Design And Implementation Of Magnetic Coupling Resonant Wireless Charging System Based On Secondary Active Rectifier

Compared with the traditional wired charging technology,the magnetic resonance wireless charging technology has the advantages of high security,accessibility and hermeticity.During the charging process the equivalent load resistance of the battery is generally variable in real time.The system needs to be able to control and regulate the charging voltage and current in an accurately and timely manner.Nowadays,the commonly used method is to add a DC-DC converter at secondary side in order to regulate the output to satisfy the charging requirements.Although this method is simple to implement and reduces the complexity of the control,it increases the losses and reduces the efficiency of the system,as well as imposing a larger volume and cost.In order to improve system efficiency and reduce circuit size,the system in this thesis uses LCC-S resonant network,sets the primary side to an open-loop state with a steady frequency and duty cycle,and achieves closed-loop control using an active rectifier circuit only at the secondary side.The design eliminates dual-side communication,simplifies the circuit structure,satisfies the constant current or constant voltage output and achieves the objective of improving the efficiency of the system.Ultimately,the practicability of this design solution was confirmed by modelling and experimentation.The contents of this thesis are as follows:First of all,the working characteristics of the four basic compensation networks and several higher-order compensation networks are summarised.Then,the system is selected for an LCC-S compensated network topology because of independent operation at the primary side and open circuit operation at the secondary side.Next,the mutual inductance model is constructed to investigate the output and transmission characteristics.Secondly,the secondary side adopted a semibridgeless symmetrical structure as the active rectifier circuit structureon and introduced the four working modes in detail.The system is modeled and analysed with the compensation network topology,and expressions for the charging current and voltage,the equivalent impedance at the secondary side.Hence,the secondary side can adjust the charging voltage,current and the equivalent impedance by controlling the timing and conduction angle of the active rectifier circuit.Furthermore,the charging control strategy of the system is conceived to accommodate the charging curve of the battery.Thirdly,the design index of the system is obtained,and the design parameters and device selection of the system compensation network circuit,active rectifier circuit,secondary control circuit.And the software design are given,includes initialization configuration,anti-integral saturation PID control algorithm and charging management algorithmand the program structure of the control strategy are described.Finally,the constant current charging experiment,the constant voltage charging experiment and the constant current to constant voltage switching experiment show that the design of this thesis can achieve the effect of constant current and then constant voltage control output,which is in line with the charging curve of the battery.The peak efficiency of the whole machine was 91% and the maximum charging power was 148 W.As a result,the validity of the design of this thesis has been demonstrated.