Research On Multi-functional DG Module Unit And Control Of Microgrid

With the rapid development of national economy,such excessive reliance on coal,oil,natural gas and other fossil fuels in industrial and daily life led to a serious deterioration of the environment nowadays,which makes an growing depletion of resources.In order to explore and develop clean energy,China has begun to support new energy research and development,wind energy and solar energy are included as the main form of clean energy.Distributed power generation can convert renewable energy into power.In the recent years micro-grid has been widely study since it solved the uncontrollable unit distributed power on the impact of large power grids to a certain extent.In the mean while,it has independent capacity as a special structure of the power generation system,which can incorporate renewable micro-source,power storage,local load,quality control and control unit of the local power supply system in one of the micro-grid module unit.Micro power grid is integrated with many kinds of micro-source and local load to connected grid,store energy,restrain the harmonic and other functions,but have not yet formed a unified on structural topology structure or any standard.Thus this paper proposes a new basic network layer standard unit-micro-grid DG module unit,the structure are constituted by voltage inverter,current inverter,local load,the public bus composition.The structure can meet the micro-grid in the multi-standard unit convergence and expansion of the demand;also can be achieved when the island bus voltage unbalance,current THD,and inhibit the bus voltage imbalance,and the network can control the entire unit operating mode to achieve hierarchical control.This paper presents a direct sequence space vector voltage direct compensation method to suppress the influence of the negative sequence component of the bus voltage on the bus voltage in order to ensure the balance of the bus voltage.And as a result of the existence of non ideal grid conditions,this paper proposes a general-purpose plural controller,according to the different types of non ideal grid situation to deduce a series of quasi PCI control cluster,which can effectively inhibit the impact on the grid current non-ideal grid.A general type complex controller is proposed in this paper to derive aseries of quasi-PCI control clusters according to different types of non-ideal power grid,which can effectively suppress the impact on non-ideal grid-to-grid current.Finally,according to the negative sequence vector voltage direct compensation method proposed in this paper,the general type complex controller is simulated and verified by building an experimental platform of DG module unit system with two diode-clamped three-level inverters using DSP and FPGA to realize the proposed digital control.The experimental results show that the proposed two control strategies can effectively suppress the influence of the unbalanced load on the bus voltage and the influence of the non-ideal voltage on the grid-connected current.Thus effectiveness and feasibility of the proposed control strategies are verified experimentally.