Research On Non-radiative Wireless Electromagnetic Power Transfer

With the development of science and technology,wireless communication technologies have been widely employed in many applications,such as wireless sensor networks,wireless medical robots,and robots working in strong radiation environment.The harsh environment limites the direct electrical power supply with wired transmission methods.The wireless power transfer technologies which can provide energy supplies in these applications is needed.Among various wireless power transfer technologies,the inductive power transfer technology(IPT),which transfers power through alternating magnetic fields,has many advantages,such as a large power capacity,negative effection of dielectric obstacles,strong environmental adaptability and flexible access modes,which make IPT attractive recently.Its application prospects include electronic devices charging without perception,energy supply for medical implantable devices,static and dynamic charging of electric vehicles,and contactless power supply for various special complex occasions.However,the effective power transfer distances of traditional IPT are relatively short.Therefore,one of the research hotspots on IPT is to improve its transfer performance,that is,to improve the wireless power transfer efficiency under a certain transfer distance or to improve the transfer distance under the premise of ensuring a certain transfer efficiency.There are three main methods to improve the performance of IPT system:(1)increasing the operating frequency of the system;(2)increasing the mutual inductance between the transmitting coil and the receiving coil;(3)reducing the losses in the coils and their peripheral compensation circuits.However,due to the respective limitations of the three methods,the system performance cannot be further improved.In this dissertation,firstly,a novel type of coil,named alternative-winding coil,with a working frequency higher than the self-resonant frequency is proposed based on the study of the current distribution of the coil along the wire at different excitation frequencies.The new power transfer system works well without additional compensation circuit,which eliminates the heat loss caused by the compensation circuits.Secondly,the equivalent circuit of the alternative-winding coil has been imposed and been used to analyze the power transfer efficiency,input impedance and optimal load impedance,etc.Thirdly,the factors that which may deteriorate the transfer efficiency of the IPT system constructed with AWC are analyzed,which can guide the coil design in wireless power transfer systems.Finally,alternative-winding coils are fabricated and tested.The experimental results are in good agreement with the theoretical analysis.As an attempt,this dissertation proposes a structure which can bind electromagnetic energy and make it perform a swirling motion.Unlike the traditional orbital angular momentum wave,the Poynting vector of the swirling motion electromagnetic wave is circumferential.Then,a wireless power transfer experiment employing swirling motion electromagnetic wave is carried out.The experimental results show that:(1)When the receiving device is inside the swirling motion electromagnetic field,the system can obtain relatively stable power transfer efficiency;(2)The swirling motion electromagnetic field bind most of the electromagnetic energy inside the structure without radiating outward.Accordingly,the swirling motion electromagnetic wave is potential in the field of wireless power transfer.