Application Of Bidirectional DC/DC Converter In The Electric Vehicle

With the development of transportation, private cars also gradually increase, but the traditional fuel automobile was largely dependent on oil, the increment of cars not only caused the incremental consumption of fuel energy, but also brought natural environment pollution. With the requirement for saving energy and protecting environment, the electric car has been rapid development in recent decades. Because the battery power is low than the existing shortcomings and limited lifetime, electric vehicle loading super capacitor can prolong the service life of the accumulator and can absorb the braking energy, and can save energy. Bidirectional DC/DC converter, as an important unit of electric vehicle energy treatment, can realize bidirectional flow of energy, and can control the charge or discharge of the energy storage, plays a decisive role in driving performance of electric vehicles. In this paper with the super capacitor as the performance requirements of electric vehicle auxiliary power system of bidirectional DC/DC converter, two interleaved bidirectional half bridge DC/DC converter was selected as the topology. And different control strategies were setting up for the control target, in order to improve the static and dynamic performance of the converter.Firstly, the advantages and disadvantages of the bidirectional DC/DC converter were discussed, and the bi-directional half bridge DC/DC converter that the voltage stress is relatively low was selected. In order to meet the requirements of high current electric vehicles and to reduce the output ripple of the converter. The two bidirectional half bridge DC/DC converters in parallel, consist of intersecting fault type half bridge bidirectional DC/DC converter. The two intersecting fault type half bridge bidirectional DC/DC converter’s working principle and circuit parameters design were described and the waveform of the converter in different operation modes was drew.Secondly, according to the requirements of the electric vehicles of different running state of DC/DC converter, a control target was cleared, the voltage and current double closed-loop control strategy was adopted, and the small signal model of converter working in Buck mode and boost mode was derived through the state space average method. The corresponding pi controller was set up, the system Bode diagram before and after compensation was drew out, and the stability of compensated system was verified. Because the bidirectional DC/DC converter in the electric vehicle is a nonlinear system and the input voltage range is wide, the traditional fixed parameter PI control is difficult to achieve the desired effect. This paper, combined with the advantages of fuzzy control and PI control, uses the fuzzy PI control of voltage outer loop and the control strategy of the traditional PI control of current inner loop to improve the response speed and system robustness. This paper sets up fuzzy PI controller and the domain membership function of input and output controller fuzzy control rules to determine the fuzzy method, and uses MATLAB to draw the fuzzy controller output Delta KI, Delta KP fuzzy control drawing.Finally, in order to realize the control strategy of bidirectional DC/DC converter, TMS320F2812 was used as the processor. The analog PI controller was discretized, and the main program flow was set up. In the MATLAB/SIMULINK, according to different control strategies, the simulation model of the converter was built, the design of converter and its control strategy is validated, and the simulation results were compared and analyzed. The results show that the fuzzy PI control can better solve the problem of nonlinear system, improve the robustness of the system.