Research On Inverter Control Strategy For Virtual Synchronous Generator In Microgrid

The generation of electric energy has brought about a great change in the history of human civilization-the arrival of the electrical era,and now all aspects of our lives are inseparable from electric energy.With the increasing energy consumption,it is more and more important to use photovoltaic,wind and tidal energy for distributed generation.However,directly incorporating a large number of distributed generators into the grid will bring adverse effects to the grid,and the introduction of micro-grid successfully solves this problem.In micro-grid,due to the large use of power electronic devices,micro-grid lacks inertia and damping.Even small load changes will lead to sudden changes in the frequency of micro-grid,thus affecting the safety of electrical equipment.These problems can be solved by improving the control methods of micro-grid.This paper will improve the frequency quality of power grid by improving the control method of microgrid inverters.Firstly,on the basis of analyzing the advantages and disadvantages of traditional microgrid control methods,a microgrid control method based on virtual synchronous generator control theory is designed by referring to the good frequency quality caused by large inertia and strong damping of synchronous generators.Based on the second-order mathematical model of synchronous generator and the output characteristics of synchronous generator,the mathematical model of virtual synchronous generator is established by analogy to the microgrid inverters.Then the VSG ontology,virtual speed regulator and virtual excitation controller of virtual synchronous generator are designed respectively.After the establishment of the mathematical model,the control technology of virtual synchronous generator is improved.From two ideas,one is to improve the VSG model,the other is to improve the setting of its key parameters.Through the comparison and analysis of the two improved schemes,it is concluded that reasonable design of key parameters of virtual synchronous generator can easily and quickly adjust the frequency of microgrid and restrain frequency mutation.Then a virtual synchronous generator control scheme with adaptive control of moment of inertia and damping coefficient is designed,and the improved scheme is simulated and analyzed.The experiment is based on the MATLAB simulation platform.The design of the experiment includes two parts: simulation under no-load and simulation under load.It is concluded that the control method can maintain the fluctuation of power grid frequency in a small range and improve power quality in the case of large load fluctuation.The simulation results verify the effectiveness of the proposed method.