| With a wide range of applications of large-scale distributed power, the energy storage device is becoming more and more important for the power grid, which plays a role as load shifting, stabilizing fluctuations in output power of distributed power and the emergency power supply. The battery is an important classification of the storage device, and lead-acid batteries and lithium batteries are widely used. Power electronic converter is the interface connected to the grid or micro-energy storage for the battery, including bidirectional buck-boost chopper circuit, single-phase full-bridge inverter circuit and three-phase half-bridge inverter circuit. The converters used for the battery can not only operate in the grid-connected mode, but also in the off-grid mode, so called dual-mode inverter. This thesis studies the dual-mode inverter and the research works are as following.Firstly, establish a mathematical model for the storage battery dual-mode inverter (including off-grid and grid-run operation) in different coordinate systems, and analyze the principle and implementation methods of SVPWM.Then, design varies operating modes and implementation process of the dual-mode inverter according to the demand of the actual project. The state of charge of battery, the state of the power grid and the output of distributed generators are the continuity constrains for operating modes.Thesis focuses on the operation modes, the related control strategies and smooth handoff control methods of battery storage inverter:(1) on-grid mode, uses double closed-loops control strategy. When the inverter is used to stabilize the fluctuations of DG, the reference of the out-loop is given by the dispatching center and the feedback value is the real active power; the inner-loop is for the current of the filter;(2)when used to charge the battery, select corresponding of charging way as constant pressure charging, and constant stream charging;(3) select outside ring limited site value for rated power, to avoid incorporation actual run mode switch led to storage can inverse changed players appeared had stream situation;(4) when away from network run, take single ring control, control target for local load end voltage;(5) made take grid voltage plus or minus sequence component as standard judgment grid state of method, for in grid fault or from fault in the recovery occurred of incorporation/away from network switch, compared to active type island detection, can cover cannot judgment grid fault recovery of defects;(6) made from incorporation switch to away from network run of method is, Incorporation run records grid voltage site value phase, judgment out grid occurred fault, to normal Shi of site value phase according to50Hz of frequency constructed reference voltage, guarantee load end voltage not occurred mutations;(7) made from away from network switch to incorporation run of method is, grid from fault in the recovery, to grid phase on load end voltage phase for coordinates transform, begged out phase difference and site value poor, adjustment inverse changed players output voltage until phase difference and site value poor for zero, then closed incorporation switch.Systematic theory in the analysis of papers based on PSCAD/EMTDC simulation platform to build a complete energy storage system (dual-mode inverter) model was validated on these various control strategies.Actual projects, developed a30kVA energy inverter prototyping and testing of control strategies, and achieved good results. |
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