Small Signal Modeling And Analysis For Wireless Power Transfer Systems

Wireless Power Transfer(WPT)technology has been widely studied by domestic and foreign scholars for the advantages of being independent of dust,chemicals,weather and other factors.The corresponding products e.g.,wirelessly powered household appliances,human implantable devices,electric vehicles and rail trains have got a preliminary development.In all product operation control,PI control is widely used as a classical control method.The performance of the controller directly affects the stability and the final quality of the product.In practice,PI controller parameters are often set poor due to the lack of accurate mathematical models.As a result,the PI controller has poor adaptability to running conditions.Therefore,it is necessary to study the mathematical model of WPT systems.In general,mathematical models derived by different modeling methods have different levels of complexity.The mathematical model with a higher level of complexity is usually more accurate,but complex representations bring some difficulties to the modeling process.An accurate mathematical model is the guarantee for the design of PI controller parameters.Generalized state-space averaging(GSSA)is an effective method to analyze the resonant converter.It can not only get the complete trajectory of the state variables quickly and accurately,but also can realize optimized designing and analysis for the WPT system.Thanks to the powerful analyzing and processing capabilities of modern computers,it is possible to design PI controller parameters for a complex mathematical model by means of a commercialized production with PI controller self-tuning function.The main work of the thesis can be summaried as follows:1)Small signal modeling and analysis of the WPT system based on LCL-S topology.Firstly,the large-signal model of the WPT system and the steady-state operating point are derived with the help of the GSSA technique.Based on the previous work,the small-signal model is established to describe how the load voltage will react to a perturbation in its input.Comparing the step response of the small-signal model with the output of the experimental setup,the small-signal model is nearly identical to the system dynamics.In other words,the proposed small-signal model can describe the prototype well.Then,the Matalab's PIDtool design toolbox is used to generate suitable PI controller parameters for a fast response time in the load voltage according to the small-signal model.Finally,experiments prove that the closed-loop digital PI controller is designed to ensure a fast response time in the load voltage step change.2)Small signal modeling and analysis of dual transmitters based WPT system.Firstly,the large-signal model of the IPT system,the steady-state operating point are derived using GSSA technique.Based on the previous work,the small-signal model is established to describe how the load voltage reacts to a perturbation in its input.Then,the Matlab's PIDtool design toolbox is adopted to generate suitable theoretical PI controller gains for a fast response time in the load voltage.Meanwhile,the phase angle stability margin of closed-loop small-signal model is verified accordingly.Finally,comparing the step response of the small-signal model with the simulink model and the experimental one respectively,the small-signal model proves to be closely matched to the WPT system's dynamics.The results come out to be consistent with the theoretical design and validate the accuracy of the modeling.