Research On Buck-Boost-LLC Single-stage AC-DC Converter

In order to reduce the harmonic pollution of the power electronic device to the power grid,the AC-DC converter needs to have a power factor correction(Power Factor Correction,PFC)function.The traditional two-stage AC-DC converter has complicated control and high circuit cost,so in low-power applications,the single-stage AC-DC converter has become a research hotspot.Single-stage AC-DC converters can achieve power factor correction,low voltage output and electrical isolation,but it is difficult to take into account PF value,efficiency,wide input voltage and bus voltage stress.In order to broaden the input voltage range of the single-stage AC-DC converter while taking into account the efficiency,PF value and low Bus voltage stress,From the topological point of view,this dissertation integrates the cascaded Buck-Boost converter and LLC converter through the multiplexing of switches,and proposes a single-stage Buck-Boost-LLC AC-DC converter.From the control point of view,the PFM/PWM hybrid control strategy based on DFC and the control strategy based on TSC are introduced.The working mode,basic characteristics,principle and algorithm realization of the converter are analyzed in detail.The thesis firstly integrates the cascaded Buck-Boost converter and LLC converter through multiplexing of switches,and proposes a single-stage Buck-Boost-LLC AC-DC converter.The working principle,different working modes and basic characteristics of the converter are analyzed,and the constraints for the LLC unit to realize soft switching are deduced.The existing problems under modulation lay a theoretical foundation for the introduction of the subsequent hybrid control strategy and the parameter optimization design of the converter.Secondly,based on the power balance analysis,the DFC-based PFM/PWM hybrid control strategy is introduced,the basic principle of DFC and the corresponding hybrid control are introduced in detail,and the key working waveform,control principle and algorithm implementation are detailed;The parameters of the converter are designed,and the relationship between the key variables and the effective value of the input voltage is theoretically analyzed.Finally,an experimental prototype is built to verify the correctness of the theoretical analysis.Finally,a control strategy based on TSC is introduced for the proposed converter,and the basic principle,system control strategy,key working waveform and algorithm implementation of TSC are introduced in detail.Finally,an experimental prototype is built,and the theoretical analysis is tested to verify its correctness.