Research On Pulsed Load Two-Stage DC-DC Converter

In radar,transmitter and other power supply systems,the load is pulsed characteristic,high peak to average power ratio.In the traditional single-stage DC converter structure,the load end is combined with the large-capacity energy storage capacitor to provide peak power,which is large in volume and affects the power density of the system.On the other hand,the duty cycle of the load in electronic countermeasures and other applications is usually large,which puts forward higher requirements for the dynamic response of the DC converter to meet the performance of the whole machine.To solve the above problems,this paper firstly analyzes the transient process of pulsed power and the factors causing voltage fluctuation of energy storage capacitors,and compares the demands of different voltage levels on energy storage capacitors.A two-stage pulsed load DC conversion scheme is proposed,in which the energy storage capacitor is placed in the middle high voltage bus to reduce the capacity demand of the energy storage capacitor.At the same time,in order to meet the requirements of the fast dynamic response of the back-stage converter,the performance of different topologies are compared and analyzed from parasitic parameters,system loop bandwidth,filter inductance and other factors,and LLC scheme of fixed-frequency modulation is selected.In this paper,a three-level Buck converter(TL-Buck)with smaller filter inductance and higher loop bandwidth is selected as the front stage converter.Its working mode and circuit characteristics are analyzed in detail,and the circuit parameter design and loss analysis are given.Aiming at the problem that the voltage of TL(Three Level)-Buck flying capacitor cannot be stabilized at Vin/2 when the loop is open,which leads to the increase of the ripple of inductance current and capacitor voltage and limits the loop bandwidth,a double closed-loop control strategy was proposed to decouple the output voltage from the flying capacitor voltage.Aiming at the factor of inductance current change rate that affects the dynamic recovery time of output voltage in the process of pulsed power balance,a transient controller based on duty ratio extended mode is used in this work,and a soft start strategy is proposed to optimize the voltage stress problem of TL-Buck switch tube.DCX(DC Transformer)-LLC converter is selected in the last stage of this paper,and its working mode and circuit characteristics are analyzed.The advantages of DCX-LLC over closed-loop control LLC in dynamic response,efficiency and power density are analyzed.According to the characteristics of its K and Q values,the optimized main circuit parameters suitable for the application in this paper are given.The magnetic components are designed and the losses are analyzed.Finally,a simulation platform based on Simulink and a hardware experiment platform with an average power of 600 W are built.Aiming at the above research content,the correctness of the research theory is verified by simulation and experiment.