| The global energy interconnection has been widely recognized at home and abroad,it promotes to use more clean energy instead of fossil energy.However,the large-sale integration of clean energy such as wind power or solar power will cause great challenge to the frequency stability of the power grid.Especially in the Three-North region of China,most of the frequency modulation units are thermal power units,who’s frequency modulation capability and performance is low.At the same time,emerging energy storage technology,with the fast and accurate power adjustment characteristics,while assisting with the thermal power units,may be an effective supplementary means of frequency modulation.Firstly,the paper analyzes the working principle of primary and secondary frequency regulation of the thermal power units and analyzes structural composition as well as operation structure of large-scale energy storage system.Then dynamic models of DEH governor,steam turbine,CCS coordinated control system and boiler as well as circuit models of energy storage module,VSC and DC/DC converters are built based on PSCAD/EMTDC.Further more,a expansion model has been proposed based on Bergeron model,which can simplify the system consist of same or similar parallel subsystems.Secondly,proposes the whole control strategy for energy storage system assisting with thermal power units on frequency modulation based on hierarchical control by considering the pros and cons of energy storage system and thermal power units.Finally,based on the built simulation and theoretical model,analyzes the influence that the main unit speed control system parameters have on the dynamic frequency characteristics,and analyzes the thermal power units frequency modulation characteristics with the assist of energy storage system,and proved that the control strategy proposed by this paper can improve the frequency modulation capability and performance of thermal power units effectively. |
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