Research Of Key Technologies On Design And Control For High Frequency Resonant Converters

Compared with the traditional pulse width modulation(PWM)converter,the resonant converter can effectively reduce the switching loss,so that the operation frequency can be further improved.The higher operation frequency of the converter,the smaller the transformer,inductor,and capacitor.In addition,the smoothly changing waveform and the smaller rate of change of voltage and current also help to improve the electromagnetic compatibility of the resonant converter.However,the resonant converter requires a resonant network composed of a certain number of inductors and capacitors,which makes its analysis and design more complicated.By carefully designing the resonant network,the resonant converter can obtain good performance at or near an operating point,and it is difficult to obtain good performance under a wide range of input voltage and load conditions.In addition,the tolerance and aging problems of the resonant network also bring certain challenges to the design of the resonant converter.This is because the inevitable manufacturing tolerances and aging problems of resonant components(inductors,capacitors)make the parameters of the resonant network deviate design value,the performance of the resonant converter drops.The resonant converter is usually controlled by the variation of switching frequency.In some schemes,the switching frequency adjustment range may be very large,which will cause a wide noise spectrum,difficult to control electromagnetic interference(EMI),and complex output.Shortcomings such as voltage ripple filter design and poor utilization of magnetic components.This paper takes the resonant converter as the research object,and studies the topology of the converter,the resonant network and the modulation control strategy.The resonant components in the resonant network of the resonant converter are optimized for design and control.Under the condition of a fixed switching frequency,the resonant frequency is adjusted by changing the capacitance or inductance to achieve the purpose of controlling the output of the resonant converter.Those methods can effectively broaden the operation range of soft switching,and at the same time thay can solve the problem of performance degradation caused by tolerance and aging of the resonant network,and improve the performance and reliability of the resonant converter.The main contents of the thesis include the following aspects:1.The control and operation analysis of the resonant converter are analyzed,the PWM modulation strategy of the resonant converter is studied.Then,the PWM modulation strategy of the resonant converter is studied and discussed.The traditional phase shift(PS)modulation strategy,the asymmetrical pulse width modulation(APWM)strategy and the asymmetrical voltage-cancellation(AVC)modulation are compared.The results show that the AVC control strategy can effectively reduce the fundamental harmonic phase of the square wave output voltage,thereby maximizing the phase difference between the voltage and current.The operation range of soft switching is improved,and the power conversion efficiency can be effectively improved compared to the other two modulation strategies.The correctness and feasibility of theoretical analysis are verified by simulation and experiment.2.The switch-controlled capacitor(SCC)and its tuning control is studied.First of all,it focuses on the operation principle of SCC and the corresponding control method.On this basis,the general analytical formula of equivalent capacitance value of SCC is derived theoretically.According to the control requirements of SCC,a method to accurately control SCC is proposed,and the corresponding control circuit is designed at the same time.Finally,the SCC tuning control resonant converter is designed and analyzed,and the effectiveness of the proposed scheme and control method is verified through simulation and experiment.3.A dual SCC tuning control resonant converter for wireless power transfer(WPT)is proposed.Firstly,the topology and operation principle of the proposed WPT system are introduced in detail,and the system is modeled and analyzed.By performing optimal AVC modulation and SCC tuning control on the resonant converter,it aims to optimize the transmission efficiency of the converter while achieving maximum efficiency tracking.Finally,a design application example is given,and the experimental results show that the proposed scheme and control method can effectively improve the efficiency of the system.4.The variable inductor(Variable inductor,VI)and its tuning control method are studied.First,the operation principle and control method of VI are studied,and VI is analyzed based on the magnetoresistance model.Then the output characteristics of series resonant converter and parallel resonant converter under VI tuning control are analyzed.Finally,the VI tuning control resonant converter of the WPT system is designed.Aiming at the change of the relative position between the transmitting side coil and the receiving side coil,through the VI tuning control,the stable output under the condition of gap change or misalignment is realized.The experimental results show that the proposed scheme and control method can effectively improve the efficiency of the system.In order to better grasp the resonant converter technology of SCC and VI tuning control,the advantages and disadvantages of SCC and VI tuning control methods are compared in terms of topology complexity,control difficulty and voltage gain adjustment range.So as to provide guidance for engineers in the analysis and design of resonant frequency modulation resonant converter.5.The last chapter summarizes the thesis and discusses the future works.