Research On The Optimization Control Method For LCL-type Resonant Dual Active Bridge DC-DC Converters

Bidirectional DC-DC converters are widely used in distributed generations,electric vehicles,uninterruptible power supplies,etc.Nowadays DC microgrid technology develops rapidly,thus bidirectional DC-DC converters will play more central role in power conversion system.As a kind of bidirectional DC-DC converter,LCL-type resonant dual active bridge(LCL-DAB)DC-DC converter has broad application prospects in power conversion because of its high voltage gain,high power density,low backflow power and other characteristics.In this paper,LCL-DAB DC-DC converter is taken as the research object,and the optimization of backflow power,soft switching behavior and transient response characteristics are studied respectively.Firstly,this paper introduces the topology and energy transfer principle of the traditional dual active bridge DC-DC converter.On the basis of it,several common phase-shifting modulation methods of DC-DC converter are introduced,then the operation modes of the converter and the soft-switching realization of the IGBTs are analyzed with examples.Second,the input and output characteristics,the mathematical expressions of power transmission and voltage gain of the LCL-DAB DC-DC converter are derived.With different phase-shifting modulation methods,the influence of phase shifting variables on the voltage gain and the harmonic content of the inductance current for the converter are analyzed respectively.Third,in view of the backflow power and the transient response,the dynamic compensation based feedforward control against output/input disturbance for LCL-DAB DC-DC converter operated under no backflow power was proposed.The design regions under no backflow power for LCL-DAB DC-DC converter with TPS modulation scheme were analyzed,according which estimating an appropriate inner phase shift ratio can make the converter operate under no backflow in a wide range.On basis of it,a dynamic feedforward compensation unit was added in controlling progress,thus the system can achieve excellent transient response characteristic against disturbances.Moreover,in view of the backflow power and the soft-switching behavior,the seeking control method based perturbation and observation for LCL-DAB DC-DC converter operated under no backflow power and soft-switching was proposed.The design regions under no backflow power and soft-switching for LCL-DAB DC-DC converter with DPS modulation scheme were analyzed,according which the optimal modulation point can be found beside the approximate calculation point.By perturbation and observation method the optimal modulation point can be found,thus the backflow power can be eliminated in the input and the output supply.In addition,8 switches can achieve soft-switching when the voltage matches,and 6 switches can achieve soft-switching when the voltage does not match.Finally,the normalized mathematical model of the LCL-DAB DC-DC converter is established.According to the mathematical model,a simulation control system is built on the Matlab/Simulink platform,and the two optimized control methods proposed in this paper are initially verified.For further verification,an experimental platform with DSP and FPGA as the controller is designed,which proves the feasibility and effectiveness of the two optimed control methods.