| Magnetic coupling wireless power transfer technology uses an alternating magnetic field as the energy transmission carrier and is one of the most concerned wireless power transfer methods at home and abroad.In practical applications,in order to match the load characteristics of various types of electrical equipment and ensure the normal operation of the equipment,the magnetic coupling wireless power transfer system is required to output constant power or constant current and voltage.However,the change in the coupling coefficient will cause the outputs of the magnetic coupling wireless power transfer system to be unstable,and it is often difficult to keep the coupling coefficient constant in practice.For example,the misalignment of electrical equipment and the increased spatial freedom of wireless power transfer will lead to changes in the coupling coefficient.Therefore,how to overcome the problem that the output characteristics of systems are easily affected by the change of the coupling coefficient has become a key technology in the development of magnetic coupling wireless power transfer.The existing technologies mainly focus on magnetic coupling mechanism design,compensation network design,and closed-loop control based on wireless communication or parameter identification.However,there are still problems such as complex structure,poor antiinterference performance,slow dynamic response,and low cost-effectiveness.Therefore,based on the magnetic coupling autonomous circuit,magnetic coupling autonomous wireless power transfer systems with high misalignment tolerance or load independence are constructed in this thesis.Besides,the zero-phase-angle control strategy and its implementation method based on the transmitter-side information and single-stage inverter are studied for constant power,constant current,and constant voltage output.It is expected to break through the limitations of existing technologies and promote the practical application and commercialization of magnetic coupling wireless power transfer technology.The following work has been carried out in this thesis:(1)The basic structure of the series-series magnetic coupling autonomous circuit is presented,and the principle of zero-phase-angle control is expounded.It is pointed out that the magnetic coupling circuit with zero-phase-angle controlled AC power supply as the excitation source is an autonomous circuit.The mathematical model of the magnetic coupling autonomous circuit based on zero-phase-angle control is established,and its basic characteristics are analyzed.The research results show that the zero-phase-angle controlled magnetic coupling autonomous circuit can achieve constant current or voltage gain,constant output power,and constant transfer efficiency independent of the coupling coefficient in the strong coupling region,and has a strong misalignment tolerance.(2)A zero-phase-angle control method based on dual-mode switching is proposed,and the misalignment-tolerant constant-power characteristic of the autonomous wireless power transfer system controlled by this method is analyzed.By switching between the self-oscillating mode and PWM mode,the constant output power is achieved in a wide coupling range.At the same time,based on the reflection resistance,a method to distinguish the strong and weak coupling region is proposed to ensure reliable mode switching.Finally,the system is built and experiments are carried out to verify the theory.The research results show that the proposed system can achieve constant output power independent of the coupling coefficient in both strong and weak coupling regions,which effectively improves the misalignment tolerance of the system,and only the information on the transmitting side is needed during the control process,which is easy to realize.(3)A zero-phase-angle control method based on hybrid frequency modulation is proposed,and the misalignment-tolerant power-adjustable characteristic of the autonomous wireless power transfer system controlled by this method is analyzed.The output power is regulated by configuring the number ratio of two drive pulse signals with different frequencies.At the same time,the conditions for achieving soft switching are studied.Finally,the system is built and experiments are carried out to verify the theory.The research results show that the proposed system can achieve a controllable constant output power independent of the coupling coefficient and the soft-switching operation of the inverter can be maintained,without the DC-DC converter and dual-side communication,which effectively improves the system efficiency and control flexibility.(4)A zero-phase-angle control method based on phase shift is proposed,and the misalignment-tolerant constant-current characteristic of the autonomous wireless power transfer system controlled by this method is analyzed.The method of realizing misalignmenttolerant constant-voltage output is studied,and a control strategy for output constant current and voltage using only the transmitter side information is proposed.Finally,the system is built and experiments are carried out to verify the theory.The research results show that the proposed system can achieve constant output current and voltage independent of coupling coefficient and load resistance only based on a single-stage inverter,and the constant current mode can be switched to constant current mode automatically.In addition,the output current and output voltage are only related to the self-inductance ratio of the coupled coils,which significantly reduces the influence of self-inductance variation on the outputs.(5)A zero-phase-angle control method based on the harmonic operation is proposed.By transmitting energy through the harmonic,the switching frequency of the inverter can be significantly reduced.The mathematical model of the autonomous wireless power transfer system based on the harmonic operation is established,and the working frequency and output characteristics of the system are analyzed.At the same time,the influence of the fundamental component and other harmonics is studied.Finally,the system is built and experiments are carried out to verify the theory.The research results show that the proposed system can achieve constant output current and voltage independent of coupling coefficient and load,and has a high step-down conversion ratio.Therefore,when the low output voltage is required,there is no need to cascade dc-dc converter at the front end of the inverter to adjust the dc bus voltage,which can significantly reduce system costs and losses. |
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