| At present,China has vigorously promoted the research and application of renewable energy to develop a green and low-carbon microgrid system.However,renewable energy has problems such as uncertainty,volatility and intermittency,so energy storage systems are used to provide functional support for microgrids to achieve stable and efficient operation of the power grid.This paper studies the control strategy of hybrid energy storage array system(HESAS)in DC microgrid,and the main research content is as follows:(1)The HESAS model was established,and the hierarchical control strategy architecture of HESAS was studied.The HESAS model mainly includes three parts: battery model,supercapacitor model and bidirectional DC/DC converter model.The control architecture of HESAS commonly uses hierarchical control: the upper layer mainly adopts the frequency division method to achieve power distribution;The lower layer generally adopts distributed hierarchical control to realize the control of voltage and current.The control architecture provides an idea for the HESAS hierarchical coordinated control strategy based on model predictive control(MPC)proposed later in this paper.(2)Aiming at the problem of HESAS coordinated operation in DC microgrid,this paper proposes a hierarchical control strategy based on MPC.The upper control adopts centralized control,first using wavelet packet conversion to obtain the power of each supercapacitor and battery pack,and then considering the different capacity and initial SOC in the battery pack,an adaptive factor consistency strategy based on battery SOC is proposed to redistribute the power of the battery pack to achieve battery SOC consistency.The lower control adopts distributed control,based on the bidirectional DC/DC converter model,and proposes a finite control set model predictive control(FCS-MPC)strategy,which assigns the given value of bus voltage and the upper power to a fixed value as a reference value,predicts the current and voltage,and designs the objective function with the sum of the squared deviations of voltage and current,obtains the optimal control signal through the finite state comparison,and finally realizes the optimal control of voltage and current.(3)Aiming at the problem that the above hierarchical control strategy occupies a lot of communication resources,an event-triggered communication method is proposed to alleviate the communication pressure of coordinated control of multiple energy storage units.Firstly,the core event trigger function is designed based on the bus voltage deviation and the output power deviation of each energy storage unit.Then,the auxiliary event trigger function is designed to improve the core event according to the deviation between the received SOC value and the actual SOC value of the upper control.Finally,the SOC difference between batteries is designed to determine whether the core event and the auxiliary event are effective.In this paper,a DC microgrid model containing HESAS is built on Matlab/Simulink,and the simulation results show that the layered control strategy based on MPC can effectively realize the power coordination control of HESAS.Event trigger control effectively reduces communication time and saves communication resources. |
