Research And Manufacture Of Three-Level Modular Super Capacitor Charger

Urban rail transit system is an important tool to ease the traffic problems in modern cities. Modern urban rail transit system generally adopts the power supply mode of overhead contact net. Because overhead contact net has the problem of high cost and affecting the civic landscape, people focus on the new way of urban rail transit power supply. Super capacitor has the advantages of high power density, fast charge and discharge, and long life, so the power supply based on super capacitor has a broad application prospect in urban rail transit system. In the urban rail super capacitor power supply system, power charger is the necessary equipment. This paper focused on the super capacitor charger from the following aspects:The design of the main topology. Based on the super capacitor charger of urban rail with high efficiency and high power charging requirements, this paper selected the modular intelligent of three-level buck converter as the main topology of super capacitor charger. By analyzing the operating principle and characteristics of the three-level Buck converter, this paper concluded that it could reduce the inductance, reduce the noise and improve the switching frequency compared with the two-level Buck converter. The structure of modular circuit compared to the single module structure could increase the redundancy of the system and reduce the current ripple in the circuit. According to the requirement of the charger designed index, the main circuit parameters were calculated and designed.The design of control strategy. According to the charging characteristics of the super capacitor, the charging method of constant current and limiting voltage was adopted. According to the voltage regulation characteristics of the flying capacitor in the converter, a voltage regulator control strategy based on the flying capacitor voltage regulator was designed. In the modular structure unit, the control strategy of the wrong phase was added to each module. The final control strategy was made up of constant current, limiting voltage, regulating voltage of flying capacitor and phase-shifting of modular structure unit. Based on the control strategy, this paper designed the structure of the controller.Simulation verification. The model of the designed modular three-level buck converter had been built to make simulation analysis in Matlab. In the condition of the maximum voltage and current fluctuations, the designed main circuit parameters could meet the designed requirements of the inductor current and the capacitor voltage fluctuation. Through the analysis of triple modular circuit simulation, the results verified the characteristics of the designed control strategy was correct and the main circuit current ripple reduced.Experimental verification. Based on the existing laboratory conditions and equipment, the experimental verification had been made with Infineon microcontroller hardware control and MFC monitoring. The experimental platform of small power three-level charger realized the function of the designed three-level charger.