Range and misalignment tolerance comparisons between two-coil and four-coil wireless power transfer systems

Two-coil and four-coil magnetic resonance coupled wireless power transfer (MRC-WPT) system configurations are analyzed and compared in this paper based on the simplified circuit model and 3-D physical model simulations. Physical model simulation results of symmetrical MRC-WPT systems show that when the sizes of transmitter (Tx) coil and receiver (Rx) coil are equal and without any external capacitors, the four-coil system achieves longer transmission distance and larger misalignment tolerance with relatively lower efficiency at close distance compared to the two-coil system. The designed 10-turn, 400mm outer diameter spiral shape four-coil WPT system achieves operation distance of 500mm with nearly constant maximum transmission efficiency of 85%, while the two-coil system achieves ∼96% of efficiency up to distance of 350mm. When the vertical Tx to Rx distance is fixed at 150mm, the four-coil system has a larger lateral misalignment tolerance of 275mm compared to the two-coil system which has misalignment tolerance of 200mm at the same distance.