A Linear Extendable Phase-shift Controlled Multi-coil Transmitter Architecture for Wireless Power Transfer with 3D Magnetic Field Shaping

Wireless power transmission (WPT) systems operating at MHz have advantages of small size and a high tolerance for coils misalignment. There is an urgent need for existing MHz WPT systems to improve coupling coils efficiency and positional freedom of the receiver simultaneously. There exist some ways for improving coils efficiency and positional freedom of the receiver, such as introducing repeater coils and employing special coils structures. However, lack of magnetic field strength can limit the freedom of the receiver, and the excessive coupling may cause inefficiency in coils. This paper proposes a phase-shift controlled multi-coil transmitter architecture. The architecture is linear extendable and it enables the 3D magnetic field shaping, which helps to improve the coupling coils efficiency and the spatial freedom of the receiver. The design of the compensation capacitors of the transmitting coils is discussed to achieve the optimal operation for the high-frequency power amplifier (PA) when considering the effect of the cross-coupling among transmitting coils. The mathematic model for the 3D magnetic field shaping is derived to prove the concept of the approach. The calculation results show the capability of 3D magnetic field shaping when using a two-coil transmitter as an example. The experimental results match well with the theoretical analysis and the simulation results. Three WPT systems are studied in the paper. Compared with the single transmitter system (STS) and the two-coil transmitter system (TTS) without phase-shift control (PSC), the TTS with PSC can maintain higher system efficiency in three degrees of freedom (vertical movement, horizontal movement, flip with fixed axis). In particular, only the TTS with PSC can work when the receiving coil is perpendicular to the transmitting coils. Therefore, due to the ability to shape the 3D magnetic field, the linear extendable multi-coil transmitter architecture with PSC has advantages in terms of the receiver freedom and the coupling coils efficiency.