Research On Virtual Synchronous Generator Control Strategy Based On State Of Charge Of Energy Storage

In recent years,the penetration of distributed generation in power system is increasing,which brings a lot of challenges to the stability of power system.Virtual synchronous generator(VSG)technology is one of the representatives,and thus by academia and the industry’s attention,and has formed a research focus.Through the electromagnetic equation,motion equation and the frequency and voltage controller characteristic simulation of synchronous generator,the distributed generation can have similar synchronous generator function.And how to meet the storage requirements of the state of charge(SOC)according to the different types of energy storage(power type,energy type)and application(grid connection,diesel connection,multi-machine parallel,etc.)of VSG VSG control strategy,which is one of the key technology.This paper mainly focuses on the VSG control strategy based on energy storage SOC control,including SOC control in grid-connected mode,SOC and frequency coordination control in diesel generator set(DGS)connected mode and SOC balance control in multi VSG paralled mode.This paper mainly research and innovation are summarized as follows:(1)The basic control principle of VSG is analyzed,and the VSG is decomposed into two parts;the energy storage unit of the energy supply part of the analog synchronous generator and the inverter unit which simulates the mechanical characteristics and electrical characteristics of the synchronous generator according to the function.A mathematical model is established for the inverter unit,and the parameters of the power control loop and the voltage control loop are designed respectively.A mathematical model of typical energy storage devices such as batteries and supercapacitors is established for the energy storage unit,and the parameters of the control system are designed according to the converter topology of the energy storage unit.(2)The influence of VSG control parameters on SOC control is analyzed,and a VSG SOC control algorithm based on time fuel optimal control theory is proposed to solve the shortcomings of SOC control bias and difficult to control VSG output frequency.The third order VSG control matrix is transformed into the second order integral standard,which satisfies the analytic condition.The SOC optimal control trajectory is obtained by phase plane calculation,which effectively improves the control precision of SOC.At the same time,it can limit the maximum deviation of VSG output frequency.The influence of the time weighting coefficient on the control response speed and the power quality corresponding to the frequency deviation in the control process is analyzed,(3)The mathematical model of DGS and the control requirements of SOC are analyzed,a VSG control algorithm including SOC control and frequency control is proposed to meet the influence of SOC change and system frequency change during load change.In order to achieve SOC control and frequency control between the coordination,the introduction of the concept of weight coefficient.The small signal model of VSG system is established,and the influence of different weighting coefficients on frequency regulation and SOC regulation is analyzed.Aiming at the different requirements of SOC for different energy storage,a variable weight coefficient design scheme is proposed to improve the storage capacity of the energy storage unit range.(4)Aiming at the problem that the traditional frequency control can not achieve the SOC balance between multiple VSGs,the two schemes of SOC equalization are improved and analyzed by improving the frequency curve.On this basis,a comprehensive SOC equilibrium control strategy for VSG is proposed.The design requirements of the control parameters are analyzed from the angle of load capacity limit,steady frequency frequency deviation and system stability.Aiming at the shortcomings of the current research on the lack of quantitative analysis of SOC equilibrium process,the time-domain analytical formula of the whole SOC equilibrium process is deduced by establishing the mathematical model of the two-load system.The validity of the SOC equilibrium strategy is verified from the quantitative analysis.(5)The experimental platform including multi-VSG and DGS is set up.The hardware and software design of the energy storage unit simulator is introduced in detail,and the control schemes of the above analysis are experimentally verified.