Wireless Battery Charger With Flexible Gains For Constant Current Or Constant Voltage Output

Inductive power transfer(IPT)technologies can deliver the energy in a predefined distance via the alternating electromagnetic field without the direct physical and electrical contact.IPT has been widely adopted in many fileds,such as consumer electronics,medical elecronics,electrical vehicle and rail transportation for the advantages of safety,convenience and friendly operation in harsh environments etc.In the portable device and electrical vehicle applications,the battery is an indispensable component which is used to store and supply the power.Lithium-ion batteries are identified as the most competitive candidate due to their high power density,long cycle life,and better safety.To realize the efficient charging and provide the sufficient protection for lithium-ion batteries,a load-independent constant current/constant voltage(CC/CV)output for the IPT battery charger is required to resist inevitable load variations and save additional DC/DC regulators.The loosely coupled transformer is a crucial component in an IPT system.To improve power transfer capability and transfer efficiency,compensation tanks are introduced in IPT topologies.The equivalent resistance of the battery varies in a wide range.Thus,an effective IPT converter must satisfy the following requirements: 1.The first CC and subsequcent CV output should be provided as battery required.2.CC and CV ouptus should combat the constraints of IPT transformer and the design of transformer can be readily optimized.3.Zero reactive power should be achieved to reduce the component ratings and improve the transfer efficiency.4.The additional cascading converters and hybrid topologies are avoided to save the cost,bulky and improve the system effiency and reliability.To achieve above goals,a general IPT model is introduced and analyzed to find out the matrix characteristic based on a two-port network.Lower order compensation topologies,such as four basic topologies SS,SP,PS,PP and three-conponent compensation topologies LC/S,S/LC,LC/P,P/LC,are well analyzed suitable for IPT battery.It is shown that LC/S,S/LC,LC/P,P/LC can realize CC and CV at two differrent resonatce frequencies.However,the CC and CV outputs rely greatly on the transformer parameters,so that it is hard to optimize the transformer if it is contrained in a given space.In this paper,some higher order compensation topologies are explored to achieve the adjustable output current and output voltage.The LC/LC compensation topology is investigated with the limited regulation on CC or CV.Thus LC/LC can be applied in the current-driven devices.To extend the CC range,a complementary LC/CC topology is further proposed,and the prototype of the IPT converter with three different current 0.28 A,0.46 A,1.28 A and the single IPT transformer is build to verify the above analysis well.To have flexble CC and CV output suitable for IPT battery chargiers,,a six-component compensation topology LCC/LCC is given to realize the required load-independent CC and CV outputs at two zero-phase angle(ZPA)frequencies,which can also combat the constaints of transformer parameters.The sensitivities of compensation parameters to the input impedance and load-independent output are discussed.Finally,an IPT battery charger prototype with 1 A charging current and 24 V battery voltage is built to verify the theoregical analysis.