| With the rapid development of AC / DC hybrid power grid and the expansion of new energy sources such as wind power and photovoltaic,the form of modern power grid is becoming more and more complex,and the operation mode has changed greatly.The traditional offline auxiliary decision-making has been difficult to provide certain technical support for the grid.At the same time,the random volatility of wind power,photovoltaic and other new energy sources will bring great challenges to the security and stability of the grid,and even cause a large number of new energy out of the network,resulting in unnecessary economic losses.This thesis considers the security and stability of power system from the point of view of on-line decision-making,based on the wind,PV and thermal power coordinated optimization operation,this thesis studies the reactive voltage emergency control strategy of large-scale wind farm grid-connected system and the auxiliary decision-making of power supply system for transient power angle emergency control,and then presents an emergency control technology of power network which is based on the short-term forecast.The main work of this thesis is:(1)Based on the forecast information of wind power and PV power and the measured power,the space for emergency control measures is determined.With the goal of maximizing the output of wind power and PV,the conventional unit is preferentially controlled and a coordination and optimization model between conventional units and wind power photovoltaic is established.According to the short-term power forecast information of wind power and photovoltaic,wind power and photovoltaic power units are dynamically grouped to determine the active control strategies of each trend group.(2)A reactive power and voltage emergency control strategy for large-scale wind farm grid connected system is put forward based on dynamic reactive power compensation device SVC and SVG,shunt capacitor branch,controllable high resistance and wind power cutting and load removal.First,the basic principles of dynamic reactive power compensator(SVC and SVG)are analyzed,and the dynamic voltage response characteristics of the two are studied under the same reactive power capacity.Secondly,the additional SVC latching control under severe voltage drop and the coordinated control of SVC and SVG near the electrical distance are put forward to achieve voltage overshoot suppression in the process of voltage recovery.Finally,the effect of the action sequence of the reactive power compensator on the voltage is analyzed,and the time series optimization emergency control measures under the fault of the wind farm are put forward.(3)This thesis presents a cutting strategy that considers the emergent conditions such aspower failure,power line overload,and damping ratio too low,to resume stable operation as soon as possible.Firstly,a practical method to calculate the amount of thermal power is proposed based on the method of transient energy function with stable power angle.Secondly,the variation characteristics of the system damping ratio and the corresponding characteristics of transient energy are analyzed when the proportion of wind turbine is increasing.Finally,considering the influence of the main line being overloaded and the high penetration rate of wind power on the strategy of transient cutting machine,an emergency control strategy of cutting out some of the wind power should be removed at the same time except for the necessary synchronous generator.Based on the standard test system and the actual example of wind power grid-connected system,the feasibility and practicability of the above algorithm are verified.The analysis methods and technical means mentioned in this thesis have important guiding significance in promoting the development of new energy sources and improving the operational economy and safety of new energy grids.At the same time,it can provide feasible online safety and stability emergency assistance decision-making for the actual project operation. |
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