efficiency.

Currently, OLEVs are being tested in many regions of Korea. Since March 2010, OLEV trams in Seoul Grand Park in South Korea have been used to transport visitors to various destinations around the park. Also, since last July, OLEV buses have been tested as a public transportation system for Gumi-Si in Korea. OLEVs are an optimal fit for public transportation systems like buses and trains, as those vehicles operate on predetermined tracks, allowing for easier and more efficient installation of power cables.