Energy Saving Technologies For Power Supply Systems Of Urban Rail Transit Vehicles

The rising awareness of environment protection has boosted unprecedented development of urban rail transit as a green option for travel in China,but many existing systems can hardly live up to the concept of building green transport.This is particularly true today as the advancement in electricity,electronics and energy storage,as well as the wide application of energy feedback system to regenerative braking further complicate the composition of the power supply system as well as the power relations between the train and the ground.Given the lackluster models available for the integrated description of the power supply system onboard and on the ground,overcapacity becomes a regular occurrence amid the energy upgrade of existing equipment and amid the capacity setting for energy feedback,piling up the financial burdens for the stakeholders concerned.With a focus on the power supply and the energy-saving systems of urban rail transit,the paper studies the topological structure of the low-voltage DC power supply system onboard,the energy management methods of the storage battery system onboard as well as the configuration of the energy-saving system on the ground.The efforts aim to apply EMMS to the integrated simulation of power supply systems both onboard and on the ground,so as to analyze the energy-saving configurations of the two and improve the efficiency of the overall power system.The highlights of the paper are as follows:The paper proposes lithium titanate battery set as an alternative to the traditional option installed in the low-voltage power supply system onboard.As energy is absorbed and compensated amid dynamic charging and discharging,the new approach conducts dynamic management of charging and discharging using bi-directional chargers.The improved use of energy helps cut energy consumption amid train operation.In line with the characteristics of lithium titanate battery and the needs for dynamic charging and discharging,the paper takes the balance of energy amid charging and discharging,and the maximum efficiency of energy conversion as the goal of energy management.For that to happen,it puts forward the control models for the charging and discharging of the battery set,complemented by two topological schemes for bidirectional chargers,which leads to the corresponding EMMS models for the low-voltage DC power supply systems proposed.With the help of the models built,the paper – on one hand – strives to optimize the control strategies of the chargers where the Modified Greedy Algorithm well suited for the charging/discharging management of the lithium titanate battery helps reduce potential errors occurred in the results ranking.On the other hand,the paper works to improve the simulation of the battery,in which case the introduction of entropy heat coefficient leads to the building of an equivalent model for the battery compatible to the EMMS of the overall system.Then,the multi-dynamic parameters obtained via PI observer are applied to optimize the parameters of the equivalent model.A better simulation of the voltage and the temperature of the battery set elevates the model precisions.Afterwards,in the environment of Simulink,an EMMS simulation model for the low-voltage DC power supply system is created where the energy saving performance is simulated and compared using the data collected amid the operation of the No.1 Metro Line in Changsha（Hunan province,China）.Then the EMMS depictions of the power supply system onboard,that on the ground and the energy feedback system on the ground are introduced to the Simulink environment.In line with the corresponding speed curves,the paper works to reflect the integration of multiple trains with multiple power supply systems involved,and evaluates the energy saving performance of the battery onboard and the energy feedback system on the ground.The linear programming model for the battery set and the energy feedback system helps weigh the input and the outcomes,and the ranking of the results visualizes the corresponding configurations for different scenarios.