Research On Distribution. Electronic Power Transformer Based On Hybrid Energy Storage System

In modern electric power system, the type of load and power form have changed profoundly, consumers" demand for power quality and power supply reliability are getting higher and higher. As a new type of electric energy conversion equipment, electronic power transformer has reformed the functions of traditional power transformer in improving the power quality of distribution system. However, there is no specialized energy storage unit in electronic power transformer, which can not compensate power interruption and voltage sag during power supply. Yet, power interruption and voltage sag have been considered as the most serious dynamic power quality problems that affect the safe and stable operation of many power equipments. Therefore, the research on electronic power transformer applied with energy storage technology is of great significance in improving the reliability of power supply and ensuring the safe and stable operation of power equipments.Firstly, the topological structure and working principle of distribution electronic power transformer are discussed, under the background of power quality problems in modern power system, the application characteristics in distribution system and the power quality regulation and control capability are analyzed, analysis result shows that electronic power transformer can not deal with the power interruption and voltage sag properly. Based on the analysis of the mathematical model of three-phase VSC(Voltage Source Converter), the mathematical model of AC/DC/AC three stage electronic power transformer is established and the control strategy of each stage is designed, the performance of each stage is verified by simulation.Subsequently, according to characteristics of battery and super capacitor, the hybrid energy storage system is composed by taking advantages of both components and applied to electronic power transformer to study its compensation effect on voltage interruption and voltage sag. In view of the specific application in electronic power transformer, the operating modes of hybrid energy storage system are analyzed in detail, and the energy management strategy of the hybrid energy storage system is designed. Bidirectional DC/DC converter, as the key of energy management, its mathematical model of Buck and Boost state is deduced in detail, combined with the different working modes of hybrid energy storage system, the bidirectional DC/DC converter's controller of battery and super capacitor are designed.Finally, under the condition of power interruption and voltage sag, considering the load demand for energy, the energy storage capacity is designed. A simulation model of electronic power transformer based on battery super capacitor hybrid energy storage system is established by using Simulink, three conditions respectively for stable operation of power grid,voltage interruption and voltage sag are simulated and analyzed. The results show that the electronic power transformer has good performance, which can meet the demand of sensitive load for high power quality. Through the flexible control of battery and super capacitor, the charging and discharging process of the battery is optimized. Compared with the electronic power transformer that without energy storage unit, electronic power transformer based on battery super capacitor hybrid energy storage system can compensate the power and energy of the load, improve the reliability of power supply to ensure the safe and stable operation of power equipment.