Study On Oscillation Characteristics And Active Suppression Measures Of PMSG At Sub/Super Synchronous Frequency

PMSGs which are connected to the grid through full-power inverters have obvious advantages in low voltage ride through and unit maintenance costs,and have gradually become the mainstream of development.However,the fast response characteristics of power electronic converters make PMSG and the grid be coupled to each other,inducing a new sub/super synchronous oscillation problem,which greatly threatens the safe and stable operation of the power system.In view of the study of oscillation characteristics and active suppression measures of PMSG under sub/super-synchronous frequencie,the main contents and results of this paper are as follows:Aiming at the sub/supersynchronous oscillation of PMSG connected to the grid,this paper constructs a transient energy function model based on the structure of PMSG in electromagnetic transient time scale,and analyses the transient energy composition of PMSG.Then,based on the superposition of sub/supersynchronous frequency component and fundamental frequency component,the expression of oscillatory energy which can directly reflect the development trend of sub/supersynchronous oscillation is derived.The damp characteristic of PMSG to sub/supersynchronous oscillation is judged by the positive or negative oscillatory energy.The simulation of grid-connected PMSG system verifies the correctness of the transient energy model.In order to solve the problem that the control links of PMSG and SVG are mutually coupled in the process of sub/supersynchronous oscillation,which is not conducive to the analysis of oscillation characteristics,an analysis method of oscillation characteristics based on the oscillatory energy of control links is proposed in this paper.Firstly,considering the dynamic change of the output of PLL in the process of sub/supersynchronous oscillation,the output instruction value of the closed-loop control system in converter is derived and substituted into the transient energy function.Then approximate decoupling is obtained from the control time scale,and the transient energy part dominated by each control link is defined as the oscillatory energy provided by the control link.Finally,the positive or negative oscillatory energy is used to judge its role in the sub/supersynchronous oscillation process.The simulation results of grid-connected PMSG and parallel SVG system show that the PLL loop provides positive oscillatory energy during the sub/supersynchronous oscillation,which easily leads to oscillation divergence,while the current loop is opposite;the oscillatory energy of SVG under constant reactive power control mode is less,and it is relatively stable in the sub/supersynchronous oscillation.Aiming at the problem that the existing subsynchronous/supersynchronous oscillation suppression measures are not suitable for multi-frequency oscillation scenarios,and the SVG control strategy is not taken into account,an active subsynchronous/supersynchronous oscillation suppression method based on parameter adjustment is proposed in this paper.Firstly,according to the expression of oscillatory energy and the positive or negative situation of each control link,the influence of changing the parameters of single control link on the overall oscillatory energy is analyzed,and the boundary conditions for reducing the oscillatory energy of corresponding control link are obtained.Then,considering the limitation of basic voltage,frequency and other indicators on the adjustable range of parameters,a unified multi-constrained parameter optimization adjustment model is established.Finally,the Particle swarm optimization(PSO)algorithm is used to find a reasonable combination of parameters to achieve active oscillation suppression.The simulation results show that the proposed parameter adjustment strategy can effectively reduce the oscillation amplitude and realize the active suppression of the sub/supersynchronous oscillation...