Research On ICPT Topology With Constant Current And Constant Voltage Feature

Inductive coupled power transfer(ICPT)is a non-physical contact power supply technology,which can achieve power transmission through the air based on electromagnetic induction.This technology eliminates the shackle of cables and has better application prospects in the charging field of electric vehicles and underwater detection equipment for its convenience and high efficiency.In view of the current application requirements of the two-stage charging method of constant current and constant voltage for battery charging,the following three schemes are mainly used in the industry:(1)Frequency modulation or phase shift modulation,the critical disadvantage of this scheme is that the communication is required to complete the control information interaction between the transmitter and the receiver;(2)Cascaded back-end DC/DC converters,although this solution can obtain the better output performance,the insertion of the cascade converter greatly reduces the conversion efficiency of the whole system;(3)Switching compensation topology,this method needs additional ac switches and more compensation devices.Therefore,complex circuits,difficult design,and high cost are the common shortcomings of the above three solutions.In order to solve the above problems,firstly,a circuit based on S-S compensated topology with four coils is proposed in this paper,of which the transmission characteristic and input impedance characteristic can be analyzed in detail based on the controlled source circuit model.Research result shows:(1)Constant current or constant voltage output can be realized under different load conditions when the working frequency is equal to the resonant frequency of the circuit;(2)Based on appropriate parameter design,it is possible to achieve natural and smooth switching from constant current to constant voltage output within the expected load range,therefore,it has the advantage of simple control without additional controller;(3)Zero phase angel(ZPA)characteristics of the system input impedance can be ensured in both constant current and constant voltage output mode,for which the additional loss by reactive power circulation can be reduced,consequently it is conducive to realize efficient transmission of energy.Then the two primary coils of the circuit of Series-Series compensated topology with four coils are decoupled and equivalent,which can be regard as a new circuit structure based on hybrid compensated topology with four coils.In order to ensure that the transmission characteristics of the circuit remain undifferentiated between the equivalent circuit and original one,the mutual inductance model and the “T” equivalent model are used to analyze the two-port characteristics of the primary coils to obtain the calculation method of the compensation circuit.Finally,it is analyzed and demonstrated that the circuit has the ability to work normally without protection and detection circuits under the conditions of short-circuit,open-circuit at the load end or no secondary receiving coils,thus the system has higher reliability.Due to the different requirements to design magnetic couplers of the two proposed circuit topologies with natural constant current and constant voltage,this paper presents magnetic coupler design schemes for S-S compensated circuit topology with four coils and hybrid compensated circuit topology with four coils,respectively.Although the two circuits have no difference in terms of transmission characteristic and impedance characteristic,the difficulty of overall system implementation is different due to the different design requirements of the magnetic coupler.Therefore,the two schemes are compared in terms of the difficulty of coil design and parameter design freedom of the compensation circuit,and it is determined that the hybrid compensated circuit topology structure with four coils is better and has lower system implementation difficulty.Finally,a 3kW wireless power transmission prototype with four coils based on hybrid compensated topology was built in the lab.The experimental results show that the current deviation range is only-1.6%～4.3% in the charging simulation with constant current 10 A while the voltage deviation range is only-1.6%～5.7% in the charging simulation with constant voltage 300 V.The system transmission efficiency reaches 94.8% with a 100 mm transmission distance under full load condition.Experiments prove that the topology studied in the thesis can achieve smooth switching from constant current to constant voltage output mode with a faster response speed while feedback control is eliminated,which verifies the correctness and feasibility of the research scheme.