Research On Multivariate Nonlinear Feedback Control Of The Wireless Power Transfer System

Wireless Power Transfer(WPT)is widely used in electric vehicles(EV),high-voltage line monitoring equipment,tailless home electrical equirpment,wireless sensor networks,implantable medical device,oil and gas wells,underwater electrical equipment and other fields because of its convenience and safety.However,in the process of wireless charging,the system will be disturbed by the parameters of the load and the coupled interference between each control-loop,resulting in an inevitable deviation of the output current/voltage and zerovoltage-switching(ZVS)angle,which brings challenges to the system.In this paper,the multivariate WPT system was taken as the research object.Firsty,the dynamic mathematical model for each control-loop was established.Based on the model,the output current/voltage feedback controllers and ZVS angle feedback controller were proposed and designed to improve the dynamic performance of the WPT system under the load parameter disturbance.Then,the coupled interference between each control-loop was analyzed in a multivariate application scenario.A decoupled compensator was designed to eliminate this coupled interference.Finally,a spatial linear transformation law was obtained and used to realize the precise linearization,and design a nonlinear controller for the WPT system.Simulations and experiments show that the dynamic performance of the system was improved when the load and operating point are offset.The specific work is as follows:(1)To realize the feedback control of a multivariate WPT system,the output current/voltage feedback controller and ZVS angle feedback controller of the system are designed respectively in this paper.In the control of the output current/voltage of the system,aiming at the high-order and communication delay problems in the dynamic modeling analysis and feedback controller design process of WPT system,a reduction method based on the state-space balance realization and a discrete delay link were adopted.The parameters of the output current/voltage controller were designed according to the analysis result of the dynamic performance.In the contorl of the ZVS angle of the system,a nonlinear model with the ability to describe the dynamic performance of the ZVS angle was established,and linearized based on the small signal linearization method.Because of the dynamic performance is related to the distribution of the system dominant pole in the s-plane,the parameters of the ZVS controller were designed by calculating the time constant of the closed-loop dominant poles.During the experiment,the designed feedback controllers of the multivariate WPT system were verified when the load resistance step changes.(2)To overcome the problem of the coupled interference between the output current/voltage control-loop and the ZVS angle control-loop,a decoupled control method was proposed in this paper.Take the application of wireless charging of EVs as an example,two nonlinear dynamic models with the DC voltage of the inverter as the input and the output current/voltage and ZVS angle as the output were established in the constant current and constant voltage modes.After the models were linearized based on the small signal linearization method,the relative gains of the linear model were obtained and used to design feedforward decoupling compensators.Finally,the parameters of the feedback controllers were designed respectively according to the required dynamic performance index of the WPT system.And the constant current and constant voltage decoupling control were verified in the experiment.(3)Because of the parameters of the feedback controllers in each loops were desinged according to the small signal linearization models,this will cause the dynamic performance perturbation of the system when the operating point is offset.So this paper proposes a WPT system dynamic modeling and precision linearization nonlinear control method based on the affine nonlinear theory.By using the equivalent reflected impedance of the secondary side at different resonance state,this paper further simplifies the WPT system circuit and establishes a low-order equivalent affine nonlinear mathematical model.After the exact linearization condition of the model was verified,the integral curve was used to solve the coordinate mapping law of the linear model.Finally,by designing the output feedback controller of the linear model and mapping it into the nonlinear coordinate system,the nonlinear controllers of the system were abtained.Both simulation analysis and experimental verification prove that the nonlinear control method can maintain a bether dynamic performance when the system operating point shifts.