| According to the statistic data of carbon emission during 1990 and 2020,the meteorologist predicts that the global temperature will rises over 3℃ at 2100,leading to climate disaster accompanying with genocide.To realize energy conservation and emission reduction,our country is striving to increase the proportion of non-fossil energy consumption,such as wind power,photovoltaic power,hydropower and nuclear power,to 15.9%by 2020,meanwhile,about 48.4%of the carbon emission intensity is reduced when comparing with 2005.To coordinate with the transformation of energy structure,new energy vehicles,kitchen appliances and other products that driven directly by electric energy have developed rapidly.However,due to the harsh operation environment,such as wind and rain,bitter cold or torrid heat,the sealing problem caused by circuit aging and highfrequency plugging or pulling will introduce the users’ electricity risk.Wireless power transfer(WPT)technology employs high-frequency alternating electromagnetic field to realize non-contact energy transmitting,therefore,the safety can be effectively increased due to the higher airtightness.For a typical WPT system,DC voltage source needs to be inverted into high-frequency AC voltage source.As the quality factor of the WPT network which is positively related to system efficiency and the ability to decrease electro-magnetic interference(EMI),a higher frequency is always desired in theory,however,as there is unavoidable stray capacitors in the switches of the inverter,it will also introduces additional switching loss in practical.Additionally,as the output power is sensitive to the relative location of the transmitting and receiving coils,constant voltage/current control circuit which is disadvantage to the cost and efficiency is necessary for system safety.Class-E inverter and rectifier are potential due to their zero voltage switching(ZVS)feature and concise structure,however,as rigid conditions are required for ZVS realization and the switches will suffers from a high voltage stress,these topologies can only be employed in applications of miniwatt and low power adjusting freedom,contrary to the high flexibility of WPT technology.In terms of these drawbacks,active clamping and active resonance technologies are employed in this article to weaken the voltage stress on the switches,realize power adjusting ability by fewer components while enlarging the ZVS realization region.The main tasks are as follows:(1)An active clamped class-E inverter is designed to decrease the voltage stress while decoupling the voltage stress from extra factors such as the coils distance and load variation,as a result,the system stability and safety are enhanced.During the design process,the series-series(SS)and series-parallel(SP)WPT networks are modeled and compared,the resonant limitation on SP structure is calculated and the critical ZVS condition of the proposed topology in SP network is analyzed.In addition,the duty cycle of the switch also becomes adjustable in this topology,therefore,the relationship between duty cycle and output power is further calculated.(2)Class-E inverter uses the resonant current of the transmitter to extract the charge in the shunt capacitor of the switch for ZVS,namely,there is large phase difference between the current and input voltage of the resonant circuit,leading to a weakened power transfer ability.Furthermore,ZVS will be lost when the current becomes small.To decrease the phase difference while exploring the ZVS region,an auxiliary resonant circuit to provide additional current for charge extraction is introduced on the basis of active clamped class-E inverter.By approximately designing the impedance of the auxiliary circuit,the phase and amplitude of the addition current can be controlled to fit the ZVS condition while reducing the dependence on the coil’s current.After analyzing the power transfer ability and system efficiency,the two different parameter design strategy is given:if the WPT network is in complete resonant state,a large ZVS region can be realize,or else,if the WPT network is in weak inductive state,a full-range ZVS feature can be realized even through the power transfer ability is lower than the other strategy.(3)A switching capacitor based class-E rectifier is designed.By adaptively controlling the operation time of the switch,the conducting time of the diode in the class-E rectifier becomes adjustable,therefore,the rectification and power regulation ability are successfully fused together,namely,the system components becomes much fewer than typical strategies of active full-bridge rectifier and DC-DC converters,as a result,the cost,power density is effectively enhanced.The relationship between the conducting time of the diode and output power is calculated,the result reflect that,different from existing active rectifiers that can only decreasing the output power,the proposed topology can both rise and drop the output voltage.(4)An equivalent capacitor requires no additional detection and control circuits is built based on the current superimposing principle.When the system diverts from resonant state,corresponding equivalent capacitane will changes adaptively to ensure the transmitter return to the zero angle state(ZPA)to obtain a higher output power.Therefore,the proposed topology can eliminate the reactance caused by the changing conducting time of the diode in the active class-E rectifier and the power transmitter ability is maximized. |
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