| In recent years,the scale of urban rail transit in China has grown rapidly.By the end of2020,metros have been opened in 44 cities,and the total mileage has reached 7715.31 km.Due to the frequent start-up and stop of metro,the traction energy consumption is high,how to reduce the power demand of metro on urban power grid,and realize "Energy Saving,Low Carbon,Green and Environmental Protection" travel of urban rail transit,which has become an urgent problem to be solved in urban rail transit system.The application of renewable energy is an important way to reduce the energy consumption of urban rail transit system and improve the energy efficiency of the system,therefore,the energy scheme of wind and photovoltaic combined power supply is proposed.In order to alleviate the impact of the instability of wind and light energy on the traction network,a hybrid energy storage system with super capacitor and battery is used to stabilize the wind and solar fluctuations.The empirical mode decomposition algorithm combined with Hilbert transform is used to get the power signals with different frequencies.The high frequency signal with large frequency variation is distributed to the super capacitor with fast response speed,and the low frequency signal with high energy is distributed to the battery with large energy storage capacity.By installing a hybrid energy storage device in the traction substation along the metro line,the power fluctuation caused by wind and solar power generation is suppressed,but it increases the cost of construction and maintenance of traction power supply system,and the battery has a short life and needs to be replaced continuously during use,therefore,it is necessary to configure the rated power and capacity of the hybrid energy storage device according to the actual situation of metro traction load and the state of charge constraints of the energy storage device.Through the characteristics of particle swarm optimization algorithm to find the optimal solution among the particles,two kinds of energy management strategies are established respectively aiming at the construction and maintenance cost of energy storage system and the life loss coefficient of battery,so as to realize the reasonable configuring of electric energy.Because the traction current of DC catenary fluctuates obviously,so it is necessary to predict the traction current in the power supply section of the traction substation in order to provide a reference for the power dispatching of the hybrid energy storage system.After the influencing factors of urban rail transit traction load have been determined,and the autoregressive integrated moving average algorithm is selected in Eviews software to predict the traction current data,Through the test and optimization of data and model,finally get the prediction results.Compared with Fourier algorithm,it can be concluded that the autoregressive integrated moving average algorithm has higher prediction accuracy.In the process of power dispatching and using,in order to prevent the super capacitor from overdischarging,the discharge ratio of super capacitor is adjusted by fuzzy control,combined with the predicted value of traction current,the discharge ratio of super capacitor in different state of charge is obtained.Aiming at the problem of high traction energy consumption of urban rail transit,this paper studied from three aspects of source,storage and load respectively,and obtained the capacity and power configuration scheme and energy management strategy of hybrid energy storage system composed of super capacitor and battery,which provided reference basis for realizing energy saving and consumption reduction of urban rail transit. |
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