| Under the background of worldwide energy and environmental crisis,microgrid has become a development trend of saving energy consumption and improving the stability and reliability of power system.As a basic component of microgrid,distributed generator is clean and environmental.As the carrier of distributed generation,microgrid can fully to manifest the advantages of distributed generation technology.The microgrid can realize to work both grid-connected and off-grid operation mode,so it has the advantages of flexibility and economy.Firstly,this paper selected the most typical photovoltaic system and Direct-driven permanent magnet synchronous generator wind power system as the new energy generation forms in the microgrid,and deeply studied the mathematical model and grid-connected control method of the two generation systems.The completed grid-connected generation model is established,and then the grid-connected photovoltaic model and the grid-connected model of permanent magnet direct-drive fan are simulated and analyzed.Secondly,the paper related and analyzed the control mode of distributed generator based on inverter controlling method,the structure of microgrid and the control mode of the whole system are discussed.The typical master-slave control mode microgrid is in grid-connected operation,the external grid provided frequency and voltage reference for all distributed generators in the system.All grid-connected inverters were in constant power control mode.When the microgrid was in the islanding mode,it is necessary to switch the main control generator in the system to the constant voltage/constant frequency control mode.In this paper,the mathematical models of the battery and its converter were established by taking the battery as the main control unit of the system.Based on the battery converter,the control strategy of islanding mode and network mode were designed to realize the stable operation of microgrid in islanding mode and network mode.Based on each distributed unit,a master-slave control mode of wind-solar-storage microgrid was established.The simulation results showed that the model can run stably in network mode and islanding mode.Finally,the problem of voltage mutation and current shock in mode switching process of microgrid was studied.The switching control problem between network mode and islanding mode was always the key technology point in engineering research field.In this paper,the dual mode controller was studied and modelled,the compensation algorithm of reference current was designed to solve the transient current or voltage impulse caused by the problem of controller in typical master-slave microgrid switching mode.The simulation results showed that the proposed seamless switching algorithm can effectively improve the transient response of the microgrid in mode switching and realize seamless switching between two operation modes. |
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