Control And Optimization Methods Of Dynamic Wireless Power Transfer System For Efficiency Improvment

Dynamic wireless power transfer(DWPT)systems based on inductive power transfer technology can charge the electrical vehicles and trams wirelessly and continuously when the vehicles are moving,reducing the capacity of on-board energy storage equipment and increasing the operation efficiency of the vehicles.DWPT technology with these advantages will be an ideal power supply solution in the future autonomous and intelligent transportation scenarios.However,one of the challenges during developing DWPT technology is to improve the system efficiency.This is because of two aspects.Firstly,in a specific DWPT system,the reveiver coil is in motion relative to the transmitter coil and therefore,the mutual inductance between the transmitter coil and the receiver coil varies greatly.The variation of mutual inductance will influence the power characters and the current disctribution of the DWPT system,consequently incrasing the power losses of each power stage and decreasing the overall system efficiency.The first challenge is to mitigate the effect of mutual inductance variation to improve system efficiency.Secondly,in a DWPT route with many transmitter coils installed,the transmitters are segmented in order to reduce the transmitter coil losses and to increase the system efficiency.However,the length of each segmented transmitter cannot be too short due to cost constraint and is related to the power level of the DWPT system and the vehicle speed,which is a complex problem considering the operation of DWPT system conditions.Thus,the second challenge is to find a proper segment length and allocation of DWPT transmitter coils to decrease coil losses while reducing total costs.The main focus of this thesis is therefore set on the efficiency optimization methods for DWPT systems to propose three efficiency optimization control methods for single transmitter single receiver DWPT system,dual transmitter single receiver DWPT system,and single transmitter dual receiver DWPT system respectively.In addition,an optimal planning method for segmented DWPT route is also proposed considering the mutltiple obejects optimization on total cost and system efficiency.The first part of this thesis proposes a new dual-side controller for single transmitter single receiver DWPT system in electrical vehicle(EV)dynamic wireless charging applications,which can maintan stable output power and optimize the system efficiency simultaneously,eliminating communication link and mutual inductance estimation in spite of the movement of receiver coil.A comprehensive circuit model is established to describe the power characters with various duty-cycles of the inverter and converter and to analyze the zero-phase-angle(ZPA)operation points of the inverter with respect to the controlled active rectifier.Based on the relationship between the ZPA condition and the maximum efficiency condition,a dual-side independent close-loop control method is proposed to regulate output power while optimizing system efficiency without communication link and mutual inductance estimation.The experimental results convincingly demonstrate the proposed control method in close-loop under dynamic conditions.The second part of this thesis proposes an optimal current ratio based efficiency optimization method for dual transmitter single receiver DWPT systems in autonomous guided vehicle(AGV)dynamic wireless charging applications,maintaining stable output power while improving system efficiency without mutual inductance estimation.A detailed circuit model is established to analyze the influence of the phase and amplitude of the dual transmitter currents on the output power and system efficiency.Based on the analysis,an optimal current ratio is found to satisfy the stable output power and maximum efficiency condition simultaneously.Moreover,an equivalent optimal input impedance ratio of the inverters is derived for close-loop control without mutual inductance estimation.Accordingly,a closeloop control strategy with master-slave switching control and current direction control is proposed.Experimental results demonstrate the validity of this control method.The third part of this thesis proposes an optimal load ratio based efficiency optimization method for single transmitter dual receiver DWPT systems in electrical tram dynamic wireless charging applications,maintaining stable output power while improving system efficiency without communication link and mutual inductance estimation.A comprehensive circuit model is established to desctibe the philosophy of adjusting the equivalent load ratio to achieve stable output power against the movement of the receiver.An optimal load ratio is found that can satisfy the stable output power and maximum efficiency point simultaneously.A closeloop control method is proposed and validated by daynamic experiments.The fourth part of this thesis proposes an optimal planning method of a single transmitter dual receiver DWPT route for tram's wireless traction power supply system,optimizing the total cost and system efficiency.Key factors and variables that relate to the system cost and system efficiency are analyzed.A mutlti-object optimization model is established,in which the coil parameters,the inverter paramters and the on-board energy storage capacity are the optimization variables.This model is solved by a PSO and traversal combined algorighm according to a three-section tram operation data,resulting a Pareto solution set.The optimized DWPT segment planning are compared with the stationary WPT charging scenario to show the advantages of the DWPT systems.This thesis investigeates several optimization methods for efficiency improvement of DWPT systems with various coil structures in various applications.Theoretical model and control methods are given for future application of DWPT systems.