Variable Parameter Control Method Of Wide Voltage Range Bi-directional Active Isolation DC-DC Converter

With the development and application of power electronic devices,power electronics technology has been innovated constantly.Power electronic converters are required to have a series of characteristics in rail transit,aerospace,military equipment,hybrid energy storage technology,new energy generation and other fields.These characteristics include wide voltage range adaptability,high voltage conversion ratio,high efficiency,bi-directional power transmission ability.In this paper,the isolated two-side half-bridge three-level DC-DC converter topology is adopted.Under the condition of wide range of voltage variation.On the basis of two-sided three-level control,a variable parameter control scheme is proposed,which makes the effective value of leakage inductance current is optimized in real time.By this method,light load efficiency of converter can be improved and current stress of switches can be reduced.In a wide range of voltage variations,the isolated DC-DC converters are divided into two categories:equivalent buck type?k?1?and equivalent boost type?k>1?.First,the working principle,power characteristics and soft-switching characteristics of equivalent buck DC-DC converter are analyzed.Under the premise of same transmission power and the control objective for minimum effective value of leakage inductance current,the duty cycle expression of the optimal control of the buck type DC-DC converter is obtained.The converter can realize soft switching in full power range,and the effective value of leakage inductance current can be reduced to zero on no load condition.Secondly,the working principle,power characteristic,soft switching characteristic and minimum effective value of leakage inductance current of equivalent boost DC-DC converter are analyzed.The working characteristics of k?1 and k>1 converters are consistent with the optimization trend.With the increase of transmission power,the optimized working waveform of the converter changes from bilateral three-level to unilateral three-level and then to phase shift in both two kinds of converter.Under the wide voltage range,the optimal duty cycle expressions of k?1 and k>1converters are unified.By judging the k value,the optimal duty cycle expression of k?1 is the only thing needed in the controller,which simplifies the design of the controller greatly.In view of the problem that the traditional fixed parameter control scheme cannot adapt to the wide range of voltage variation and the converter working waveform is not matched,a variable parameter control scheme is proposed.The input voltage is introduced into the control loop,and the equivalent voltage variable ratio k is calculated in real time.The three control variables D?,D₁,D₂ of the two-sided three-level converter are updated so that the optimal waveform is always matched with the change of input voltage.The feasibility of the variable parameter control scheme is verified by simulation on Matlab/Simulink.Finally,based on the FPGA chip and Verilog HDL language,the controller software is designed.An experimental platform with input voltage of 60²00V,output voltage of 110V and transmission power of 400W is designed.Under the wide input voltage range,the efficiency and the effective value of leakage inductance current of the traditional fixed parameter control scheme and variable parameter control scheme are compared and analyzed.The experimental results show that the efficiency of variable parameter control is more than90%at light load in the wide voltage range,which verifies the effectiveness of the variable parameter control scheme.