Optimized Control Strategy Of Supercapacitor Based Energy Storage System Considering The Influence Of Wide Voltage Operation Range

As a novel method for regenerative braking energy recovery, supercapacitor based energy storage system (ESS) which is used for urban rail transit, can reduce the traction consumption and mechanic abrasion effectively. In application, charging and discharging power and transient response of ESS could be affected by the variation of substation open-circuit voltage and ESS steady operation voltage. This thesis will analyze the influence of factors mentioned above, and propose improved control methods for solving these problems.Firstly, the structure of urban rail transit system with supercapacitor based ESS will be introduced. And then, according to the output characterization of substation rectifier and supercapacitor based ESS, a large signal model of subway power supply system is proposed. Small signal models of supercapacitor based ESS in charging and discharging states are proposed, which are considering the characterization of supercapacitor and power supply system, by using state space average method.Then, according to output characteristic model of substation rectifier and energy storage device, output power ratio in different discharge power, open-circuit voltage and discharge instructions will be calculated. After that, influences of three factors mentioned above will be analyzed. On this basis, this thesis proposes an improved control strategy which indirectly adjusts output power ratio of rectifier to energy storage device by modifying changing the discharging voltage instructions. The effect of improved control strategy is verified through simulation compares. According to the results of influence of wide voltage operation range, an improved control method which is based on voltage differential and variable gain control is also givenFinally, using the supercapacitor energy storage experiment platform a series of experiments are taken for verifying new control method. By compassions between conventional control method and the improved control method, theoretical calculation results and experimental results, the accuracy of theoretical derivation and improve the effectiveness of the proposed control strategy is verified.