Control Strategy For Dual Active Bridge Bidirectional DC/DC Converter

Due to solar energy is easily affected by the weather and the environment, it needs storage device in the photovoltaic energy storage system. And energy transmission between storage device and DC bus is required bidirectional DC/DC converter. Therefore, the study of bidirectional DC/DC converter has extremely important value and significance. Taking current stress, backflow power and soft switching range as the optimization goal, this thesis is dedicated to studying control strategy of the dual active bridge(DAB) topology of bidirectional DC/DC converter. Then optimization control strategy is chosen based on the optimization goal in order to optimize system performance and improve efficiency of DAB converter.Because of nonlinear character, the stability of DAB converter is discussed by Lyapunov function method. And bidirectional energy transmission of DAB converter is discussed under phase shift control. Theoretically simple averaged model and small-signal model are presented. The soft switching range and backflow power of DAB converter under traditional phase shift control is discussed. The simulation analysis shows that the converter has large proportion backflow power and the switches suffer high current stress.A new method is presented which can be convenient to analyze soft switching range under different voltage ratios. And it is used binary number represented for soft switching realization of two power switches on the same bridge arm. In view of the problem of backflow power under traditional phase shift control, by introducing phase shift control in inner unit bridge, phase shift plus one side modulation and phase shift plus two sides modulation of DAB conveter are discussed. It is pointed out that two new control modes can effectively reduce backflow power and peak inductor current. Meanwhile, it can effectively expand soft switching range and improve the efficiency of the converter.Then two optimal control strategies based on peak inductor current and backflow power are analyzed. It is given comparative analysis from peak current, backflow power and soft switching range three aspects under one given transmission power. The simulation analysis shows that the DAB converter’s performance is changed with different optimization goal. Namely, all performance indices of DAB converter can’t be achieved optimal at the same time when it is used one optimal control strategy.An experimental prototype of DAB bidirectional DC/DC converter is built. Under one given transmission power, it is used phase shift plus one side modulation and phase shift plus two sides modulation compared with traditional phase shift control. The experimental results show that peak inductor current is effectively reduced, also the proportion of backflow power is significantly decreased. What’s more, it is increased two power devices which can achieve ZVS(Zero Voltage Switching).