Coordinated Control And Aggregated Characterization For Distributed Energy Storage Systems In Isolated Power Systems

Energy storage can absorb and release energy and maintain the system power balance,which is an important means to promote the efficient use of energy and ensure the safe and stable operation of the system.Benifited from the flexible location and the rising installed capacity,distributed energy storage systems exhibt huge regulation potential.On the other hand,the isolated power system is a complement to the traditional interconnected grid.,which is helpful to reduce the cost of power supply,improve system performance and utilize new energy.It is regarded as one of the effective ways to achieve clean low-carbon and electrification.Affected by the random fluctuation of sources and loads,the isolated power system suffers from the unbalance power.Therefore,energy storage systems are required to compensate the unbalanced power.Based on the important role of energy storage systems in the isolated power system,it is necessary to study the coordinated control and aggregated characterization methods of distributed energy storage systems in the isolated power system.Therefore,the flexible control potential of distributed energy storage systems can be fully exploited to realize the stable operation of the isolated power system and thus help China’s energy transformation.In this paper,the reliable,accurate and economic operation of isolated power system is adopted as the typical scenario.And the study is carried out from perspectives of internal coordinated control and external aggregated characterization of distributed energy storage system.The specific contents and results of the study are as follows:(1)In the primary control layer of the ship isolated power system,the decentralized control applicable to multiple types of distributed energy storage systems is proposed to achive the system power balance under load fluctuations.By introducing the concept of virtual resistive branch circuit,the regulatory freedom of the method is extended without losing the actual physical meaning.Thus,the dynamic current-sharing among distributed energy storage is realized while quickly compensating the unbalanced power of the system.Simulation and experimention results show that the proposed decentralized control strategy based on virtual capacitance-resistance droop controller can effectively maintain system voltage stability and utilize multiple types of distributed energy storage.(2)In the secondary control layer of the isolated DC microgrid,the modified distributed voltage controller based on the proportional-integral consensus algorithm is proposed,to eliminate the steady-state error of the existing distributed distributed control.By designing the constraints,the proposed voltage controller is compatible with the existing distributed current controller.The modified distributed control can be constructed by the two kinks of distributed controllers.Simulation results show that the proposed modified distributed control can accurately achieve global voltage regulation and current-sharing among distributed energy storage systems under communication time delays.(3)In the secondary control layer of the isolated DC microgrid,the resilient distributed control with cascade structure is proposed,to address the steady-state operation point deviation of the system with the existing distributed distributed control under cyber attacks.The steady-state influence of the attack vector is eased by changing the control structure and communication variables of the distributed control.To further limit the voltage and current operating ranges,a state-active limiting strategy is designed by constructing virtual attack vectors.Simulation and experimention results show that the proposed resilient distributed control and state limiting strategy can effectively mitigate the steady-state deviations introduced by information attacks.(4)In the tertiary control layer of the isolated AC microgrid,the distributed state observer is proposed to estimate the aggregated parameters for the real-time characterization of the aggregation model of distributed energy storage systems.As a result,the issue of the dimension expansion by the large number of the distributed energy storage systems can be mitigated.Additionally,the distributed optimization algorithm is used to solve the optimization problem with the aggregation model to realize the optimizational operation berween distributed energy storage systems and other sources.The simulation results show that the proposed strategy can achieve dynamic estimation of distributed energy storage aggregation parameters and economic operation of the system.