Design And Control Strategy Of Isolated Bidirectional Full-bridge DC-DC Converter Under Wide Range Input And Output Voltage

Power electronic transformers have attracted a lot of attention due to more compact and lighter compared with the same power transmission capability.As an important part of power electronic transformers,isolated bidirectional DC-DC converters have higher power density.It can be applied to the traction system and the auxiliary power supply system to realize the weight reduction of the locomotive,thereby improving the carrying capacity and increasing the transportation speed.In this paper,the isolated bidirectional full-bridge DC-DC converter is taken as the research object.The theoretical analysis,simulation and experimental verification methods are used to study the minimum current control algorithm,the wide range of input and output voltage range equivalent ratio real-time correction strategy and the duty-ratio phase-shift angle modulation strategy based on voltage level dwell time calculation.Firstly,the basic topology unit and structural characteristics of the DC-DC converter are compared and analyzed for the isolated bidirectional DC-DC converter.Simultaneously,the mathematical model of the switching function is established for the isolated bidirectional DC-DC converter.The mathematical relationship between the leakage inductor current RMS and the phase shift angle and the duty ratio of the primary and secondary port voltages is pushed,aiming at the minimum RMS of current effective value.We propose a controllable strategy for minimum current rms,which reduces the loss of the device by reducing the leakage inductor current RMS and improves the efficiency of the converter system.Secondly,based on the minimum current RMS control,the DC-DC converter with constant input-output voltage ratio is analyzed.The influence of the equivalent ratio of the circuit on the current RMS is analyzed to optimize the hardware parameters and control parameters of the converter.For the case where the equivalent ratio of the DC-DC converter operating in the wide input-output voltage range is not constant.this paper analyzes the influence of the k~*in the controller and the converter equivalent ratio k mismatch on the system control results.A real-time correction control strategy is proposed for the equivalent transformation ratio k~*in the controller,which solves the problem of the efficiency reduction or even the system out of control caused by the converter's equivalent ratio mismatch.Based on the minimum current RMS control and the equivalent ratio real-time correction control strategy,the paper continues to study the modulation strategy of the isolated bidirectional full-bridge DC-DC converter:Firstly,a duty cycle-phase shift angle modulation strategy based on SPWM principle is proposed.The paper introduces the implementation principle of duty cycle modulation and phase shift angle modulation under the modulation strategy,then deduces the constraint range of phase shifting ability under the modulation strategy.In order to solve this constraint problem,a"duty-shift phase modulation strategy based on level action time calculation"is proposed by referring to the implementation principle of SVPWM modulation strategy.Compared with the SPWM-based duty cycle-phase shift angle modulation strategy,the proposed modulation strategy can achieve full angular range phase shift under any duty cycle condition,overcoming the defect that the phase shifting capability is constrained by the duty cycle size.Simultaneously,this strategy reduces the required input clock frequency and improves modulation accuracy under the condition that the same data width and the drive signal of the same frequency is modulated and output.Finally,based on the theoretical analysis,the simulation model of the isolated bidirectional full-bridge DC-DC converter is built with the MATLAB/Simulink simulation tool,the simulation results are consistent with the theoretical analysis.Based on the results of theoretical analysis and simulation verification,an isolated bidirectional full-bridge DC-DC experimental prototype with a working frequency of 25 kHz and 15KVA/600V-110V is built.The core of the control algorithm is designed based on FPGA and Verilog HDL hardware description language.the proposed current RMS minimum control strategy,the equivalent ratio real-time correction control strategy and the modulation strategy are verified by experiments.