Research On The Voltage Equalizer Of Supercapacitors For Metro Energy Storage Systems

With the rapid development of the rail transportation today, how to reduce the subway’s energyloss and operating costs is especially important. The research on metro regenerative braking energyrecycling is of great significance to the development of rail transportation, the energy conservation aswell as the protection of environment. In metro regenerative braking energy recycling systems,supercapacitors(SCs) are widly used to store the regenerative braking energy. However, the voltageequalization of SCs in series is a key technical problem which limits the application of SC storagesystems. The equalizers of SCs become research hotspots. In this thesis, a SC voltage equalizationdevice used in1500V DC metro traction power grid is studied, and a novel voltage equalizationcircuit is proposed which is promised to achieve a high equalization precision. The equalizationdevice also has other auxiliary functions to guarantee the security and reliability of SCs.In metro regenerative braking energy recycling systems, SCs are required in large quantities.Thus, reasonable design is needed for capacity of SCs i.e. the number of monomers. Meanwhile, themanner of combination of SCs needs an optimized design. Based on the voltage, capacity, andcombination of SCs, different voltage equalizers are used between and within SC modules. A novelvoltage equalizer is proposed to fulfill the equalization between modules. The circuit is a two-stageconverter which is characterized by auto voltage equalization and a controlled current. It takesadvantages in circuit structure and equalization precision compared to traditional equalizers. Since theequalizer within modules has been provided by the SC module manufacturer, although it is notintegrated to the device, the equalizer within the module is researched individually. For the equalizerwithin modules, the management chip bq76PL536is used with a controller to achieve voltagesampling and equalization independently. This equalizer is a traditional one, i.e a kind of resistanceequalizer. The hardware platform is developed to evaluate the equalizer within modules. Finally,C8051F040is used as the controller of the voltage equalization device. The design of the device ispresented in detail. The prehensive functions of the device including the voltage equalization,sampling, protection, etc are introduced in detail. The equalizer has been tested and the experimentresults indicate that the equalizer has a good equalization capability and is with high precision.