Research On Hybrid Battery Wireless Charging System And Efficiency Enhancement In Wide Load Range

Inductive power transfer(IPT)is a novel technique using the alternating electromagnetic field to deliver energy from power supply to loads without physical contact.Due to its convenience,reliability and safety,IPT has been widely employed in a lot of wireless charging applications,e.g.,mobile devices,biomedical implants,electric vehicles(EVs),and so on,ranging from the low power to the high power.Lithium-ion batteries and supercapacitors are widely used in the above charging occasions due to their advantages such as high energy density and large charging cycles,and their charging process mainly include two modes: constant current(CC)mode and constant voltage(CV)mode.Characteristics of such IPT charger greatly rely on parameters of the key loosely coupled transformer.For fixed-size IPT transformers,the IPT charger is difficult to provide the desired CC and CV output directly.In addition,the equivalent resistance of the battery varies in a wide range during the entire charging process.It is difficult to maintain high efficiency within a wide load range.Therefore,an IPT converter is expected to realize the required CC and CV output in a wide load range efficiently.To combate the constraints of loosely coupled transformer parameters,this paper proposes a systematical method to derive effective hybrid IPT converters,while maintaining nearly unity power factor and soft switching of power switches simultaneously.Starting from some existing topologies having the configurable CC or CV output,the IPT converter cascades a general T or PI network for mode transition.Design principles with fewer mode switches and compensation components are proposed.Some available hybrid topologies are then given in this paper regardless of the constraints of LCT parameters.Control logic,sensitivities of compensation parameters to the input impedance and the load-independent output are also discussed.Finally,a 1 k W prototype of hybrid IPT battery charger based on LCC-LCC and LCC-S topologies is built to verify the theoretical analysis.Compared with Lithium-ion batteries,supercapacitors have a much wider range of load variation during the CC charging process,which makes constant current charging and efficiency enhancement challenging to the IPT converter design.To solve it,this paper identifies load transformation ability of a current-controlled semi-active rectifier(CCSAR)to comply with the required load matching for efficiency enhancement throughout the CC charging process of the supercapacitor.Takeing SP-compensated IPT converter as an example,this paper designs a 100 W single-stage IPT converter based on the CCSAR,and an effective control strategy is also proposed.A desired CC output as well as the efficiency enhancement can be implemented by using a bivariate modulation,which includes the modulation of the inverter operating frequency and the CCSAR conduction angle.Finally,experiment results validate the CC output and the enhanced efficiency well.