Double Closed Loop Control Strategy Of Bidirectional DC/DC Converter With Phase Shifting Full-Bridge

To solve the problem of global warming, environmental pollution and meet the requirement of high-speed economic development, the research on renewable energy is urgent. Wind power and photovoltaic power are intermittent and random which need flow battery to work as energy storage device to buffer energy, reduce the randomness and improve the stability of the power. Battery needs the converter to work as the charging and discharging interface when it is applied to the micro grid.Bidirectional inverter (DC/AC) and bidirectional DC converter (DC/DC) act respectively as flow battery charging and discharging interface of AC and DC micro grid. The theory about them has been developed rapidly, while the application study is still very limited. The application field, system modeling and the control strategy of the converter is the key of the application study. The paper focuses on the modeling and the control strategy.First of all, the paper compares the characters and application of the common battery, and chooses the flow battery as the energy storage device. Then the paper analyzes the structure, working principle, charging and discharging mode of flow battery and establishes the equivalent circuit model. According to the characters of battery, the charging and discharging control strategy of constant current first and then constant voltage is confirmed.Secondly, the paper introduces several typical bidirectional dc converters, and analyzes their working principle, characters and applications. After that, we draw the conclusion that the phase-shift full bridge bidirectional dc converter is applicable to the charging and discharging interface circuit of flow battery.Thirdly, the paper divides clearly the phase-shift full bridge bidirectional dc converter into six modality, analyzes in depth the transient working process and calculates the relationship among current, voltage, power and the circuit parameters of the six modality quantitatively. Then the small signal model is established in acceptable error.Finally, according to the models of the battery, the converter and the adoptive control strategy above, the paper designs the double closed_loop controller. Moreover, the control system is simulated in MATLAB/Simulink and simulation results are given.The simulation results show that it’s practicable to use the bidirectional dc converter to accomplish charging and discharging control of the battery. The controller applied to the simplified model is also suitable for the equivalent circuit model. The system has good robustness.