Modeling and Analysis of Multi-coil Magnetic Resonance Wireless Power Transfer Systems

Based on resonant inductive coupling, traditional wireless power transfer systems composed of transmitting and receiving coils could efficiently transfer energy only at short distances. The efficiency of the system decreases significantly with the increasing transmission distance. To maintain efficient power transfer at mid-range distance, a four-coil system with two self-resonant coils respectively close to the transmitting and receiving coils has been proposed by Andre Kurs. However, modeling and efficiency analysis of the system is based on coupled mode theory, which is obscure for electrical engineering researchers. In this paper, based on the lumped element circuit model, the efficiency, current gain and voltage gain calculations of multi-coil magnetic resonance wireless power transfer system are given. Considering operating frequency, coil resistance, mutual inductance and other parameters, the analysis of optimal conditions of efficiency can provide theoretical basis for further design and optimization of the system. Simulation results are presented to validate that a four-coil system can not only transmit power much more efficiently than a traditional two-coil system with the same transmission distance and coil size but also simultaneously adjust the current and voltage gain to meet the output power requirement of the system.