Study Of Key Technologies In Very High Frequency Resonant Power Converters

With the rapid development of electric vehicles,data centers,and consumer electronics,demands of power converters for various electronic devices are increasing dramatically.At the same time,high requirements are placed on the size,weight,and cost of power systems.Increasing the operation frequency of switch mode power supply can reduce the energy storage requirements of passive components in power systems,thereby reducing the size of the energy storage components and improving the power density.However,switching loss in conventional power converters increases with the operation frequency,which degrades the power efficiency seriously.Very high frequency resonant topology can realize soft-switching and reduce the switching loss with resonant network.But unoptimized resonant parameters will lead to high switch voltage stress and circling currents,which will degrade reliability and efficiency of the converter.Furthermore,state of the resonant network depends on operation conditions of the converter.When the operation condition deviates from the optimal point,soft-switching failure and large reverse conduction loss may occur.To achieve soft-switching under dynamic load,existing control method operates the converter intermittently,which causes large output voltage ripple.To address above issues,this thesis studies voltage stress reduction,efficiency improvement and output voltage ripple reduction methods for very high frequency resonant power converters from the aspects of resonant parameter design and control optimization.Firstly,to address the high switch voltage stress and circling loss caused by resonant network,a parameter design strategy is proposed for classФ₂ inverter based on harmonic weighting and target function method.The proposed design method simplifies the design procedure,minimizes the switch voltage stress,and reduces circling loss of the resonant network.By optimizing harmonic weighting of the switching node voltage,the target switch voltage with minimized peak value is obtained.With the result,branch currents and the switching node impedance characteristics to achieve the target switch voltage are derived.In addition,by analyzing the influence of resonant parameters on branch currents,basic constraints of the resonant network are obtained to reduce circling loss of the inverter.Combining the impedance characteristics and basic constraints of the resonant network,the resonant parameters are directly calculated,which minimizes the switch voltage stress and circling loss.A 27.12 MHz classФ₂ inverter prototype is built.Compared with conventional design,the prototype reduces the switch voltage stress by 10.2%and improves the power efficiency by 7.2%.Then,to reduce the high reverse conduction loss of gallium nitride high electron mobility transistor in classФ₂ inverter,this thesis proposes a reverse conduction time compensation strategy based on spectrum quantification method and linear equivalent model.The power switch is modeled as a current source according to the time-domain analytical expressions of branch currents,which simplifies the circuit to a linear network.By quantitatively analyzing the spectrum characteristics of the current source and calculating response of the linear network under the current source excitation,analytical expressions of the switching node voltage under different operation conditions are derived.Based on zero-crossing point of the switching node voltage,the optimal duty ratios under different operation conditions are obtained.With the results,the compensation strategy is proposed.Experimental results show that the proposed method improves the power efficiency across the whole load and input voltage range,and achieves a peak efficiency of 93.6%at full load.Finally,to address the problem of soft-switching failure and high reverse conduction loss under pulse frequency modulation and rectifier load,a boundary duty ratio pulse frequency modulation control is proposed based on a resonant fitting model.With descriptive function of the rectifier and impedance fitting for the resonant network,the resonant fitting model is established,and the boundary duty ratio to achieve zero voltage switching is derived.With the result,the boundary duty ratio pulse frequency modulation control is proposed,which ensures zero voltage switching and prevents reverse conduction of the gallium nitride high electron mobility transistor under dynamic switching frequency.In addition,small-signal model of the power converter under proposed control is derived to provide theoretical guidance for control loop design.At light load,the mixed-mode controller switches the control mode to ON/OFF modulation,which extends load range of the converter.Compared with conventional control,the power loss is reduced by 33.3%at 40%load,and the output voltage ripple is reduced by89.1%at full load.The research results show that,based on high-speed power semiconductor devices,soft-switching power conversion topology,and novel control strategies,very high frequency power conversion techniques can overcome the bottleneck in the development of conventional switch mode power supply.By increasing the operation frequency above 10 MHz,very high frequency power converters can significantly reduce the size of passive components in power converters,which promotes the miniaturization and integration of power systems.