**1. Introduction**

In recent years, studies on DWPT have gained traction especially from The University of Auckland, Korea Advanced Institute of Science and Technology (KAIST), The University of Tokyo,OakRidge NationalLaboratory (ORNL), and many otherinternational institutions.The topics discussed include system modeling, control theories, converter topologies, magnetic coupling optimization, and electromagnetic shielding technologies for DWPT.

The University of Auckland and Conductix‐Wampfler manufactured the world's first WPT bus with 30 kW power. A demo ET with 100 kW WPT capability and a 400 m long track without any on‐board battery was also constructed [1] as shown in **Figure 1**.

**Figure 1.** WPT for EV and ET.

KAIST constructed electric buses powered by an online electric vehicle (OLEV) system. The buses are deployed in Gumi city for public transportation, running on two fixed routes covering a total distance of 24 km as shown in **Figure 2**. The OLEV system on these routes is able to supply 100 kW power with 85% of transfer efficiency [2].

**Figure 2.** KAIST OLEV.

The research in Oak Ridge National Laboratory focuses on coupling configuration, transfer characteristics, medium loss, and magnetic shielding. The dynamic charging system as shown in **Figure 3** constructed by ORNL consists of a full bridge inverter powering two transmitters simultaneously through a series connection. The experimental results show that the positions of the electric vehicle significantly affect the transferred power and efficiency [3].

**Figure 3.** DWPT system of ORNL.

**1. Introduction**

110 Wireless Power Transfer - Fundamentals and Technologies

**Figure 1.** WPT for EV and ET.

**Figure 2.** KAIST OLEV.

In recent years, studies on DWPT have gained traction especially from The University of Auckland, Korea Advanced Institute of Science and Technology (KAIST), The University of Tokyo,OakRidge NationalLaboratory (ORNL), and many otherinternational institutions.The topics discussed include system modeling, control theories, converter topologies, magnetic

The University of Auckland and Conductix‐Wampfler manufactured the world's first WPT bus with 30 kW power. A demo ET with 100 kW WPT capability and a 400 m long track without

KAIST constructed electric buses powered by an online electric vehicle (OLEV) system. The buses are deployed in Gumi city for public transportation, running on two fixed routes covering a total distance of 24 km as shown in **Figure 2**. The OLEV system on these routes is

The research in Oak Ridge National Laboratory focuses on coupling configuration, transfer characteristics, medium loss, and magnetic shielding. The dynamic charging system as shown in **Figure 3** constructed by ORNL consists of a full bridge inverter powering two transmitters simultaneously through a series connection. The experimental results show that the positions

of the electric vehicle significantly affect the transferred power and efficiency [3].

coupling optimization, and electromagnetic shielding technologies for DWPT.

any on‐board battery was also constructed [1] as shown in **Figure 1**.

able to supply 100 kW power with 85% of transfer efficiency [2].

Researchers in The University of Tokyo proposed using the combination of a feedforward controller and a feedback controller to adjust the duty cycle of the power converters in the DWPT system to achieve optimum efficiency. With the advanced control method, a wireless in‐wheel motor is developed as shown in **Figure 4**. The current WPT is from the car body to the in‐wheel motor. In future, the wireless in‐wheel motor can be powered directly from the ground using a dynamic charging system [4].

**Figure 4.** Wireless in‐wheel motor.

On the other hand, the Korea Railroad Corporation (KRRI) designed a WPT system for the implementation in railway track. A 1 MW, 128‐m‐long railway track was developed to demonstrate the dynamic charging technology for EV. The coupling mechanism consists of a long transmitter track and two small U‐shaped magnetic ferrites to increase the coupling strength. As a long transmitter track has high inductance, high voltage drop will occur when the current flows through it. In order to reduce this voltage stress, the compensation capacitors are distributed along the track as shown in **Figure 5** [5].

**Figure 5.** Wireless power rail developed by KRRI.

The researchers from the Japan Railway Technical Research Institute proposed a different design of coupling mechanism for the ET. The transmitters are long bipolar coils, and "figure‐ 8" coils are used as the matching pickups as shown in **Figure 6**. The system is able to transfer 50 kW of power across a 7.5‐mm gap with 10‐kHz frequency [6].

**Figure 6.** The non‐contact power supply system for railway vehicle.

Bombardier Primove from Germany is currently leading in WPT technology for EV and ET. Studies have been primarily conducted for better exploitation of the technology. Apparently, the technical information of the WPT system developed by Bombardier Primove has not been published. In 2013, the company proposed a design shown in **Figure 7** to ensure high reliability when powering the EV. The main DC bus is supplied by k‐number of AC/DC substations connected in parallel. This configuration is used to increase the robustness of the system. If one of the AC/DC substations breaks down, that particular substation will be disconnected from the system and other neighboring substations can continue functioning normally, thus avoiding power interruption. Each transmitter cluster is supplied by multiple high‐frequency DC/AC inverters in parallel. Similar to the DC bus, the power supply at the AC bus will not be interrupted if an inverter breaks down. At the receiver side, the train contains a DC bus as shown in **Figure 7**. Multiple receivers are supplying to the DC bus simultaneously via AC/DC rectification. The DC bus powers the motor through a controller. If any of the rectifiers is damaged, other receivers can continue providing sufficient power to the DC bus [7].

**Figure 7.** DWPT system for railway vehicle.

The Harbin Institute of Technology demonstrated dynamic charging using segmented transmitters with parallel connections to the inverter [8]. At the receiver side, two layers of flat coils wounded in the same direction are stacked against each other to cancel the points, where transferred power is zero, thereby increasing the overall efficiency. Using the decoupling principle to design the size and position of the two‐phase coil, the cross‐coupling is cancelled and high efficiency is then achieved at any position [9].

Although several studies have been conducted all over the world yielding exceptional results, factors such as power transfer performance, construction cost, and maintenance cost still require improvement. Other important considerations for practical DWPT implementation include high‐power rail, robust control strategies, and EMC.
