Research On Predictive Current Control Strategy Of Power Conversation System

With the continuous development of society and the improvement of people’s material living standards,the valley peak difference of power system load characteristic curve is increasing.The application of energy storage power station in power generation side,power transmission and distribution side and user side can effectively solve the problem of large valley peak difference and realize peak shaving and valley filling.In this paper,based on the background of low-voltage system user side electrochemical energy storage power station,PCS(power conversion system)as the research object,according to the technical index requirements of GB/T34120-2017,The control strategy of grid mode charging and discharging and the control strategy of islanded mode discharging,anti islanding protection scheme and grid and islanded mode switching function of PCS are studied.Firstly,this paper compares different topology types and selects NPC(Neutral point clamped)three-level structure as PCS topology.The operation principle of NPC three-level power converter and the mathematical model of PCS in grid and islanded mode are analyzed.The charging and discharging control strategy of PCS in grid mode is studied.Under the charging control strategy,two different current inner loops are used for comparative analysis: PI voltage feedforward decoupling current inner loop control and DBPCC(deadbeat current predictive control).It is found that DBPCC has faster dynamic current response and simpler control model than PI voltage feedforward decoupling control.This paper analyzes the control strategy of PCS based on the inner control loop of DBPCC.In the study of PCS grid mode discharge control strategy,aiming at the problem that users’ energy storage is forbidden to transmit power to the grid in Jiangsu Province,a P/Q discharge control strategy based on load real-time power is proposed,which can effectively solve the problem of power backflow during PCS grid mode discharge.The PCS islanded mode discharge control strategy,anti islanding protection scheme and switching between grid mode and islanded mode are studied.In the study of PCS islanded mode control strategy,aiming at the problem that the traditional V/F control can not effectively improve the three-phase voltage balance caused by load disturbance,this paper proposes a positive and negative sequence separation V/F control strategy based on DSOGI-PLL(dual second-order generalized integrator-phase lock loop),which solves the three-phase voltage imbalance caused by negative sequence component.Islanding detection uses active disturbance detection method.Aiming at the problem that the active disturbance component of traditional active disturbance detection method is too large,this paper proposes an active disturbance detection method based on periodic positive feedback,which effectively reduces the impact of active disturbance component on the system.The research of islanded and grid switching function is divided into two aspects: grid mode/islanded mode switching and islanded mode/grid mode switching.The control of grid mode/islanded mode switching is designed on the basis of PCS short power outage when the grid mode is switched to islanded mode.The islanded mode/grid mode switching control is designed based on PCS to ensure the continuous power supply of the load.The phase pre synchronization control method is adopted to realize the islanded mode/grid mode smooth switching.Finally,based on the PCS national standard test specification,the test platform is built to verify the charging and discharging control strategy.