Research On Key Issues On Multiple-Coil Wireless Power Transfer System

As a non-contacting power transmission technology,wireless power transfer(WPT)has the advantages of good security,high adaptability to the environment and convenience in application,etc.The WPT technique commendably meets the charging requirements of smart equipment and electric unmanned vehicles.As the main multiple-coil WPT technology,single-transmitter multiple-receiver WPT(STMRWPT)system and multiple-transmitter multiple-receiver WPT(MTMRWPT)system can respectively transfer electrical power to multiple terminals simultaneously and improve the power levels of the WPT systems,which is of great significance for engineering applications and scientific researches.However,at present,STMRWPT technology is confronted with the problems of efficiency optimization and power control.Concurrently,the synchronous control and cross-coupling effect of STMRWPT technology remain issues to be addressed.Moreover,the MTMRWPT system also faces the problems of current distribution,efficiency optimization,voltage control and cross-coupling effect elimination between coils.Aiming the problem mentioned above,researches are conducted on various aspects,and the contents of this dissertation are concluded as follows:(1)It is found that although STMRWPT system can achieve high system efficiency under impedance matching condition,it is difficult to meet the power requirements of loads.In this dissertation,a control strategy is proposed focusing on both efficiency optimization and power control.The principle of this strategy is:modulate the controlling angle of inverter at the primary side to optimize the system efficiency;modulate the controlling angles of active rectifier bridges at the secondary side to control the output power.Although the efficiency of the system is slightly about 0.3%lower than the impedance matching method,it can operate in a highly efficient area and provide target output power to multiple independent receivers.(2)The STMRWPT system with series-series compensation network has been analyzed in this dissertation.It is found that the synchronous control method of single-transmitter single-receiver wireless power transfer(STSRWPT)system is not applicable for STMRWPT system because the coupling voltages of multiple receivers are reflected to the voltage at the primary side,which makes it no longer has the phase relationship that currents at the secondary side lead voltage at the primary side u₁90°.In order to explore the compensation network applicable for STMRWPT system,The circuit characteristics of 16 kinds of main compensation networks are analyzed,focusing on the synchronous control,whether the coupling coefficient k can be zero and maximum efficiency tracking,etc.Finally,an independent synchronization control method based on dual LCL-S compensation network is proposed.Finally,a dual LCL-S compensation network for STMRWPT system is obtained,and based on the compensation network,a synchronization control method with multiple independent receivers is proposed.(3)A time-sharing control topology is proposed to solve the problem that cross-coupling effect weakens the performance of STMRWPT system.The time-sharing topology can effectively reduce the influence of cross-coupling effect on the system,improve the system efficiency and is applicable to the operating conditions with variant coil positions and loads.To solve the problem that the time-sharing control topology of the uncontrolled rectifier bridge is difficult to detect the zero-crossing point of the resonance current at the secondary side,the topology structure of the active rectifier bridge is proposed to replace the uncontrolled rectifier bridge,and the synchronous signal in the synchronous control process of the controllable rectifier bridge is used to automatically detect the zero-crossing point of the resonance currents at the secondary side.Finally,a voltage control strategy suitable for time-sharing control topology is proposed,which can transmit target output voltage for multiple receivers with different voltage levels simultaneously,as well as the requirements that each receiver circuit must work in impedance matching condition.A time-sharing control topology is proposed for STMRWPT system,which can effectively reduce the influence of cross-coupling effect on the system.To solve the problem that the time-sharing control topology of the uncontrolled rectifier bridge is difficult to detect the zero-crossing point of the resonance current at the secondary side,the topology structure of the active rectifier bridge is proposed to replace the uncontrolled rectifier bridge,and the synchronous signal in the synchronous control process of the controllable rectifier bridge is used to automatically detect the zero-crossing point of the resonance currents at the secondary side.Finally,a voltage control strategy suitable for time-sharing control topology is proposed,which can transmit target output voltage for multiple receivers with different voltage levels simultaneously,as well as the requirements that each receiver circuit must work in impedance matching condition.(4)In order to optimize the efficiency of MTMRWPT system,the efficiency optimization problem with multiple control variables can be decoupled into several independent efficiency optimization problems of STSRWPT system,so that the problem can be simplified.Moreover,a control strategy is proposed to balance the minimum current distribution,constant output voltage and efficiency optimization.In this strategy,the minimum current distribution function is the fitness function of the control strategy,and the constant output voltage is the constraint condition of the optimization algorithm.By adjusting the control angle of the active rectifier bridge,the system operates in the high efficiency area.Besides,the current distribution control is realized by particle swarm optimization algorithm.At last,a compensation method for cross-coupling effect of MTMRWPT system is proposed,which decouples the cross-coupling mutual inductances between coils into the impedances on the circuit for compensation,so that the voltage and current characteristics of the system can be equivalent to the voltage and current characteristics without cross coupling effect,and effectively simplify the complexity of the study.