Research On Electric-field Coupled Wireless Power Supply Technology For Movable Devices

Electric-field coupled power transfer(ECPT)technology uses high frequency electric field as energy medium and integrates power electronics technology,circuit theory,control theory and technology to realize power transmission without direct electrical connection.In the applications of wireless charging for movable devices using ECPT technology,the pickup of the system often needs to be removed and moved back.In practical applications,it is required that the semiconductor switches in the inverter of the ECPT system are well protected from overcurrent and overvoltage whether the pick-up is removed or moved back.The power transfer system can automatically enter standby mode when the pick-up is removed and restore to deliver required power to the load effectively after the pick-up is moved back.In addition,many electrical equipments require constant output voltage of wireless charging system under a certain range of coupling capacitance and load changes.On the one hand,the removal of the pickup corresponds to a wide range of changes in system load.On the other hand,the removal of the pickup will change the topology of the ECPT system,which will greatly change the working characteristics of the ECPT system.The following problems exist in the process of removing the pickup of the existing ECPT system: 1)removal of the pickup causes sudden changes to the voltage and current of the inverter,which can easily damage the switches and lead to system collapse;2)after removing the pickup,the input power of the system is large and it can not work at standby state,which is not conducive to energy saving and emission reduction.Therefore,the electric-field coupled wireless power supply technology for movable devices needs to be studied urgently.This paper focuses on the research of wireless power supply technology for movable devices based on electric field coupling,including the working characteristics of the inverter,resonant network topology,system parameter design and output control under the change of coupling capacitance.Specifically,the research work contains:Aiming at the problem that the random removal of the pcikup results in current and voltage spikes on the switch of the ECPT system based on class E inverter,which makes the system cannot work properly and the system unable to work at standby mode after the removal of the pickup.This paper analyses the causes of the current and voltage spikes of the inverter caused by the removal of the pickup.Based on the same equivalent circuit of the system with pickup and no pickup,the condition for realizing wide load ZVS operation of ECPT system is given.A system design method which can effectively suppress the current and voltage spikes of the inverter caused by the removal of the pickup is proposed.The system can realize ZVS operation in wide load range at a fixed working frequency,thus the load adaptability and capability of ECPT system is improved.In order to realize the standby operation of ECPT system after removing the pickup,a power regulation method is presented.Finally,the feasibility and validity of the proposed system design method and power regulation method are verified by simulation and experiment.Aiming at the particularity of over-voltage and over-current in the ECPT system based on class E inverter and the shortcoming of its power regulation method,this paper analyses the causes of over-voltage and over-current in ECPT system using full-bridge inverter.Based on the characteristics of LCL resonant network,an F-type compensated ECPT system topology is proposed,and the models of ECPT system under full load and no load are established by fundamental approximation method.The working characteristics of the system are analyzed,and the design method of the main parameters of the system is presented,which can effectively restrain the current and voltage spikes of the inverter caused by the removal of the pickup and enable the power transmitting side to enter the standby state automatically when no load occurs.Finally,the feasibility and validity of the proposed ECPT system topology and its parameter design method are verified by simulation and experiment.The ECPT system can automatically work at standby state after the pickup is removed without any additional detection and control circuits.When the pickup is moved back,it can provide the required power for the load efficiently and steadily.The proposed system does not generate high overcurrents and overvoltages when the pickup is removed.In view of the fact that the resonant network of F-type compensated ECPT system does not have the boost function and can not enhance the output voltage of the system by designing the parameters of the resonant network and the requirement of the constant voltage output characteristic of the system in practical application,a boost-type ECPT system based on T-type CLC resonant network is proposed in this paper.The characteristics of T-type CLC resonant network are analyzed,and the expression of system output voltage independent of load is derived.The output voltage is equal to k times the input voltage of the system.The steady state models of the system under full load and no load are established and the working characteristics of the system are analyzed.The design method of system parameters considering both full load and no load characteristics and boost function is given.Finally,the feasibility and validity of the proposed ECPT system topology and its parameter design method are verified by simulation and experiment.Compared with the F-type compensated ECPT system,the ECPT system can achieve the same power transmission with lower input voltage under the same coupling mechanism parameters,system operating frequency and load.Aiming at the problem that it is difficult to ensure that the equivalent capacitance of the coupling mechanism before the removal of the pickup is exactly the same as that of the coupling mechanism after the next relocation of the pickup,which leads to the fluctuation and reduction of the output voltage of the ECPT system,this paper takes the ECPT system based on T-CLC network as the research object,focusing on the high-order,non-linear and multi-mode of the ECPT system.According to the characteristics of the interaction between continuous time and discrete state,the hybrid automata model of the ECPT system is established according to the theoretical method of hybrid system,and the boundary transition conditions of the working modes of the system are obtained.Thus,the control problem of the system is transformed into the selection of boundary transition conditions.Finally,simulations and experiments are carried out to verify the feasibility and validity of the proposed hybrid control method.