Study On Simulation Modeling And Protection Of Microgrid

Traditional grid has some problems,such as the problem of power supply,energy crisis problem,and electricity can not be used reasonably and efficiently.So micro-grid emerges as the times require.Although micro-grid has many advantages,however,it brings some problems to the grid due to the access of distributed generation to micro-grid will lead to some adverse effects.First of all,the access of distributed generation.First the topology structure of the network has been changed from the traditional electricity supply mode with a single supply voltage to multipl distributed generation supply electric power.So it caused some problems such as bi-directional current existed.Second a large number of power electronic devices are contained in the distributed generation,what made a large difference in the short circuit between the traditional grid and micro-grid.So we should consider both of the bi-directional current and the change of short circuit when we solve the relay protection problem of the micro-grid and the efficient protection scheme should be put forward.We modeled and analyzed different kinds of distributed generation and established micro-grid in this paper.After profoundly analysis for relay protection problem of micro-grid interconnection of grid and the influence of the containing micro-grid fault characteristic,a sequence component protection scheme to improve differential current method is proposed.The faults in the grid model are simulated and analyzed,the feasibility of the protection scheme is verified.Concrete study content as follows:Firstly,the characteristics and the control principle of the distributed generation with inverter-based interface are analyzed.According to the mathematical model in dq frame,PQ and V/f control structures are designed.Some frequently-used distributed generation are introduced and analyzed.According to different kinds of distributed generation supply for mathematical modeling based on PSCAD software,analyzes grid topology modeling.In order to guarantee the stability of the grid voltage and output,the control of inverter using different control methods.Secondly,micro-grid model was build based on the model of distributed generation.The difference between the grid contains micro-grid failure and traditional electrical protection are analyzed,it analyzed the fault occurred in the influence of different position of micro-grid relay protection from the distributed generation accessposition,micro power supply capacity of the two aspects;It analyzed the impact on the automatic reclosing because of micro-grid.Lastly,the main protection strategies of micro-grid are analyzed,and against the problem that upstream region of single-phase ground fault can't be detected by differential current method,this paper put forward a protection method based on sequence component,which can cover the shortage of differential current method.In consequence,this paper proposed improvement program the combining the two methods,which can reach a good protection effect.Using the model of micro-grid to make simulation make sure of the feasibility of the protection scheme that based on sequence components.