A strategy of battery energy storage system coordinated with converter stations for smoothing power fluctuations of flexible DC distribution system

With its significant advantages, flexible DC power distribution system has been widely recognized. Flexible DC distribution network has complex components such as distributed power generation, BESS and power load, so the active power exchanged between DC distribution network and AC grid may have large random fluctuations, which affects the stable operation of AC grid. At present, there are no standard about the rate of power fluctuations when flexible DC distribution network is connected to AC grid. A standard was made that the maximum power change within 10-min should be less than 1/3 of the capacity of converter station. Based on a two-terminal structure, this paper presented a control strategy of BESS coordinated with converter stations to smooth power fluctuations. Firstly, the power of DC distribution network is distributed between two converters according to their capacity proportion, power fluctuations get suppressed preliminarily, through charging and discharging operation of BESS, power fluctuations can be smoothed further. To ensure the charging and discharging capacity of BESS, its SOC was controlled at about 50%. Finally, simulation was carried out in EMTDC/PSCAD, and the results showed the efficiency of the proposed strategy.