Research On The Voltage-type Control Strategy Of Microgrid In Grid-connected Mode

In the new century,with the rapid development of industry and economy,some non-renewable fossil energy is shortage.Then renewable energy has gradually become an important direction to develop and utilize.With the development of human research in the field of new energy,photovoltaic power generation technology has become a research hotspot.Photovoltaic inverter is an important part of the photovoltaic power generation system,thus the study of its control strategy is of great practical value.To further improve PV utilization,the PV microgrid has been put forward.It integrates photovoltaic inverter unit,energy storage unit and other distributed units.It has good autonomy and compatibility with traditional power grid.The specific research contents are as following:The technologies of grid-connected and parallel connection are compared and analyzed.The principle of droop control is analyzed and deduced in detail.Besides,the droop control technology applied to the grid is deeply studied.For the problem that,when droop control applied to the actual grid connection,vulnerable to the grid frequency and amplitude fluctuations,this paper proposes an improved grid connected control technology.The parallel inverter system is controlled by droop control to achieve parallel connection and upgrading capacity,and guarantee power supply quality to the greatest extent.In order to solve the problem of grid current harmonics incorporated into the actual power grid,this paper analyzes the causes and mechanisms of the harmonic generation of grid connected current,and proposes an improved grid connected control strategy based on harmonic compensation.The control strategy realizes the grid connected inverter with drooping control without obvious distortion and grid connection,and improves the power quality of the grid connected current.Based on the typical topology of the parallel system of two stage inverters and the proposed improved droop control strategy,a small signal mathematical model of the parallel system is established.The stability and rationality of the control algorithm are verified by using the Root locus method,and the stability interval of the control parameters is determined at the same time.The discrete simulation model of parallel inverter system is built by using MATLAB simulation.The simulation results demonstrate the effectiveness of the proposed strategy.