Improved Power Decoupling Strategy For Virtual Synchronous Generator

With the gradual globalization of fossil energy depletion,distributed generation technology based on photovoltaic,wind energy and other renewable energy has emerged as the times require.Although it has the advantages of fast response and high signal transmission efficiency,power electronic devices do not have the ability to suppress disturbances,and a large number of access will reduce the total inertia coefficient and total moment of inertia of the microgrid system.Virtual Synchronous Generator(VSG)uses the mechanical equations of the traditional synchronous generator(SG)frequency and voltage regulation mechanisms as a reference,and incorporates inertia and damping algorithms in the control loop,giving VSG external characteristics similar to SG.However,when VSG is connected to a weak current network,the impedance of the power grid often presents resistance inductance,and the impedance ratio is often large,leading to serious power oscillation problems and further exacerbating power coupling.This article mainly studies the coupling problem between active and reactive power after VSG grid connection,as well as control improvement.The specific content is as follows:Firstly,a grid-connected model considering line impedance,power angle and other factors is established,and the harmonic linearization analysis is carried out,the reasons of output power coupling caused by impedance ratio,power angle and interaction between active and reactive power loop are described.Secondly,a virtual negative impedance method is proposed for high impedance circuits.The virtual resistance in the virtual negative impedance link is used to offset the resistive component in the circuit,and the virtual inductor is added to make the equivalent output impedance of VSG more sensitive.The closed-loop control model of voltage and current with virtual impedance is established,and the parameters of virtual negative impedance are controlled by interval method to ensure the stability of the system.A control method based on current dynamic compensation is proposed for power angle.In order to verify the effect of power angle change on decoupling performance,the Control Link of active power input to VSG output frequency instruction is introduced,the output characteristics of VSG are not changed while the system stability is guaranteed.In order to ensure the effectiveness of decoupling,current imbalance and power oscillation caused by voltage fluctuation are suppressed by controlling different negative sequence current instructions.The simulation results show that the proposed strategy is effective in suppressing oscillations.Finally,this paper uses the hardware equipment with YXSPACE SP2000 as the core and the supporting software library to build a VSG experimental platform.The results also preliminarily verify the feasibility of the strategies proposed in this paper.