| The traditional magnetic wireless power transfer(WPT)technology usually only has one primary coil and one secondary coil.This one-to-one power supply mode which is mature nowadays brings portability and practicality to many small-power devices or devices with relatively stable charging environments.However,for some high-power application scenarios,the power level of the one-to-one mode is limited and needs to withstand greater voltage and current stress,and there is not enough flexibility in some application places,such as multi-degree of freedom wireless power transfer.The limitations of the one-to-one WPT system in the charging area have led people to adopt the coil array method to expand the charging range,and the method of connecting multiple transmitting coils in parallel with a single input source has responded.However,this method still cannot reduce the current stress of the switching device on the DC bus,and at the same time,the impedance change during charging may cause circulating current in the parallel circuit,which not only may damage the converter but also increase the control difficulty of the system.Therefore,multi-excitation unit wireless power transfer(MEU-WPT)technology is proposed to solve the problems of improving the power level of the WPT system and reducing the current and voltage stress of the primary switching device.At the same time,it can improve the flexibility of the system.Unlike the multi-coils WPT system,the MEU-WPT system not only has multiple transmitting coils,but each coil generally has an excitation source,and each excitation unit can work almost independently,which prevent the entire system from crashing.The MEU-WPT system is favored by many applications due to its high power capacity,flexibility,and low current and voltage stress,such as distributed track wireless charging cars,inspection robots,drones and wireless charging platform for mobile phone and so on.In the wireless charging process of various application scenarios,the change of the coupling coefficient during dynamic charging and the interference of environmental factors during static charging will have a greater impact on the working conditions and output characteristics of MEU-WPT.This thesis aims to solve the charging area analysis and identification problems of the MEU-WPT system and the design the optimal control strategy for different regions with optimal powe supply strategy,which can provide method reference and theoretical support for complex system design in practical applications.The main work and research content of the thesis as follow:(1)Charging area analysis and optimization method based on MEU-WPT systemAiming at the layout planning and utilization of coupling mechanism in MEU-WPT system,the charging area range and optimization design method of coupling mechanism are studied.Firstly,the circuit model of MEU-WPT system is established,and the characteristics of MEU-WPT system are briefly introduced,and the comparison between MEU-WPT system and traditional WPT system with single transmitter and single receiver is carried out.Secondly,based on the electromagnetic theory,the Neumann equation in three-dimensional coordinate system is established,and the change of mutual inductance coefficient of coupling mechanism under the condition of system circuit parameters is analyzed,and the output characteristics of the system in the region are transformed into intuitive color temperature diagram.At the same time,combined with Dowell model to calculate the loss of high frequency multi turn winding,the expression of charging area and its constraint conditions are further derived.Then,according to the application requirements of MEU-WPT system,the charging area which meets the output index is divided,and the theoretical identification method of charging area and non charging area is obtained.Finally,the multi physical field finite element analysis method is used to further optimize the design of the coupling mechanism to expand the charging area.This chapter is based on the principle of MEU-WPT system charging area analysis,which provides guidance for the following articles.(2)Identification of charging area for multi excitation unit WPT system based on dynamic coupling parameter detectionAiming at the position uncertainty of energy pickup mechanism in MEU-WPT system,a dynamic identification method of effective charging area and a control method of switching are proposed to make MEU-WPT system work in different power supply modes.Firstly,the coordinate system of dynamic charging process is established,and combining with the output characteristics of dynamic charging process,the judgment conditions of effective charging area are further simplified by using the functional relationship between mutual inductance and charging area.secondly.On this basis,a mutual inductance identification method for multi excitation elements is proposed.By analyzing the current relationship between DC side and AC side of MEU-WPT system,the real-time mutual inductance corresponding to each excitation unit is solved by combining equations.Then,based on the theoretical analysis,the design method of the area identification controller is given.The controller only needs the DC current information of the primary side and the load detection of the secondary side to realize the recognition of the charging area and the switching of the working mode.At the same time,the charging area can be adjusted dynamically according to the dynamic output power requirements,and the output voltage is stabilized by the secondary DC / DC converter.Finally,the feasibility of the theory is proved by experiments.(3)Optimal power allocation method for multi excitation unit WPT system with zero phase angle frequency driftAiming at the problem of zero phase angle frequency drift caused by indirect coupling of excitation units in MEU-WPT system,the output power regulation mode of zero phase angle frequency consistency of each excitation unit is studied.At the same time,in order to reduce the primary and secondary power converters as much as possible,a phase-shifting control method for current source resonant topology is proposed without adding additional auxiliary circuits And a ergodic control method for voltage source resonant topology is proposed to adjust the power of MEU-WPT system.Firstly,the realization conditions of zero phase angle frequency are analyzed for voltage source resonant topology and current source topology.Secondly,according to the change of dynamic parameters,the requirements of power allocation of different input sources are analyzed from the angle of maximum power frequency and zero phase angle operating frequency of each excitation unit.Finally,according to the theoretical analysis,different power allocation methods are adopted for different input sources,and the controller is designed,which provides a new idea for the power allocation mode of MEU-WPT system.(4)Optimal energy efficiency tracking method for MEU-WPT system based on identification of optimal / weak coupling regionsAiming at the complex energy efficiency allocation problem of MEU-WPT system in the effective charging area,in order to develop the MEU-WPT system which has the perception ability and the optimal energy efficiency allocation strategy to adapt to different effective charging area environment,an optimal energy efficiency control method based on the identification of the optimal / weak coupling area for MEU-WPT system is proposed.Firstly,the optimal efficiency matching condition of n-ary MEU-WPT system is analyzed by circuit modeling.Secondly,according to the environmental characteristics and output target,the effective charging area is further divided into the optimal coupling region and the weak coupling region,and the judging conditions of the optimal coupling region and the weak coupling region are given.Then,the energy supply targets of different effective charging regions are determined: when the secondary coil is located in the weak coupling region,the primary control objective of the system is to meet the rated power,while when the secondary coil is in the optimal coupling area,the primary control objective of the system is to achieve optimal efficiency tracking.Finally,in order to meet the high efficiency requirements in the whole effective charging area,an optimal energy efficiency control strategy is proposed,which only needs DC input current and duty cycle of DC regulator information to achieve the optimal performance of the system. |
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