Research On DC-DC Converter In Vehicle Auxiliary Power Module

With the shortage of non-renewable energy such as oil and air pollution problems have reached the point that cannot be ignored,in the aspect of transportation,green travel has gradually become a consensus.In this context,Electric Vehicle(EV),due to its excellent safety,comfort and environment-friendly characteristics,has attracted attention from all aspects,promoting the upsurge of relevant research and applications.In the electric system architecture of EV,an auxiliary power module(Auxiliary Power Modules,APM)DC-DC power converter is required to transfer power from the power battery to the low-voltage load to meet the power demand of low-voltage equipment.Such converters should have good reliability,stability,and high efficiency.The thesis first classifies the existing DC-DC converters suitable for vehicle-mounted APM at the topology level,then analyzes the specific topology and its advantages and disadvantages.Secondly,the loss sources of DC-DC converters and their efficiency improvement methods are summarized.Finally,aiming at adapting to wide-range voltage input/low-voltage high-current output and high efficiency,the feasible topologies for vehiclemounted APM DC-DC converter is studied.The main research contents of this thesis are as follows:(1)According to the characteristics of high-voltage input/low-voltage high-current output of the vehicle-mounted APM DC-DC converter,the modular combination of inputseries-output-parallel is selected as the main structure of the converter,and a new topology of DC-DC converter based on this structure is studied.The sub-module selects a Phase-Shifted Full-Bridge(PSFB)DC-DC converter based on current-double synchronous rectifier,and introduces an auxiliary LC circuit to widen the voltage input range of the converter.while the lagging arm switch can also achieve zero voltage switching(ZVS)under light load conditions;The common-duty-ratio control strategy is adopted to reduce the complexity of control on the premise of ensuring input voltage sharing and output current sharing.The designed converter effectively reduces the voltage stress of the high-side switching,reduces the duty cycle loss,and improves the efficiency at light load.Finally,the feasibility of the proposed converter is verified by experiments.(2)In order to further improve the efficiency and power density of the APM DC-DC converter,the topology and control strategy of the DC-DC converter with a two-stage structure are studied,then design a two-stage converter composed of three-level Boost(TLBoost)converter and half-bridge LLC resonant converter.The TL-Boost converter is used to convert a wide range of input voltage into a stable output voltage with small ripple,so as to better utilize the high efficiency advantage of the LLC resonant converter under specific input conditions.The control strategy of adopting phase-shift control and dynamically adjusting the conduction time of the switching does not increase the complexity of the control.The steadystate characteristics of the half-bridge LLC resonant converter are analyzed in detail,which provides theoretical basis for the parameter design of the resonant components.The designed converter has the advantages of wide input range,good stability high efficiency and high power density.Finally,the feasibility of the proposed converter is verified by experiments.