| Considerable electricical energy was generated when subway trains regenerative braking. Absorption and utilization this part of the regenerative braking energy is a measure of improving the energy utilization ratio at the field of urban rail transit. The measure not only save energy but also protect the environment. With the accelerating construction of subway and the development of storage technology, the research on this aspect will become increasingly important.As a storing component with many good qualities, super capacitor developed very rapidly in recent years. The super capacitor energy storage system of absorbing station form is core content of this paper, which mainly include the following aspects:First of all, using dynamic analysis and braking characteristics curve method, the braking energy was quantitatively calculated. Based on this, the parameters such as electric capacity of the energy storage system and the series-parallel way of super capacitor storing array were designed.Considered the super capacitor series-parallel storing array, some voltage equilibrium measures were introduced. By the analysis of the functional requirements of the system, the structures and working mode of DC-DC converter was decided.Secondly, the mathematical model of super capacitor energy storage system was established, and its working principle was analyzed detailedly. In order to realize the control of bidirectional DC-DC converter and achieve the function requirements of SCESS to store energy and stable nets voltage, the two-ring control strategy of voltage and current was studyed and designed. Based on these, a new tri-loop control structure with a limited closed-loop of voltage and current was designed, when super capacitors' voltage was near the limits,the control strategy plays a role to control super-capacitors' voltage within limits and make use of its' capacity by the greatest degree. Meanwhile; the auxiliary inventer unit to use stored energy was designed. By analyzing the mathematical model of inverter, the linear relationship between super capacitor voltage and inverter output voltage was found, and the controller was designed.Finally, in order to verify the effectiveness of the system and control strategies, simulation system models were built by simulation software MATLAB/SIMULINK. The result of simulation shows that the control strategy can effectively and quickly control SCESS to work at energy storage and energy release mode, and SCESS can play a part in stabilizing voltage and storing energy. With regard to the auxiliary inverter unit of power utilization, its function was tested and verified by simulation. Combined with the simulation results,the influence factors of the energy recovery efficiency and utilization efficiency of system capacity were discussed,and the energy saving effect of the system was analyzed and evaluated. The research result demonstrates the correctness and validity of system design and control strategies. |
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