Research On Adaptive Control Of Virtual Synchronous Generator For Weak Grid

In recent years,due to the rapid development of distributed power generation technology,a large number of power electronic devices,mainly inverters,have been connected to the grid.Due to the lack of inertia and damping of the synchronous generator rotor,distributed power generation poses challenges to the stability of microgrid operation.Virtual Synchronous Generator(VSG)technology can combine the control flexibility of electronic devices with the grid-connection friendliness of synchronous generators,enabling the inverter to actively adjust the grid voltage and frequency,significantly improving the micro The stability of the power grid.However,most of the new energy power generation is located in remote areas,and the distributed power sources are widely distributed.The power grid gradually shows the characteristics of a weak grid.The grid impedance is large and cannot be ignored,and there are nonlinear loads and harmonic voltages generated by the grid.Harmonic current.As a result,the stability of the system is reduced,and the VSG grid-connected current is distorted.To this end,this article conducts related research on how to improve the adaptability of VSG under weak grids.The main content of the paper is as follows:First of all,the mathematical model of VSG is established,the power frequency controller and excitation controller of VSG are designed,and the influence of different control parameters on power frequency characteristics is analyzed.The VSG power frequency small signal model is established and the simulation verifies the VSG Work characteristics.Secondly,the output impedance model of the VSG is established in the dq coordinate system and its frequency characteristics are analyzed.Based on the stability analysis method of impedance,the influence of different grid strengths on VSG operation is discussed,and the mechanism of VSG operation instability under weak grids is revealed.The influence of different power loop parameters on the stability of VSG under weak grid is analyzed.Thirdly,in view of the instability of VSG operation in weak grid,a series-parallel virtual impedance method is proposed to modify the VSG output impedance.This method does not affect the dynamic performance of the VSG itself,and greatly improves the stability of the VSG in the weak grid.Sex.Aiming at the problem of grid-connected current distortion caused by grid harmonics and nonlinear loads in weak grids,according to the equivalent harmonic domain model of VSG,a harmonic suppression method based on output impedance is proposed.This method makes the large nonlinear load Part of the harmonic current flows into the VSG side,and the harmonic impedance from the grid side to the VSG is increased to reduce the influence of the grid background harmonics,thereby improving the quality of the grid-connected current of the system.Finally,the proposed method was verified in MATLAB/Simulink,and at the same time,an experimental platform of VSG was built to preliminarily verify the feasibility and practicability of the VSG control strategy.