Research On Dual Active Bridge Bidirectional DC-DC Converter

With the development of the economy and productivity, the consumption of traditional energy such as coal, oil and natural gas grows, efficient and clean photovoltaic, wind power and other new energy power generation technologies are getting more and more attention. But these new energy generation technologies are affected by the natural conditions, have the characteristics of instability. They should use energy storage devices to eliminate the fluctuation of system parameter. Bidirectional DC-DC converter is mainly used in the solar cell array, uninterrupted power supply system, fuel cell power system, port hybrid power supply system and DC power amplifier, it has bidirectional power transfer capability.In this paper, dual active bridge(DAB) bidirectional DC-DC converter as the research object is a kind of bidirectional DC-DC converter usually used in high-power application. DAB bidirectional DC-DC converter has the advantages of high power density, zero-voltage switching(ZVS), bidirectional transfer power, high efficiency, symmetric structure and simple control etc.Firstly, This paper introduces three kinds of common control methods of DAB bidirectional DC-DC converter(phase shift control, single PWM plus phase-shift control, dual PWM plus phase-shift control), and analyzes their operation principles and operating characteristics respectively.Secondly, in view of the DAB bidirectional DC-DC converter has the problem of DC offset under phase shift control, this paper analyses it’s reasons, and proposes a compensation strategy of dead time to eliminate the DC offset.Then, the DAB bidirectional DC-DC converter will lose the ability of zero voltage switch using the phase-shifting control at light loads, but it is suitable for operation using dual PWM plus phase-shift control under light loads, and when the loads increases, the inductor current is increasing using dual PWM plus phase-shift control even beyond using single PWM plus phase-shift control, thus a multiple model control method is put forward. At light loads, the dual PWM plus phase-shift control is used, with the increase of loads, it is switched automatically to single PWM plus phase-shift control, if the loads continue to increase, the converter will be naturally switched to the phase shift control at the 90° phase-shift angle. Moreover an optimized PWM plus phase-shift control method is applied to the multiple model control strategy, it can achieve zero voltage switching and reduce the RMS of inductive current, and improve the efficiency of the converter.Finally, the proposed two strategies above have been simulated by building a simulation model built in Matlab/Simulink environment. Simulation results show that the compensation strategy of dead time can solve the problem of the DC offset, and the multiple model control strategy makes the DAB bidirectional DC- DC converter zero voltage switching and higher efficiency in the full rang of load.