Research On Effciency Optimization Of Wireless Power Transfer System Using A Z-source Converter

The power transmission source of the magnetic coupling resonance wireless power transfer system mostly consists of a bridge topology,so that its output voltage can only be adjusted below the bus voltage,which greatly limits the power output capability and voltage adjustment capability of the system.In order to solve the above problems,a quasi-Z-source inverter is applied to the wireless power transfer system in this article,which expounds and analyzes its basic working principles and control methods,and discusses the system control and efficiency optimization issues.The quasi-Z-source inverter completes the function of boosting and inverting by controlling the subsequent H-bridge switching devices.Under the sine pulse width modulation method,the shoot-through state can be inserted into the zero vector,so as not to affect the output,pumping up the bus voltage at the sime time.However,the square wave inverter mode is generally adopted in the wireless power transfer system,and its shoot-through state needs to be realized by adjusting the driving sequence and pulse duty cycle,which is described in detail in this paper.Further,a detailed analysis of the working mode and mode of the entire quasi-Z-source inverter network has been carried out to fully pave the way for the device parameter design.Due to the large number of dynamic components and the complexity,the dynamic modeling of wireless power transmission systems has always been a difficult problem.The generalized state-space average modeling method is suitable for wireless power transfer systems because of its fast time-varying characteristics.Based on this,Fourier coefficients and switching functions is introduced to connect the state variables of the circuit with the generalized state variables,a large-signal model of the system is established in the shoot-through and phase-shift control mode,and the transfer function model of the system is further derived with the help of the small-signal perturbation method.The model is used to analyze the steady-state and dynamic characteristics of the system,which provides an important reference for the design of the system controller.In the process of system efficiency analysis,traditional methods mostly ignore the losses of the primary and secondary power converters,which makes the analysis results unsatisfactory.In this paper,the losses of the inverter and rectifier are included in the efficiency model,and the maximum power point and optimal efficiency point of the system are analyzed by the method of loss resistance approximation.The influence of each system parameter on the optimal efficiency point is obtained.The simulation results prove that the efficiency analysis model can guide the system to find the optimal efficiency point with higher accuracy.In this paper,an experimental platform for wireless power transfer system using Z-source converters is built,and the basic principles and theoretical models of the system are experimentally verified through digital PI controllers.The results show that the theoretical model has sufficient accuracy and the system is controlled at optimal efficiency.Under the strategy,the system efficiency can be effectively improved.