Inertia And Damping Combination Optimal Control Of Virtual Synchronous Generator

With the large-scale and centralized access of new energy sources such as wind power and photovoltaic,grid-connected inverters with power electronic devices are widely used.Because power electronic devices do not have the characteristics of rigid body rotation inertia,it will lead to the loss of inertia and damping of the system.By applying the virtual synchronous generator(VSG)technology,traditional control equations of synchronous generator are introduced into the control strategy of grid-connected new energy inverter,thus providing necessary inertia and damping for the system and strengthening frequency and voltage support ability of power grid.Considering that virtual synchronous generator simulates the operation characteristics of synchronous generator,it will cause similar stability problems.However,the flexibility of VSG control parameters can be used to offer innovative ideas for stability improvement.For this purpose,this paper starts from the control technology of virtual synchronous generator,and explores the control parameter optimization method and adaptive control strategy of virtual synchronous generator to improve the stability of power grid.Firstly,the development of virtual synchronous generator technology is summarized,and the summary of existing VSG projects is introduced.On the basis of analyzing VSG control technology,the current research work for stability problems caused by grid-connected VSG is summarized from two aspects:small signal stability and transient stability.Secondly,the traditional control strategy of the grid-connected new energy inverter is summarized.With the introduction of active and reactive power control equation of synchronous generator,the overall control strategy of VSG is established and analyzed based on VSG control principle from two aspects:active power-frequency and reactive power-voltage.According to the MATLAB/Simulink simulation results,the VSG model has the characteristics of inertia and damping,which shows the validity of virtual synchronous generator in frequency support capacity.Then,based on differential inclusion theory,a small signal stability analysis method with uncertain power system is proposed.By using the polytopic linear small signal model,the power system with uncertain stochastic excitation is characterized as a convex hull with finite element.The small signal stability criterion of polytopic system is derived based on the convex hull Lyapunov function.On this basis,the control parameters optimization method of multi-VSGs is proposed by using eigenvalue placement method to ensure the damping characteristics of system in steady-state operation.By establishing the simulation example of WSCC three-machine nine-bus system,the validity of proposed small signal stability analysis method and parameters optimization method are verified.Finally,in order to further reduce the dynamic response and oscillation time under transient disturbance,an adaptive control method of VSG inertia and damping is proposed based on the optimization model in oscillation process,which makes full use of flexible adjustable advantages of VSG control parameters.By applying the same inertia and damping control of each virtual synchronous generator on the same bus all the time,effective suppression of the oscillation with multi-VSGs in parallel is realized based on the operation state at the end of oscillation.The validity of proposed adaptive control method is verified by simulation example of a typical microgrid.