| According to China’s "carbon peak,carbon neutral" strategic goal and the future"Fourteenth Five-Year Plan" development plan,the new energy power generation technology represented by wind power and photovoltaic power generation has been developing continuously,the proportion of installed capacity of new energy stations has been rising,and China’s power system and power structure have undergone profound changes.However,considering that wind turbines are connected to the power grid through power electronic devices,their withstand voltage and current capacity are relatively weak.In order to prevent the devices from being damaged by excessive current in case of fault,wind turbines generally have the ability of low voltage ride through.After entering the low voltage ride through,the active power output of the wind turbine will generally be significantly reduced.This short-term power disturbance process will cause the near area power flow and voltage fluctuation,and in serious cases may cause the wind turbine to be disconnected from the grid in a chain manner,and the frequency will shift in a large range.In order to solve the above problems,this paper aims at the power system under large-scale wind power access,starting from the perspective of prevention and control,to suppress the short-term active impact caused by large-scale wind power low-voltage ride through,and ensure the frequency stability of the power system.Firstly,the equivalent direct-axis sub transient reactance equivalent model of grid-connected power supply and the low voltage ride through strategy of wind turbines are described,and the voltage problems directly caused by the wind turbines connected to the grid and the frequency problems indirectly caused by the wind turbines are analyzed.At the same time,the power system simulation model is built to verify the impact of large-scale wind power low voltage ride through on the frequency,and the main factors affecting the frequency response index are analyzed.Secondly,for the power system with large-scale wind power access,the optimal configuration strategy of condenser is proposed to suppress the active impact caused by wind power low voltage ride through.According to the node impedance matrix,the active impact index is proposed to measure the magnitude of the active impact caused by wind turbines;The dynamic voltage support performance of the condenser and the impact of the condenser connection on the active impact index are analyzed.The results show that the condenser can suppress the transmission of voltage drop in the power system to suppress the active impact,and then the optimal configuration strategy of the condenser is proposed.Then a simulation model is built to verify the proposed condenser optimal configuration strategy.The simulation results show that the access of the condenser can provide more dynamic reactive power support during the fault,raise the voltage of the wind turbine grid connection point,and then reduce the scale of the wind turbine entering the low voltage ride through,thus reducing the active impact caused by the low voltage ride through of the wind power,and maintaining the frequency stability of the power system in a safe and stable range,The frequency stability is guaranteed.Thirdly,aiming at the cooperative control of multiple types of reactive power sources in the power system,a reactive power source coordination strategy based on reactive power and voltage control zoning is proposed,the concepts of static reactive power source and dynamic reactive power source in the power system are defined,and the reactive power-voltage control zoning method is proposed according to the sensitivity matrix representing the electrical distance,the reactive power source node,and the distance evaluation function,realizing the spatial decoupling of reactive power source coordination;In order to realize the decoupling of reactive power resources in time,the reactive power dispatching master station is set in each reactive power zone,the dynamic reactive power and static reactive power capacity are monitored in real-time,and the dynamic reactive power is replaced in real-time by static reactive power.On this basis,the optimal switching scheme and optimal switching time of the capacitor/reactor bank are proposed.Finally,the simulation model is used to verify the above strategy,and the results show that the proposed strategy can provide more dynamic reactive power support to the power system,so as to raise the voltage during the fault,ensure the voltage level of the wind turbine grid connection point,and improve the voltage stability of the power system.Finally,in view of the security and stability of the power system under high permeability wind power,an auxiliary decision-making system considering the bearing capacity of new energy fault traversal is proposed.Firstly,based on the equivalent circuit of the doubly-fed induction generator,the range of active power and reactive power output under different voltages is derived,and the voltage-active power model during the fault period is established in combination with the reactive active support strategy of the wind turbine.Combining the model with the frequency response model,the voltage-active power-frequency mathematical model is finally established.Based on this mathematical model,an online auxiliary decision-making system for real-time evaluation of the permeability of wind turbines is proposed,which takes the low-frequency defense line of the power system as the constraint,and realizes the functions of screening the expected accidents and controlling the output of wind turbines.Finally,the function of the auxiliary decision-making system is verified by simulation.The results show that the auxiliary decision-making system can adjust the proportion of wind power in real-time according to the severity of the predicted accident,so as to avoid the cascading accident caused by the active impact caused by the large-scale wind power low voltage ride through,and ensure the frequency stability of the power system. |
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