Research On Implantable Wireless Power Transfer System With Constant Output Voltage Or Constant Output Current

Using wireless power transfer technique to power implantable medical devices has the advantages of safety,flexibility and high reliability.When the relative position of the transmitting coil and the receiving coil,the working state of the device or the charging state of the implantable lithium battery changes,the output voltage or current of the implantable wireless power transfer system will fluctuate.These situations affect the constant voltage for powering implantable devices or constant current for charging of the lithium battery.At the same time,the topology design of implantable wireless power transmission system is facing challenges due to the limited volume of the implants.Therefore,this paper will study wireless power transfer system with consant output voltage or constant output current from the point of view of resonant compensation networks.Following work is carried out:Firstly,the structure and equivent circuit of implantable wireless power transfer system are introduced.The output characteristics of SS,SP,PP,PS compensation networks are derived and their shortcomings are pointed out.The output characteristics of two kinds of high-order compensation topologies,i.e.T-type compensation network and π-type compensation network,are further analyzed,which lays a foundation for the study of resonant topologies suitable for implantable wireless power transfer system with constant output voltage or constant output current.Secondly,seven compensation networks to achieve constant output voltage of WPT system is construced by adopting T-type resonant compensation network on both transmitting and receiving sides.Comparing transfer characteristics of WPT system and numbers of compensation components,the LCC-PS wireless transfer system is determined as the best compensation networks with constant output voltage.To realize constant output voltage when mutual inductance changes,output voltage identification method on the transmitting side of LCC-PS WPT system is proposed.PSIM simulation is carried out and the results shows that the system has good characteristics of constant output voltage,and the proposed output voltage identification method can accurately detect the system output voltage.Then,seven compensation networks to achieve constant output voltage of WPT system is construced by adopting T-type resonant compensation network on the transmitting side and π-type network on the receiving sides.Comparing transfer characteristics of WPT system and numbers of compensation components,the LCC-SP wireless transfer system is determined as the best compensation networks with constant output currnet.To realize constant output current when mutual inductance changes,output current identification method on the transmitting side of LCC-SP WPT system is proposed.PSIM simulation is carried out and the results shows that the system has good characteristics of constant output current,and the proposed output voltage identification method can accurately detect the system output current.Finally,a propotype of wireless power transfer system for spinal cord stimulator is built to verified the accuracy of implantable wireless power transfer system.