Research On Virtual Synchronous Generator With Adoptive Virtual Inertia

In recent years,distributed generation based on renewable energy,with its advantages of clean and efficient,has received great attention in social development,and gradually become an important part of the power supply system.Most of the distributed energy such as solar energy and wind energy need to transmit power to micro grid or grid through the AC-DC-AC or DC-AC power electronic converter interface,i.e.grid connected inverter.However,distributed generation has the characteristics of dispersion,intermittence and real-time fluctuation.At the same time,the grid connected inverter itself cannot provide the rotary inertia with stable frequency for power system.The increasing penetration of distributed generation in power system will threaten the stability of grid operation.As a new strategy of grid connected inverter,virtual synchronous machine(VSM)control comes into being under this background.Through this control,distributed generation system can participate in grid regulation independently,and can effectively solve the problems of low inertia and under damping of distributed generation.Considering the slow dynamic characteristics,flexible parameter selection and restriction by the performance of the energy storage system of the virtual synchronous machine,this paper studies an improved adaptive control of the virtual synchronous machine based on the synchronverter virtual synchronous machine,which can optimize the frequency response curve.Firstly,according to the mechanical equation,the electromagnetic transient equation and the flux equation of the synchronous generator,the mathematical model of the synchronous generator is established;This paper introduces the topology of grid connected inverter used in virtual synchronous machine,and introduces the frequency and voltage regulation mechanism of active frequency loop and reactive voltage loop,self synchronization control strategy and switching between operation modes in detail.Secondly,the control parameters of the synchronverter virtual synchronous machine are analyzed in detail:J and D_p of the active frequency loop,K and D_q of the reactive voltage loop,which affect the response speed and stability of the power,frequency and voltage of the system;It is pointed out that there is a contradiction between the adjustment of the moment of inertia J to the active power and the rate of change of frequency of the system,that is,the dynamic adjustment performance of power and frequency cannot be considered;The influence of the self-synchronization control parameters and the voltage tracking mechanism of the virtual synchronous machine are also analyzed.In view of the above contradiction of the fixed moment of inertia,the relationship between the moment of inertia and the virtual inertia power is discussed,and the expressions of power and energy constraints of the energy storage system configured by the virtual synchronous machine are obtained;According to the influence of the moment of inertia on the dynamic regulation performance of the power and frequency of the system analyzed in Chapter 3,and combined with the relationship between the moment of inertia and the rate of frequency change,a virtual synchronous machine control with adaptive moment of inertia is proposed.Finally,the dynamic characteristics of the process of self synchronization,power output,frequency modulation and voltage regulation,the influence of control parameters and the proposed adaptive control of moment of inertia are verified by simulation,and the simulation results are consistent with the theoretical analysis;the experimental platform of small power virtual synchronous machine is built,and the experimental results further confirm the correctness of the theoretical analysis and simulation results.