Control Strategy Of Micro-Grid LVRT Based On Stability Controller

The dual pressures from resources and environment make energy development strategy must be transformed.Wind power and photovoltaic power has been the strong support of national policy as the representative of renewable energy.As an important form of renewable energy utilization,micro-grid doesn’t have so much influence on main grid,and it can also improve the reliability of regional power supply and the power quality of distribution network.The operation mode of micro-grid is more flexible,and the external characteristics is controllable which can realize the efficient utilization of renewable energy.As a key technology of distributed generation,micro-grid technology has attracted wide attention.Large scale renewable energy generation(wind farms,photovoltaic plants,etc.)only need to ensure itself not be off the grid for the specified time when grid voltage sag occurs,and there is no hard requirement for the power quality of PCC(Point of common coupling).Different with large scale renewable energy generation,micro-grid need to ensure the reliability and power quality of PCC.Because it directly connects to the distributed network.When the grid voltage sag occurs,the micro-grid should be as much as possible to ensure that the consecutive power supply and normal operation of the load.Based on the existing conditions,energy storage devices configuration in the system can be an effective solution.Firstly,the main circuit parameters of micro-grid stability controller(MSC)are designed in this paper,and the mathematic model of micro-grid stability controller is deduced based on the relevant parameters.The stable operation of isolated mode and grid-connected mode is also realized.Furthermore,a two-mode stability controller based LVRT(Low voltage ride through)strategy was implemented by incorporating low voltage distribution network parameters and voltage characteristics.By monitoring the main grid voltage,the optimal operating adjustment strategy was selected automatically for the controller including active power injection adjustment and microgrid operating mode switching,in order to maintain the voltage stability of the point of common coupling(PCC).The simulation and experimental results demonstrate that the proposed strategy could support the voltage of the PCC effectively,and implement microgrid LVRT considering actual system requirements.Finally,the low voltage ride through control strategy of asymmetrical voltage sag is analyzed,and a low voltage ride through scheme based on improved PR control is proposed.The simulation results show that the proposed control strategy can effectively limit the grid fault current and achieve low voltage ride through.