Research On Constant Current–Constant Voltage Control And Magnetic Integration Technology Of Wireless Power Transfer Systems With Misalignment Tolerance

Electric vehicles have attracted widespread attention due to their environmental protection and energy saving characteristics.Compared to the conventional contact charging method,the inductive power transfer technology(IPT)has been widely researched due to its higher safety factor,more flexibility,more convenience,and easier integration of automation.The technology has become a potential future energy supply for electric vehicles.Therefore,the technology research has clear and practical significance.Based on summarizing current research backgrounds,this paper conducts in-depth research on the constant current-constant voltage control method,the magnetic integration structure of resonant components,and the expansion of misalignment tolerance for lithium batteries of electric vehicle charging systems.New solutions and technical supports for IPT systems are discussed and provided to achieve high efficiency power transmission.The main research contents of this paper are divided into the following four aspects:Aiming at the charging characteristics of lithium batteries,a high efficiency single-stage IPT charging system based on a variable inductor is proposed in this paper with a fixed operating frequency.For the first time,a variable inductor is applied to the IPT field to achieve constant current-constant voltage charging targets.The wide equivalent load variation range of lithium batteries and the wide misalignment range of loosely coupled transformers are two crucial problems which affect system power transmission characteristics.A constant current-constant voltage control strategy with a variable inductor is proposed.Through real-time control of the DC bias current on the control windings which are decoupled from the main power windings and closed-loop adjustments of the saturation depth of ferrite cores,constant current-constant voltage charging characteristics can be achieved effectively.By establishing circuit and magnetic models of the variable inductor,a resonant parameter design method to optimize the variable inductance variation range is proposed.Design processes of the system parameters and design guidelines of the variable inductor are given.Experimental results show that the IPT charging system proposed in this paper can realize wide misalignment tolerance with a variable inductor.Constant current-constant voltage output characteristics can be achieved by implementing the variable inductance as the only control variable without adding DC converters or power switches.The proposed system has characteristics of fixed switching frequency,low control complexity,high misalignment tolerance,and high system transmission efficiency.Aiming at the charging characteristics of lithium batteries,a high efficiency single-stage IPT charging system with a multi-band frequency tracking control is proposed in this paper.Under the condition of a fixed coupling coefficient,the analysis method and system parameter design criteria are proposed based on constraint derivation and topology network matching.The constant current-constant voltage charging characteristics with unity power factor can be achieved with a frequency switching control method.In order to expand the misalignment tolerance of the frequency switching control method,an IPT system with a multi-band frequency tracking control is proposed under the condition of a wide coupling coefficient variation range.The constant current-constant voltage output target can be achieved through closed-loop tracking control in multiple narrow frequency ranges.System reactive power can be minimized.Additionally,by analyzing the output characteristics of various compensation topologies,an optimal adaptive topology design method for the multi-band tracking control is proposed.Experimental results show that the IPT charging system proposed in this paper can achieve constant current-constant voltage output characteristics and wide misalignment tolerance with a multi-band tracking control.The proposed system has characteristics of clear parameter design,no additional components,narrow frequency adjustment range,strong adaptability,and high system transmission efficiency.Aiming at the balance of magnetic flux density and the improvement of system power density,a magnetic integrated structure design method for IPT systems based on spatial orthogonal nesting is proposed in this paper.The method nests single-sided and solenoidal coil structures and achieves orthogonal decoupling of the magnetic fluxes.Based on the design method,two novel magnetic integration structures are proposed in this paper.Aiming at the problem of large volume of resonant inductors in high-order compensation topologies,a magnetic integration structure of resonant inductors and power transmission coils is proposed based on radial and tangential orthogonal magnetic fluxes.Through circuit and finite element simulation modeling analysis,the system parameter design criteria to reduce the peak magnetic flux density in magnetic cores are proposed.Simulation and experimental results show that the magnetic integration structure proposed in this paper can eliminate the influence of cross-coupling under various misalignment cases and realize high power density,high transmission efficiency,and system magnetic flux balance.Furthermore,for systems employing multiple power transmission channels,a magnetic integration structure with dual power transmission coils is proposed in this paper based on transverse and longitudinal orthogonal magnetic fluxes.Through circuit and finite element simulation modeling analysis,a system control method by adjusting the operating sequence and multiplexing cross-coupling characteristics of the inverter is proposed.Simulation and experimental results show that the magnetic integration structure proposed in this paper can improve the power transfer capability of the system and achieve high power density,high transfer efficiency,and high compatibility.Aiming at the randomness of electric vehicle parking,a secondary side vehicle localization method is proposed in this paper based on the detection of comprehensive multiple coupling coefficients.An orthogonal nested magnetic integration structure is implemented.Based on the selectivity and symmetry of the structure,the three-dimensional position coordinates(x,y,z)of the vehicle when parked can be calculated with a surface fitting method.Circuit information on the receiving side can be obtained in the pre-charging stage.The position coordinates can facilitate the correction for the parking misalignment of electric vehicles.Experimental results show that the positioning method proposed in this paper is compatible with power transmission channels and has the characteristics of no auxiliary sensors,low number of auxiliary coils,good system compatibility,and high positioning precision.Additionally,in order to enhance misalignment tolerance,a single-stage IPT charging system based on the coupling complementary principle is proposed in this paper with a fixed operating frequency.By combining solenoidal and double decoupling winding structures,a method to realize wide misalignment tolerance is proposed based on the coupling complementary characteristics of magnetic fluxes.Circuit topologies and design guidelines which are suitable for the principle are given.Experimental results show that the IPT system based on the coupling complementary principle proposed in this paper can enhance the coupling coefficient for misalignment cases and improve the system power transfer capability.