This paper deals with a wireless power transfer system where a novel structure of transmitting/receiving double DD coils is applied. This system uses two identical double D (DD) transmitter coils stacked on each other to transfer power to two stacked receiver coils. The power is transmitted simultaneously and independently through both transmitter coils to the receiving coils. The magnetic field of the first coil does not interfere with the second coil. Both transmitter and receiver coils are placed on each other and occupy the same footprint, so there is no need for increased space. This can lead to an interesting wireless power transfer system—from single load to double the load and higher power transfer density.

This paper presents the evolution of an inductive wireless power transfer using a multicoil system. The double DD coil structure on the transmitter and the receiver side using two perpendicular bipolar DD coils is upgraded with an additional nonpolar quadrature coil. The proposed structure can be called the double DDQ coil structure. All three coils are not coupled, due to the nature of the directional double DD coil. If the transmitter and the receiver are not misaligned to one another, the system behaves as three separate, uncoupled IPT systems. The main advantage of the proposed coil topology is additionally increased power density and increased misalignment tolerance. Additionally, when the transmitter and the receiver coil are perfectly aligned, the proposed pad structure can transmit three different voltages and can be excited with different frequencies. In the case of this paper, the three coils on the transmitter side were excited by the same frequency. The proposed coil was evaluated experimentally and compared to the system using double DD coil structure.

Circular planar spiral coils are the most important parts of wireless power transfer systems. This paper presents the optimization of wireless power transfer coils used for wireless power transfer, which is a problem when designing wireless power transfer systems. A single transmitter coil transfers power to a single receiving side. The performance of the wireless power transfer system depends greatly on the size and shape of the wireless power transfer system. Therefore, the optimization of the coils is of the utmost importance. The main optimization parameter was the coupling coefficient between the transmitter and the receiver coil in the horizontally aligned and misaligned position. A genetic evolutionary algorithm was used to optimize the coil, according to the developed cost function. The algorithm was implemented using the MATLAB programming language. The constraints regarding the design of the coils are also presented for the problem to be analyzed correctly. The results obtained using the genetic algorithm were first verified using FEM simulations. The optimized coils were later fabricated and measured to confirm the theory.

This paper describes the control of a wireless power transfer system using a double DD coil structure, when the transmitter and the receiver coil are rotated to one another. WPT systems using single DD coils are rotationally dependent, due to the directional magnetic field generated by the DD transmitter coil. This rotational dependance can be mitigated by using a different transmitter structure. One such possibility is the usage of the double DD coil on the transmitter and the receiver sides. A double DD coil includes two directional DD coils, which can be excited separately. The coils inside the coil structure are perpendicular to one another, which allows higher power density and additional rotation tolerance. The proposed system was tested on a low power laboratory experimental setup.

When designing a wireless power transfer system, overall system efficiency is one of the key parameters. The efficiency depends on several parameters, which also includes control modulation, used for excitation of the transmitter coil. However, how much the modulation technique impacts the efficiency is studied rarely. In this paper, we compare the three most popular control modulation techniques for transmitter voltage of a wireless power transfer system. First, the theory behind the methods is presented by highlighting the difference between them and their implementation. The methods are implemented, together with a linear PI control scheme, to evaluate the efficiency and performance of each of the methods. Finally, the practical tests were performed, under different output power levels, in order to evaluate the practical performance of each modulation strategy further.

This paper proposes an on-line method for foreign object detection in a double DD coil system. The foreign object is detected by real-time measurement of the mutual inductance between the transfer pads. Measurement of the mutual inductance between coils can be performed at the start, during initialisation, or during the wireless power transfer. The coils in the double DD coil structure can be used separately; one coil can be used for power transfer and the other can be used for the mutual inductance measurement. The mutual inductance measurement is based on the voltage measurement across the open circuit receiver coil. The measured value of mutual inductance between the transmitter and the receiver pad can be used in a control algorithm and in a foreign object detection algorithm. Additionally, a 2DDq coil structure can be used as a replacement for the double DD coil structure, which increases the power transfer density. The DD coils in the double DD coil structure can also be driven using two phase-shifted voltages, which enables better location and detection of foreign objects. The method also helps to differentiate the mutual inductance change due to the distance change from the mutual inductance change due to the presence of a foreign object.