Research On The Control Technology For Soft Switch DC-Source

The improvement of living standard in modern society and the increasing progress of science and technology have made the demand for switching power supply performance higher and higher.In order to meet the requirements of switching power supply,The higher switching frequency,the smaller power supply size,the more precise digital control are the future development of switching power supply.However,The higher switching frequency also brings some problems which need to be solved.From the past experience,the switching frequency is proportional to the switching loss of the system and inversely proportional to the conversion efficiency of the system.The emergence of soft-switching technology can solve a series of problems caused by increased switching frequency,and it is also widely used in engineering.In this paper,firstly analyze the topology of a variety of phase-shifted full-bridge of soft-switching DC-DC converters,summarize the advantages and disadvantages of each topology,and then select the main topology of lagging-leg series diodes as the research object,and specific analysis for the structure.Since the secondary rectifier diode exists the parasitic capacitance,the secondary voltage waveform is easy to oscillate.After analyzing the oscillation reason,In this paper,a method that can suppress the secondary oscillation by adding auxiliary circuit.Aiming at the phenomenon that the converter is not effective in leading the bridge arm switch at light load,an improved measure to adding the auxiliary current source in the lead arm is proposed.The principle of designing the auxiliary circuit and analyzing the range is proposed and verified by simulation.According to the small signal analysis method,the mathematical model of the main circuit is established.The control structure of the voltage inner loop and the current outer loop are adopted and the specific design process is given.Because the traditional PI controller does not have the function of on-line tuning,at the same time,the ability to deal with the complex conditions of load switching is poor,and there are some shortcomings such as the delay of digital control,so there is a delay of one sampling period in the control action.The control strategy of predictive fuzzy PI control which combines predictive control technology and fuzzy PI control is presented and the design method is given.The two control strategies of the traditional control and the predictive fuzzy PI control are respectively simulated.The simulation results show that the predictive fuzzy PI control has a better coping ability to switch the complicated operating conditions and better meet the system requirements.Finally,the control system based on STM32F407 is designed.The simulation waveforms are verified by the built experimental platform,which proves the consistency between theory and practice.