Beom W. Gu

Advances in Wireless Power Transfer Systems for Roadway-Powered Electric Vehicles

Roadway-powered electric vehicles (RPEVs) are attractive candidates for future transportation because they do not rely on large and heavy batteries but directly and efficiently get power while moving along a road. The inductive power transfer systems (IPTSs) that have been widely used for the wireless powering of RPEVs are reviewed in this paper. The development history of the IPTS is tracked from the origin of the RPEV in the 1890s to the recent RPEV. Throughout its 100-year history, the size, weight, efficiency, air gap, lateral tolerance, electromagnetic force, and cost of the IPTS have been substantially improved, and now RPEVs are becoming more widely commercialized. Important milestones of the developments of the IPTS and RPEVs are summarized in this paper, focusing on recent developments of on-line electric vehicles that were first commercialized in 2013.

Generalized Active EMF Cancel Methods for Wireless Electric Vehicles

In the inductive power transfer systems (IPTSs) of wireless electric vehicles (WEV), the electromagnetic field (EMF) should be lowered for the safety of pedestrians. In general, the EMF should be canceled for every space, time, and load condition of interest. Three generalized design methods for cancelling the EMF of WEV are proposed in this paper. By adding active EMF cancel coils to each primary main coil and secondary main coil, respectively, the EMF generated from each main coil can be independently cancelled by their corresponding cancel coils. Moreover, the EMF can be successfully mitigated if a dominant EMF source only is cancelled with 3-dB margin, which can be applied to any resonant type wireless power transfer systems. Furthermore, no significant power drop may occur if the cancel coils are placed aside from magnetic coupling path. Design examples are shown for U-type and W-type IPTS as well as a wireless stationary EV charger. Experimental verifications are shown for a recently developed I-type IPTS, which has a narrow rail width structure with alternating magnetic polarity along with a roadway. The proposed design methods have been demonstrated, without the loss of generality, to only the secondary coil where relatively large EMF is generated due to high ampere turns. An optimum spacing for cancel coils from main coils and an optimum number of turns are determined. Through experiments, additional EMF mitigation techniques such as the magnetic mirror method, separating pick-up rectifiers, and passive Al plate are provided. Thus, the EMF at 1 m distance from the center of a pick-up becomes under 44 mG even for the maximum power of 12 kW.

Ultraslim S-Type Power Supply Rails for Roadway-Powered Electric Vehicles

An ultraslim S-type power supply rail, which has a width of only 4 cm, for roadway-powered electric vehicles (RPEVs) is proposed in this paper. The cross section of the core has a thin S-shape, and a vertically-wound multiturn coil is displaced inside the core. In this way, the most slim power supply rail is designed, which is crucial for the commercialization of RPEVs. The construction of roadway infrastructure, which is responsible for more than 80% of the total deployment cost for RPEVs, can be much easier when the width of the power supply rail is so small. To increase portability and to minimize construction time, a foldable power supply module is also proposed in which flexible power cables connect each foldable power supply module such that no connectors are needed during deployment. An effective winding method for minimizing the cable length is proposed, and an optimum core thickness of the proposed power supply rail is determined by FEA simulations and verified by a prototype power supply module. By virtue of the ultraslim shape, a large lateral displacement of 30 cm at an air gap of 20 cm was experimentally obtained, which is 6 cm larger than that of the I-type power supply rail. In addition to the larger lateral displacement, it is estimated that the S-type one has lower EMF than the I-type one because the width of the S-type one is narrower than that of I-type one. The maximum efficiency, excluding the inverter, was 91%, and the pick-up power was 22 kW.

Generalized Models on Self-Decoupled Dual Pick-up Coils for Large Lateral Tolerance

Self-decoupled dual pick-up coils for large lateral tolerance and low electromagnetic field for pedestrians are proposed. Analytical models are developed that are applicable to any self-decoupled coils, regardless the coil types such as single/dual pick-ups and core/coreless coils. An optimum decoupling distance between adjacent pick-up coils is determined and found to be independent of the existence of a core plate. Maximum load power over a large lateral tolerance is obtained for the optimum decoupling distance. The proposed models are so general that they can be applied to any self-decoupled pick-up coils for stationary charging and dynamic charging systems. Moreover, the self-decoupled coils are compatible with any compensation method such as serial, parallel, and serial-parallel. A prototype system of 1.5 kW and Q = 60 for roadway powered electrical vehicles was implemented and showed fairly good agreements with the theoretical models and simulations. The measured lateral tolerance was 90 cm, which is about 1.5 times of the coil width.

Tethered aerial robots using contactless power systems for extended mission time and range

Tethered aerial robots (TAR) that can be continuously powered by power cables for extended mission time and range are newly proposed. The TAR can overcome the limited mission time of conventional battery-based aerial vehicles and the mission range is quite extended with a virtue of a long aerial multi-wounded power cable. The TAR is equipped with an aerial contactless power system (ACPS) for avoiding the use of brush and an aerial tension control system (ATCS), first proposed in this paper, for avoiding tangled power cable. A prototype TAR including the ACPS and ATCS was developed and successfully demonstrated at outdoor environment, where the output power of 180 W at 100 kHz and a flight altitude of 20 m for 30 minutes were achieved.

Trends of Wireless Power Transfer Systems for Roadway Powered Electric Vehicles

Roadway powered electric vehicles (RPEV) are attractive candidates for future transportations because they are free from large and heavy batteries but directly get power efficiently while moving along a road. The inductive power transfer systems (IPTS) that have been widely used for the wireless powering of RPEV are reviewed in this paper. Main milestones of the developments of the IPTS and RPEV are summarized in this paper, mainly about the recent developments of on-line electric vehicles (OLEV) that have been commercialized first in 2013.

Self-decoupled dual pick-up coils with large lateral tolerance for roadway powered electric vehicles

Self-decoupled dual pick-up coils for roadway powered electric vehicle (RPEV) with large lateral tolerance and low EMF for pedestrians are proposed. The accurate equivalent circuits and mathematical models for the dual pick-up coils are completely developed to decouple the two adjacent pick-up coils for the both cases with and without core plates. The proposed models are verified by simulations and experiments. It is found that the adjacent pick-up coils can be decoupled regardless of the existence of core plates by overlapping the pick-up coils and the overlapping is nearly same for the both cases with and without core plates.