Research On Operation Control Of Energy Storage Converter For Multi Scenario Application

Energy storage system stores electric energy through certain media and ways,and releases it through energy conversion or power generation when needed.PCS is the interface between energy storage system and external system.Different application scenarios have different requirements for PCS.Among them,precise power control and grid connected unplanned islanding smooth switching are contradictory under the background of grid voltage fluctuation,which cannot be solved by traditional control strategy.Due to the lack of relevant standards in the field of energy storage,PCS is difficult to be compatible with a variety of application scenarios.In this paper,the operation control technology of two-stage energy storage converter is studied,and a PCS that can meet the requirements of multi scenario application is designed.The former 3L BDC(three-level Bidirectional DC-DC)module in the two-stage PCS is responsible for the establishment of the intermediate DC bus voltage,and the unified control strategy is adopted for charging and discharging.The small signal model of 3L BDC is established,the bus voltage control strategy,neutral point potential balance control strategy and modulation method are studied,and the parameters of DCDC module are designed.The mathematical model of DC-AC module in two-stage PCS is established in two-phase rotating coordinate system.The mathematical model of synchronous generator is established,and the equivalent implementation process brtween the VSG algorithm and traditional synchronous generator is given.The pre synchronization method is studied to ensure the smooth switching between off grid and grid connect when the traditional VSG control is applied to the DC-AC module of PCS.When PCS is used for peak and valley regulation,it needs to accurately respond to the superior power command.In grid connected mode,fluctuation are existed in grid voltage which leads to inaccurate power control and static error of reactive power control.In this paper,an improved VSG control method is studied.By feedforward grid frequency and voltage amplitude and adding capacitor voltage closed loop in reactive power control loop,the influence of grid fluctuation on power control and static error of reactive power control are effectively suppressed without affecting the effect of off grid switching.The small signal models of voltage fluctuation to power under the traditional VSG control and the improved VSG control are established respectively.The system performance under the two conditions is analyzed and compared in detail,and the simulation is completed to verify the correctness of the proposed method.Finally,the experimental platform is built and the experiments of two-stage PCS are completed.The effectiveness and feasibility of bus voltage control strategy,modulation method,neutral point potential balance control strategy,smooth switching method of DC-AC module and improved VSG control method are verified.