Research On Stability Mechanism And Parameter Tuning Of Virtual Synchronizer Based On Small Signal Model

With the global energy and environment issues worsening,renewable energy has developed rapidly due to its huge potential for development and environmentally friendly characteristic.This makes the penetration rate of renewable energy power generation equipment in the grid increase and the inertia of the grid reduce.The too lower inertia leads to rapid fluctuations in system frequency,which worsens the system's ability.To solve this problem,some researchers proposed an algorithm called Virtual Synchronous Generator(VSG).In order to supply the voltage and frequency regulation service for the system secure operation,this algorithm simulates the inertia,the frequency modulation and voltage regulation characteristics of the synchronous generator running in the gridconnected inverter controller.Although the algorithm improves the frequency stability of the system by introducing inertia loop,it deteriorates the power angle stability of the system.In this paper,the small signal stability of virtual synchronous generator is studied.The major contributions of this paper are as follows:(1)Based on the mathematical model of synchronous generator,this paper introduces the VSG control algorithms in detail which are commonly used,and elaborates the similarities and differences between these control strategies.(2)This paper establishes a small signal model for VSG with robust control.Then,by analyzing the participation factors of this model,it is found that the higher order model provides a higher oscillation mode that is a weakly correlated with power oscillations.Thus,this paper proposes to describe the dynamic characteristics of the filter and the line by using the steady-state equation,and obtains the reduced-order model and error expressions of the system.Subsequently,the analysis of the eigenvalues,the main correlation state variables and the error expressions show that the reduced-order model can acquire the low-frequency eigenvalues with high precision.In addition,the paper also analyzes the application of two small-signal models using parameter sensitivity and root locus.(3)This paper compares the small signal block diagrams of synchronous generator and virtual synchronous generator.It is found that the two small-signal models can be equivalent under some conditions.Based on the analysis method in the traditional power system,this paper defines the virtual torque coefficient of the VSG with reactive power and voltage loop,and discusses the relationship between the coefficient and the stability of the system from the perspective of mathematical model.Then,the conclusion is verified by the simulation and experiments,and the use of the virtual torque coefficient to analyze the mechanism of system parameters and controller parameters on system stability is introduced.