Research On Frequency Emergency Controlstrategy Based On Pumped Storage After Receiving-end Power Grid Failure

With the continuous development of power system technology,compared with the traditional power grid,the power grids in most parts of China can be connected to each other.The power grid has spread to many harsh and remote areas in China,and can be transmitted by UHV and contain The direction of large-scale wind power development.If there is a problem with the contact line that connects to various regions and cannot work normally,it will cause a significant reduction in the frequency of the power grid.Because large-scale wind power has the characteristics of weak frequency modulation and weak inertia,it will obviously weaken the frequency distribution of the power grid.However,in recent years,wind power has been spreading throughout the region.The frequency of the originally high-end receiving power grid has gradually decreased and increased.Stability,if bipolar blocking occurs on the large-capacity UHV DC line from the transmission-end power grid to the receiving-end power grid,the frequency stability of the power grid will be greatly weakened,and in extreme cases,a frequency dip will occur,resulting in a frequency breakdown of the power grid risks of.Therefore,it is necessary to study countermeasures and control measures to deal with the emergency frequency decrease.When the frequency of the power grid drops significantly,cutting off the load and readjusting the frequency are currently the most commonly used emergency measures in the power sector,but the biggest drawback of this emergency measure is the loss of power system load.The loss of load is not economical.Pumped energy storage is currently mainly generated by storing water at the peaks and valleys of electric loads,so it has the characteristics of large adjustment capacity and fast response speed,and is also an emergency measure.Through a large-scale survey and analysis,this paper summarizes the pros and cons of changes in the frequency of the power grid in the region as wind power continues to spread throughout the region in recent years.For some of the disadvantages,it also proposes emergency plans through pumped storage.1)The static frequency characteristics of large-scale wind power systems are studied.The frequency modulation characteristics of direct-drive wind turbines are studied,especially for wind turbines that can be frequency-modulated at one time.The calculation method of the power-frequency coefficient of wind turbines is proposed and the static frequency characteristics of the system are described.For the nonlinear effect of large-scale power deficit on the power-frequency coefficient,this paper proposes an average weighting algorithm based on the principle of probability statistics.2)The dynamic frequency characteristics of large-scale wind power systems are studied.This paper expounds its influence on the dynamic frequency characteristics of the power grid by investigating and analyzing the inertia of the direct-drive wind turbine.According to the difference between the direct and indirect grid connection of the wind turbine,it is divided into the type of direct grid connection and the type of grid connection through power electronic devices.And for the situation that the fan connected to the grid through the power electronic device can not be accurately judged as gravitational or inertial force,it is called the concept of "equivalent inertia" and the corresponding calculation method is proposed.The comprehensive system power-frequency coefficient and overall inertia analysis have shown that the frequency of the power grid has been changing because of the continuous spread of wind power.3)The characteristics of working condition conversion of pumped storage units are studied.The detailed process and principles of pumped storage units generating electricity by storing water at peaks and troughs of electric load are expounded and converted into mathematical models.The model is mainly divided into hydraulic machinery part and generator part.The former mainly works by establishing a full-characteristic curve model and the guide vane closing model within the time range,while the latter mainly divides into five different levels to propose a new type of identification for the model parameters of the conversion process of different working conditions.The algorithm can be compared with the power plant nameplate parameters to verify the accuracy of the algorithm.Finally,the method of simulating the working condition conversion process of pumped storage unit in PSASP software is given.Finally,by cutting off the load and changing the frequency value,it is possible to properly deal with the problem of the frequency drop of the power grid throughout the wind power region.The most important part of this strategy is to find the optimal frequency trajectory.By drawing the specified frequency curve and the actual frequency curve of the power grid work,the optimal frequency trajectory is found by the overlapping area of the two,and the frequency fluctuation range is used as the limiting condition.Use the external penalty function method to solve.The effect of different generators on this measure in different permeability conversions is described.