| A large amount of regenerative braking energy will be generated during the operation of urban rail transit.In recent years,major metro companies have invested in energy feeding devices to invert the regenerative energy back to the medium voltage AC power grid for secondary utilization and remarkable energy-saving effect.At the same time,energy storage and power supply devices are also used in this occasion.When the train is braking,the excess energy will be stored in lithium titanate battery or other energy storage media,and will be released to the DC power grid when the train starts or loads.Compared with the energy feeding device,the energy storage and power supply device can not only use the regenerative braking energy,but also have a good supporting effect on the DC power grid.It is one of the development directions of the utilization of regenerative energy in the future.In this paper,the urban rail energy storage and power supply device based on lithium titanate battery is studied and a complete set of device is developed.The main contents are as follows:Topology selection and modeling analysis of energy storage converter.The switching state and current flow path in the full range of duty cycle of flying capacitor three-level bidirectional DC / DC main circuit topology in step-down and boost mode are carefully analyzed,and the voltage relations between high voltage side and low voltage side are derived.Then the main device parameters of the main circuit are analyzed and calculated,and the parameters of high voltage bus capacitance,flying capacitance and filter inductance of lithium titanate battery energy storage and power supply device are calculated.At the same time,the calculation parameters are simulated to verify the rationality of the calculation parameters.Control strategy of energy storage converter.The buck mode and boost mode are modeled by the state space average method,and their open-loop characteristics are analyzed.The double closed-loop control mode based on inductance current and catenary voltage is adopted.The analysis results show that the control mode meets the control requirements.An engineering prototype of lithium titanate battery energy storage and power supply device is designed.The charge discharge performance,dynamic response performance and efficiency of the energy storage converter are tested.The test results:Efficiency>98%;The temperature of power module radiator is stable at 72 ℃;Full power response time427.5ms;Noise 78.6d B.Shows that the DC-DC converter with flying capacitor three-level topology has excellent performance,high efficiency and fast dynamic response.At the same time,the energy storage and power supply device based on lithium titanate battery can meet the application occasions of high-power charge and discharge in subway. |
