Influential Mechanism Of Virtual Inertia Delay Of Wind Power And Its Substitutability Research

Vigorously developing wind power plays a vital role in responding to the energy crisis and climate deterioration,and complying with the implementation of the "carbon peak·carbon neutral" goal.However,wind turbine generators(WTG)are connected to the grid through power electronic devices,and the rotor speed is decoupled from the grid frequency,which makes it unable to spontaneously respond to the system frequency changes like a synchronous machine(SG).As the penetration rate of wind power increases,the inertia level of the grid gradually decreases,leading to severe challenges to the frequency safety of the grid.For this reason,both Chinese and foreign power grid operation guidelines stipulate that WTG in grid-connected operation shall have the capacity of inertia response and primary frequency regulation.However,when WTG adopts the virtual inertia control to participate in grid frequency regulation,its essence is the fast power response with time delay,with inherent frequency measurement,communication and response links,and has inherent defects such as high frequency measurement accuracy requirements,large delay,amplification measurement error of frequency differential link,which leads to its poor reliability.However,there is currently limited research on the delay characteristics of virtual inertia,and there are many problems that urgently need to be solved.It mainly includes the following two aspects:1)The existing frequency response model does not take into account the virtual inertia delay,resulting in significant errors between the model analysis results and the actual situation.2)The mechanism of the impact of delay on system frequency control is not clear,and the inherent defect of virtual inertia leads to poor reliability.In response to the above issues,the specific research contents of this paper are as follows:In response to the problem of significant errors in the model analysis results caused by the existing system frequency response model not taking into account the virtual inertia delay.This paper based on the traditional power system frequency response model,considering the frequency regulation characteristics of WTG,and focuses on the delay characteristics of wind power virtual inertia power response,then an aggregated equivalent single machine frequency response model considering the virtual inertia delay characteristics of WTG is established.Firstly,the frequency regulation characteristics of WTG are modeled and analyzed.The external characteristics of WTG during frequency regulation are approximately equivalent to the combination of virtual inertia,droop control,and delay link.Then,considering the difference of frequency regulation characteristics between each generator unit in the power system,a multi machine frequency response model considering the differences in frequency regulation characteristics between units was established based on the traditional average system frequency response model.Further,based on the weighted equivalence method,the multi machine frequency response is aggregated and equivalent to a single machine frequency response.Finally,an aggregated equivalent single machine frequency response model considering the virtual inertia delay characteristics of wind power was established.In response to the problem of the mechanism of the impact of wind power virtual inertia delay on the system frequency control is not clear,and there are many inherent defects that lead to poor reliability.This paper studies the mechanism of the impact of delay on system frequency control and WTG power response,and analyzes that the droop control has higher reliability compared with the virtual inertia control,and accordingly proposes to use the droop control to replace the virtual inertia control.Firstly,based on the aggregated equivalent single machine frequency response model considering the virtual inertia delay characteristics of wind power established above,the Routh approximation method is used to reduce the order of the model and obtain the analytical expression of the nadir of the system frequency,and the influence mechanism of the delay is analyzed through the expression.Then,the system frequency response model of wind power frequency regulation system using only droop control is solved analytically,and the droop control coefficient setting method with the same frequency regulation effect as virtual inertia and droop control is given under the nadir of the frequency index.Finally,under the setting of droop control parameters,key indicators such as maximum frequency change rate and steady-state frequency were compared between the two control methods.It was concluded that properly increasing the droop control coefficient can achieve the purpose of replacing the virtual inertia and achieve better frequency regulation effect than the virtual inertia and droop control.