Research On Novel Topologies And Structures Of Capacitive Power Transfer System

Capacitive power transfer(CPT)utilizes high frequency electric field to transfer energy from the transmitter to the receiver wirelessly,which integrates power electronics technology,circuit theory,electromagnetic field theory,control theory and other technologies.Recently,CPT has received extensive attention from researchers because of its desirable characteristics of no sensitivity to surrounding metal objects and no thermal effects generated by the eddy current,low cost,light weight,and strong antimisalignment performance.In practical applications,such as powering consumer electronics,biological equipment,electric vehicles,etc.,some electrical equipment requires that the output of the CPT system is independent of the load and has the characteristics of constant current output.Besides,considering the security,the voltage stresses across the transmitter plate side and the receiver plate side of the capacitive coupler should be as small as possible under the premise of the active power transmission requirement.However,in the conventional double-sided LCLC-compensated CPT system,two external capacitors are required to be connected in parallel with the plates and there is reactive power transferred from the primary side to the secondary side,which will inevitably increase system complexity and lead to higher voltage stresses on the plates.Moreover,the CPT system is required to supply power to multiple electrical devices with the load-independent constant current outputs or constant voltage outputs,such as powering the light-emitting diodes(LEDs),batteries,reefer containers,etc.Multiple load outputs should be independent of each other to realize constant current,constant voltage,and power decoupling.However,the existing multi-load CPT systems do not fundamentally solve the power decoupling between multiple loads.Focusing on the problems that need to be solved in the existing CPT system,this thesis studies the single-load and multi-load CPT systems respectively.Focusing on the scenario of powering a single electrical device,this thesis proposes a novel double-sided LCL compensation topology design method.The voltage stress across the coupler plates is minimized with the constant current output.The number of compensation components is reduced.Focusing on the scenario of supplying power to multiple electrical devices,this thesis proposes the load-independent CPT system with multiple constant voltage outputs and constant current outputs.With the capacitive coupler and the compensation topologies design,the power coupling between multiple loads is eliminated.At the same time,the above-proposed system can always work at zero phase angle(ZPA).Specifically,the detailed work done in this thesis is as follows.For applications that require a constant current power supply to a single electrical device,this thesis proposes a novel double-sided LCL compensation method for the CPT system where no parallel-connected capacitors are required,thereby a stronglycoupled structure can be obtained with a constant current output and input ZPA characteristics.By keeping the phase angle difference between the voltage vectors across the primary and secondary plates at 90°,no reactive power is transmitted from the primary side to the secondary side.Thus,the voltage stresses across the plates can be minimized.The compensation topology parameters and voltage stress comparison between the proposed system and the conventional system are presented.The influence of the parasitic resistances on the system efficiency is given.An 80 W prototype with a coupling coefficient of 0.912 is established to verify the constant current output characteristics and the parameter design accuracy of the proposed compensation topology.The power loss comparison between the proposed design method and the conventional design method is given.An efficiency of 92.8% is achieved in the experimental prototype.For applications that require constant voltage power supply to multiple electrical devices,a novel load-independent CPT system with multiple outputs is proposed.The capacitive repeater unit is designed to enhance the power transfer capability,which contains four plates where two plates are used to receive power from its previous unit and the other two plates transfer power to the next unit.Electric coupling between the receiving and transmitting plates in the repeater unit can be eliminated by placing them perpendicularly and employing the split-inductor matching network.The load is connected with each capacitive repeater unit so that multiple loads can be powered simultaneously.Aluminum oxide ceramic is placed between the two adjacent units to enhance their electric coupling.The LCL-L network is adopted to compensate each capacitive repeater unit.Thus,constant voltage outputs can be achieved for all loads,which ensures the independent operation of each load.Considering the adjacent transmitter pair and receiver pair,a simplified equivalent model of the proposed capacitive coupler interface with multiple repeater units is established.The output voltages and efficiency are analyzed when considering the parasitic resistances.The influence of the compensation inductance variation and capacitive coupler tolerance on the system output voltages is given.Finally,a three-load experimental setup is built to verify the effectiveness of the proposed system with an efficiency of 93.2%.For applications that require the constant current power supply to multiple electrical devices,this thesis proposes a power relay system to wirelessly power multiple loads via capacitive coupling.The intermediate capacitive relay unit is designed to power the load as well as enhance the power transfer capability,which contains two receiving plates and two transmitting plates.It is proven in this thesis that the capacitive coupling between the receiving and transmitting plates in the same relay unit can be eliminated by being placed perpendicularly with the help of the proposed splitinductor-based compensation network.A general mathematical model of the multi-load capacitive power relay system considering all coupling capacitances is established.The L compensation circuits are employed to compensate the first and the last relays,while the LCL compensation circuits are designed to compensate the intermediate relays.Thus,the constant current output can be obtained for each load without affecting each other when neglecting the parasitic resistances.Additionally,the load current and efficiency variations versus the load resistance,coupling coefficient,and quality factor are thoroughly analyzed.Finally,a three-load experimental prototype is constructed to verify the feasibility of the proposed multi-load CPT relay system.The maximum efficiency can reach 86.1% at a power level of 37 W.