Study On Modeling And Dynamic Stability Of Synchronverter-Dominated Microgrid

Microgrid is an independent power distribution system composed of distributed power supply,energy storage device,power electronic conversion device,and various power load units.It is an important means to make full use of new energy.As the synchronous motors widely exist in the traditional power grid,the inverter interfaced distributed power supplies are used in a large number.And the expansion of the scale will lead to the reduction of the moment of inertia and rotating spare capacity.Synchronverter technology can compensate the loss to a certain content because of the introduction of inertia in the control link.With the promotion of the technology,modeling and dynamic stability analysis of the microgrid based on Synchronverter will become a problem to be solved urgently.In this paper,a quasi-steady-state state space model of the whole-order Synchronverter based microgrid is established.The singular perturbation method is then used to realize the order reduction.Bifurcation theory is adopted to analyze the dynamic stability of the reduced order model and find the stable operation boundary of the microgrid system.Furthermore,the dynamic phasor method is used to model a balanced and unbalanced microgrid system.Main contents of this paper include:(1)Model establishment and simplification of Synchronverter based microgrid.Firstly,the modeling method of Synchronverter,network line and load is studied.Secondly,in PSCAD,we build a microgrid system with three Synchronverters as the power supply.And the whole-order state space model of the system is established.(2)By using the idea of singular perturbation method,under the premise of guaranteeing the dominant characteristics of the system,we separate the fast and the slows variables and change the form of the equations into singular perturbation form,By controlling the perturbation parameters,we realize the order reduction of the whole-order model of the studied system.(3)Dynamic stability analysis of micro-grid based on bifurcation theory.First,analyze the participation factors and find the parameters which have great influence on the dynamic stability of the microgrid system.Select these parameters as the bifurcation parameters and use the continuation method to track and draw the equilibrium manifolds of the system.Use the detection function to locate bifurcation point on the manifolds,and construct the stable running boundary of the microgrid system.Finally,the results of the bifurcation analysis are compared with the simulation results of the time domain to verify the correctness of the bifurcation analysis.(4)Establishment of dynamic phasor model and stability analysis of asymmetry microgrid system.Based on the dynamic phasor method,the model of the balanced and the unbalanced microgrid system is established.Then we verify that using the dynamic phasor model can solve the problem of analyzing stability of unbalanced system.Meantime,it can achieve a faster calculation speed than electromagnetic simulation.