| The energy problem is the bottleneck of current social development,and how to achieve efficient use of electrical energy through new technological means is the current research focus.In order to solve this problem,clean power sources such as photovoltaics and tides have received widespread attention,due to the influence of natural factors,their output voltage has the characteristics of discontinuousness,poor stability,and low utilization.Therefore,it is necessary to study the DC/DC converter.LLC resonant converter is a widely used DC/DC converter,at present,the main problems of the wide input range LLC resonant converter are:complex topology,too wide frequency range,and insufficient input range.In addition,compared with the traditional analog control technology,the digital control technology has the characteristics of high flexibility,good accuracy,strong controllability,and diverse and efficient control algorithms.Based on the above reasons,this paper proposes a new LLC topology structure suitable for a wide input voltage range,using frequency conversion control,which can adjust the circuit structure according to different input voltage ranges and optimize system performance.The main work of the paper is as follows:(1)The topology and working principle of the new LLC converter are elaborated in detail.The circuit includes a full-bridge LLC sub-topology and a three-level LLC sub-topology.The working principles and structural switching methods of these two circuits are analyzed separately.The fundamental wave analysis method is used to mathematically model the topology circuit,and its gain characteristics and working area are deduced.The new LLC topology is theoretically proved to be suitable for wide input voltage applications.(2)Converter main circuit design.Select the MOSFET as the main power switching device,and select the single-phase bridge full-control rectifier circuit for the secondary side rectification;Calculate and analyze the voltage and current stress and parasitic parameters of the main switching device,and select the appropriate high-frequency switching tube;Calculate the charging and discharging time and voltage stress of the resonant capacitor during the working cycle,and choose the capacitance of the resonant capacitor reasonably;Investigate the design and manufacturing methods of high-frequency transformers.Integrating the resonant inductor into the transformer effectively reduces the volume of the converter and increases the power density.At the same time,the parasitic parameters are effectively reduced by optimizing the winding process of the transformer.Independent design of driving circuit based on pulse isolation transformer to solve the problems of driving waveform clutter interference and driving delay.(3)Design the control system based on DSPF28335,analyze the on-chip resources of F28335 in detail,describe the design details of clock initialization,PWM initialization,ADC initialization,etc,and design the PI control system process and software control framework.(4)Circuit simulation and experiment.Based on the results of theoretical analysis,a simulation circuit was built using the PSIM circuit simulation software to simulate the working characteristics of the circuit in the full input range,and stable control of the output voltage was achieved through analog frequency conversion control.Finally,based on the theoretical analysis and simulation results,a 500W experimental prototype is built.It is found through experiments that the output is 48V/10.4A within the input voltage range of 100V-600V,and the full load efficiency can reach up to 92%.It can be used under wide input conditions It realizes the zero voltage conduction of the switching device and the zero current shutdown of the rectifier diode.Through the frequency conversion control,the output voltage can be stably controlled,with high control accuracy and good dynamic performance. |
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