Analysis of forces on the coupler of a wireless power transfer system under typical faults

Typical faults in wireless power transfer systems, such as grounding and disconnection issues, can cause significant current surges and electromagnetic force increases, necessitating consideration of the magnetic shielding structure’s force distribution to maintain stability, with the system stabilizing after about forty fault cycles and the multi-slot structure’s design affecting the electromagnetic stress distribution.

• Typical faults in wireless power transfer systems include grounding and disconnection of the transmitter busbar, damage to the transmitter inverter bridge, grounding of the receiver busbar and open circuit of the load, and damage to the receiver rectifier bridge. By summarizing the characteristics of faults, the faults in wireless power transfer systems can be regarded as any periodic combination of open circuit and short circuit on the transmitter side and open circuit and short circuit on the receiver side.
• Under the open circuit fault on the receiver side of the wireless power transfer system, a large current surge will be generated inside the Litz wire coil. The high-frequency electromagnetic force acting on the coupling mechanism increases sharply. To ensure the stable operation of the wireless power transfer system, it is necessary to consider the distribution of electromagnetic forces in the magnetic shielding structure under fault conditions, that is, the open circuit on the receiver side.
• After the open circuit fault occurs on the receiver side coil of the wireless power transfer system, the amplitude of the current flowing through the transmitter coil oscillates sharply, causing the amplitude of the spatial electromagnetic field strength between the coupling mechanisms to increase sharply. The electromagnetic force acting on the magnetic shielding layer of the wireless power transfer system on both sides will also oscillate sharply. The steady-state Kelvin force acting on the magnetic shielding layer formed by the stacking of the magnetic shielding layer is approximately the square of the amplification multiple of the current flowing through the coil. After about forty damaged fault cycles, the electromagnetic force acting on the coupling mechanism of the wireless power transfer system returns to a stable state.
• Considering the characteristics of the multi-slot structure, the edge slot side wall of the magnetic shielding layer will converge the spatial magnetic field lines, resulting in a stronger surface electromagnetic stress on the edge slot side wall. At the same time, the aggregation effect of the sharp part on the spatial magnetic field lines causes a stronger surface electromagnetic stress distribution on the sharp part. It should be noted that the vibration frequency caused by the electromagnetic force on the coupling mechanism of the wireless power transfer system is twice the resonant frequency of the wireless power transfer system. After the open circuit fault occurs on the receiver side coil of the wireless power transfer system, the electromagnetic force acting on the transmitter coil and the magnetic shielding layer is consistent, and at the same time, since the current flowing through the receiver coil is zero, the receiver coil will not be affected by the high-frequency electromagnetic field force between the coupling mechanisms.