Research On Mixed Power Source Of Hybrid Electric Railway Vehicles

With the rapid process of urbanization, people’s high demand for the urban mass transit (UMT) is promoted increasingly, since UMT plays a positive role in optimizing the urban spacial infrastructure, relieving urban traffic jams and protecting the environment. However, the catenary constructed for power supply in traditional UMT is easy to cause accidents and affects the city appearance. Also due to the dependence on absorbing residual energy of the adjacent vehicle, the way using regenerative braking energy at present time has low efficiency of energy usage. In addition the redundant energy consumes on the braking resistance, which increases the burden of the cooling system. Therefore, the mixed power source for UMT proposed in this study, which can reduce the scale of the catenary along the track and solve the problem for braking energy usage with low efficiency, has great significance for the development of the urban transport and the urban planning.Battery and super capacitor are the major components of the mixed power source in this study. As a traditional energy storage source, battery has many advantages, such as high specific energy, stable output voltage and so on, but its output power is limited in a small range. On the other hand, super capacitor, which has high power density, rapid charge and discharge, and long cycle life, takes a rapid development in recent years. However, in comparison with battery, super capacitor has lower specific energy. This paper presents a primary investigation on the power source technology of the hybrid electric train. According to the practical demand for the power source of the hybrid electric train, this paper envisages a reasonable structure of the power source and proposes a power assignment strategy for energy management based on the research for the charge and discharge performance of battery and super capacitor. Then a research foundation is constructed for the hybrid electric train using the model of catenary-battery-super capacitor as power supply. The main work of this paper includes:(1) According to the operating characteristics of the train, the experimental method is presented for lithium-iron-phosphate battery, and the complete measure process is designed for different test conditions. Based on the experiments, the characteristics of lithium-iron-phosphate batteries, such as the voltage, current and capacity, are studied with different charge-discharge rate in different periods. Moreover the parameters of selected batteries for the hybrid electric train are verified then, and the experiment data provides the basis for the charge-discharge strategy of battery.(2) According to the charge-discharge characteristics of super capacitor, the charge-discharge experiments for super capacitors are carried out with different currents and the following variables: voltage, current, capacity and internal resistance are measured in real time. Based on the experiments, the super capacitor characteristics of voltage, current and energy are analyzed with different charge-discharge currents. The parameters of selected super capacitors for the hybrid electric train are verified then, and the experiment data provides the basis for the charge-discharge strategy of super capacitor.(3) According to the performance of the power source and the operating demand of the train, the structure of the mixed power source system is designed and the power assignment strategy for energy management is developed. With the guidance of this strategy, different work modes of the system are analyzed to satisfy different work conditions. Furthermore the structure and work principle of DC/DC, which is the key component to control energy flow, is analyzed then, and a double closed control loop for the converter is designed to guarantee the stability of the input and output energy.(4) According to the performance demand of the train and parameters of the power source, the serial and parallel structure of the power source is configured from the perspective of energy and power consumption, In the frame of Matlab/Simulink, the simulation model of the mixed power source is built with four main modules: energy management module, bi-directional DC/DC converter module, battery module and super capacitor module. Then the performance of the controller and the basic functions of the power source are tested by switching power demands. Moreover, based on the simulation analysis with different typical work conditions, including climbing, endurance, launching-acceleration-braking and braking feedback, the validity of the energy management strategy and the feasibility of the mixed power source are verified.