Optimal Modulation And Parallel Current Sharing Control Of Dual Active Full-Bridge DC-DC Converter

With the rapid development of distributed energy,microgrid technology has become an effective means to dissipate distributed power.Storage batteries such as batteries and supercontainers need to be equipped with bidirectional DC-DC converters to achieve bidirectional transmission of energy when accessing the microgrid.The dual active full-bridge(DAB)has many advantages such as electrical isolation,high-ratio buck-boost,easy soft-switching control,and multiple modularization through series-parallel combination.The solution is widely used in large and medium power applications such as distributed generation.Because the DAB converter has multi-variable control and system nonlinearity,the efficiency needs to be improved.In addition,in the high-power case,the modular parallel connection of the converter also needs to achieve the power balance of each module.For this reason,this paper mainly carries out the optimization of the converter.Modulation strategy research and modular parallel power balance strategy research.In this paper,the traditional single phase shift,extend phase shift and double phase shift transmission power,return power,current stress and soft switching characteristics of DAB converter are compared and analyzed.The dual phase shift control has the widest power transmission range and the strongest flexibility.In order to reduce the power loss of the DAB converter,considering the different transmission power and input-output voltage regulation ratio in the global range,a dual phase-shift current stress optimization control strategy is proposed,and the double-phase-shift control is used to control the inductor current of all operating modes.The mathematical relationship between stress and voltage regulation ratio,transmission power,and phase shift angle.On this basis,the phase-shift angle conditions of the converters operating in the optimal current stress state are derived.The global optimization of the converters is ensured by segmentally optimizing the internal phase shift angles of the two bridges and the phase shift angle between the bridges.The current stress is optimal within the range.Further considering the modular parallel operation of the DAB converter in high-power applications,the power balance problem of the independent input parallel output DAB converter is taken as the research object,in order to ensure that the parameters of the system DAB modules are not matched or the input voltage amplitudes are not equal.The automatic balancing of transmission power can be realized,and a current-free current sharing control strategy based on dual phase shift control is proposed.The method realizes the automatic estimation of the system parameters through the disturbance,and completes the step-by-step automatic power balance control of the parallel output modules of each phase.Compared with the traditional single phase shift current sharing control method,the operating efficiency of the converter is improved,the circuit is simplified,and the system cost is reduced.Finally,a 5kW DAB converter experimental prototype was built,and the proposed current stress optimization control strategy and current-free sensor current sharing control strategy were verified.Steady-state and transient experimental results show that the current stress optimization control strategy improves the efficiency of the converter from light load to full power range.The current-free current sharing control strategy can effectively realize the inductor current and output when the system module parameters are not matched.The current is balanced and the dynamic performance is excellent.