Analysis Of Voltage Stability Of Receiving-end Power Grid Adapted To Photovoltaic And DC

In order to effectively solve the problem of the imbalance in the geographical distribution of energy and load in my country,multiple large-capacity DC transmission lines have been put into operation one after another to transmit electric energy from the west to the Central China power grid.As the DC drop point is connected to a large number of photovoltaic power stations in the vicinity,large-capacity DC transmission systems and large-scale photovoltaic power stations are simultaneously connected to the Central China Power Grid.The most common commutation failure of the DC transmission system will cause the voltage on the inverter side to drop significantly,causing unipolar or bipolar blocking of the converter station,causing problems such as disconnection of the interlocking unit and load rejection,and affecting the stability of the grid voltage.The photovoltaic power station installed near the DC drop point has dynamic reactive power support capability,which provides a new idea for suppressing the continuous commutation failure of the DC transmission system.Consider the coupling relationship between the photovoltaic power station and the DC transmission system,analyze the impact of photovoltaic power station on the DC commutation failure,and realize the output reactive power suppression of the photovoltaic power station.The continuous commutation failure of the DC transmission system is of far-reaching significance for the safe and stable development of the power system.This dissertation studies the security and stability of photovoltaic and DC connected to the same receiving-end power grid from the following three aspects:(1)Establish models of photovoltaic power plants and DC transmission systems,and analyze the coupling relationship between the two connected to the same receiving end grid.Establish equivalent models of photovoltaic power plants and DC transmission systems,respectively analyze the power output characteristics of photovoltaic power plants in different modes and the dynamic output characteristics of DC lines;build models on the PSCAD/EMTDC and PSDBPA simulation platforms to verify the performance of the above components Transient and steadystate characteristics,and analyze the interaction between photovoltaic and DC transmission systems.(2)Analyze the impact of different proportions of photovoltaics connected to the receiving end grid on the commutation failure of the DC transmission system and the strength of the receiving end grid.When the AC system is subject to large disturbances and the DC transmission system commutation failure,analyze the reactive power demand of the DC transmission system during the failure;on the basis of the established simulation model,introduce the commutation failure immunity factor as the evaluation index to analyze the photovoltaic power station access Impact on the ability of the DC transmission system to withstand commutation failure;analyze the impact of different proportions of photovoltaic power plants on the recovery characteristics of the DC transmission system after a failure.(3)Propose a reactive power compensation strategy for photovoltaic inverters to suppress DC continuous commutation failure.Refer to the commutation bus voltage and the DC inverter side arc extinguishing angle,adjust the active power and reactive power of the photovoltaic output,increase the reactive output of the photovoltaic inverter when a fault occurs,and achieve the purpose of suppressing the continuous commutation failure of the DC transmission system;The actual power grid and standard test system verify the proposed strategy and verify the effectiveness of the proposed method.Based on the above background and needs,while making full use of the flexible control methods of photovoltaic power plants and DC transmission,it also comprehensively utilizes the characteristics of photovoltaic inverters and DC transmission systems from the perspective of maintaining voltage stability,effectively improving the dynamic operating characteristics of the system and inhibiting DC transmission The continuous commutation failure of the system is of great significance to promote the safe and economic coordinated development of the receiving end power grid,and provides important reference value for the safe and stable operation of actual projects.