Research And Optimization On Transient And Steady State Characteristics Of Virtual Synchronous Generator

In the face of the dual pressure of energy and environment,the development of renewable energy alleviates the traditional energy crisis to some extent,with the increasing penetration rate of renewable energy,the wide application of power electronic equipment changes the dynamic behavior of power system.Compared with traditional synchronous generators,power electronic equipment lacks inertia and damping,which is not conducive to maintaining system stability in case of power shock and failure outside the power system.The Virtual Synchronous Generator(VSG)control learns from the rotor swing equation of the synchronous generator,so that it has the inertia and damping characteristics of a rotating part.In this thesis,transient and steady state characteristics and optimal control of VSG during grid-connected operation are studied.The main research contents are as follows:First of all,this thesis analyzes the working principle of synchronous generator,deduces the stator voltage and rotor mechanical equation according to its mathematical model,deduces by analogy VSG reactive voltage loop control and active power frequency control by studying synchronous generator governor and excitation regulator,and combines voltage and current double closed-loop control to improve the dynamic response speed.Finally,the VSG overall control strategy is obtained.The equivalent relationship between VSG and synchronous generator is revealed,which provides theoretical basis for further study of VSG.Secondly,by analyzing VSG equivalent circuit,a power loop small signal model is established,and the small signal closed-loop transfer function of active power response under disturbance is obtained.The influence of virtual inertia J and virtual damping coefficient D on the system is analyzed,and the design method of main parameters is studied from the aspects of dynamic characteristics and stability margin.According to VSG power Angle characteristic curve,the angular frequency and frequency change rate of the system are analyzed,and the value principle in the interval J and D is determined.A kind of inertia damping adaptive control strategy is studied.Simulink was used to build a simulation model,compare and analyze the effect of traditional VSG and the adaptive control studied in this thesis,and the existing problems.Then,in order to solve the problems of parameter jitter in the adaptive control and the failure to take into account the transient characteristics and the steady state control accuracy,a VSG control strategy based on improved transient and steady state characteristics is proposed in this thesis.The improved transient power compensation can improve the transient gain of the system,and the transient damping can eliminate the influence of damping coefficient D on the steady-state error.By analyzing the influence of main parameters on the system stability in VSG control with improved transient and steady state characteristics,parameters design criteria are determined.Finally,simulation results show that the proposed control has good transient and steady state characteristics.Finally,the real-time simulation system is used to build semi-physical experiment platform,VSG control with inertia damping adaptive control and improved transient and steady state characteristics are experimentally verified,to verify the correctness and effectiveness of VSG control with improved transient and steady state characteristics proposed in this thesis.