Research On Power Sharing And Smooth Switching Control Technology In Microgrid

Microgrid is a small regional power grid composed of distributed generation unit,energy storage unit,load unit and control unit.The distributed units within the microgrid need to share load power proportionally in order to improve energy efficiency.At the same time,they should have combined and offline functions to improve the flexibility and security of the system.However,under actual operating conditions,the influence of line impedance will lead to the reduction of the accuracy of traditional power sharing control method,and the impact of On-grid/off-grid switching control process seriously threatens the stable operation of microgrid.In view of this,this paper focuses on power sharing technology and smooth switching technology to improve the energy efficiency and security and reliability of the microgrid.The specific work is as follows:Firstly,this paper introduces the background of the subject and the structure of the microgrid,establishes the mathematical model of the inverter,analyzes the control technology of distributed generation,summarizes the characteristics of the overall control technology of the microgrid.And research on phase-locked loops,voltage and current control,and pre-synchronization control techniques.Secondly,the microgrid is affected by the line impedance under the operation of the island mode.The traditional control technology is difficult to distribute the power reasonably,resulting in reactive circulating current between the distributed power sources,which affects the stability of the system.In order to solve the above problems,this paper proposes an adaptive droop controller.In this technique,the no-load voltage is automatically adjusted to eliminate the voltage drop due to the variation of the droop gain,so that the reactive power of the two micro-sources is evenly distributed to maintain the system voltage stability.Through the analysis of control mechanism,under the condition of power load disturbance,the traditional and improved droop control algorithms are simulated and analyzed by using MATLAB/Simulink,which verifies that the improved droop control technology improves the reactive power sharing accuracy of microgrid.Thirdly,in the low-voltage microgrid,due to the impact of the voltage and current running off-grid,this paper further proposes a smooth switching control technology based on the control state follower.In this technique,the PQ control mode is used for grid connection and the droop control mode is used for islands.At the same time,the pre-synchronization control is improved,and the output of the PQ controller or the droop controller is used as the input of the other controller to form a smooth switching control method in which two different controllers follow the synchronization.Then the simulation technology is simulatedand verified to verify the effectiveness of the proposed strategy.Finally,based on the experimental platform of new energy and microgrid,the connection between two photovoltaic,energy storage and grid is realized,and the smooth switching control technology test is completed.Experiments show that the technology can reduce the voltage and current impact and achieve smooth switching when parallel switching off the grid.