| With the continuous development of wind power in my country,the power transmission mode of wind-thermal-bundled AC-DC hybrid transmission is the main form of power transmission from wind power bases in remote areas.This method not only completes the major problem of cross-regional transmission of a large number of power resources to the load center,but also solves various transient stability problems caused by the independent transmission of wind power.At the same time,the UHV DC transmission mode can transmit electric energy with long distance and large capacity,and the cost of the DC transmission line is lower than that of the AC line,which greatly improves the economy of power transmission.However,there are intricate influencing factors in the wind-thermal-bundled system,so it is urgent to study the key factors affecting the transient stability,which will play a crucial role in the future development of my country’s energy strategy.Aiming at the transient power-angle stability of the wind-thermal-bundled AC-DC hybrid delivery system,an equivalent model of the wind-fire bundling system delivery system is established.Based on the electromagnetic power analytical expression of the synchronous machine of the single-ended power transmission system,the change of the power-angle curve of the wind power connected to the synchronous machine is analyzed from three angles,and the simulation verification is carried out according to the actual system.Finally,a safety control strategy is proposed.First,refer to the instruction manual of the PSD-BPA software stabilization program,and introduce the mathematical models of each part of the typical wind-thermal-bundled system in detail.Then,based on the mathematical model of each branch,the simulation model of the wind-thermal-bundled system was built,and its equivalent circuit was introduced in detail;Based on the low-voltage ride-through characteristics and DC transmission transient characteristics of DFIG,the changes of active power and reactive power before and after the fault are analyzed;Then,based on the electromagnetic power analytical expression of the synchronous machine of the single-ended power transmission system,the influence of the connection method of the wind power equivalent output replacing the output of the synchronous machine on the initial power angle of the synchronous machine is analyzed,and compared with the negative load output,according to the equal-area-criterion,the influence of the active power slow recovery characteristics and reactive power compensation characteristics of the wind turbines on the transient power angle stability of the synchronous machine after the fault is cleared is analyzed compared with the negative load connection,and the accuracy of the theory is verified by simulation.Secondly,the simulation and verification of the power transmission system of Ximeng Power Grid is carried out.Under the control of AC or DC faults,from different angles,the simulation analyzes the influence mechanism of the wind power simultaneity rate on the transient stability of the system under different faults.And through the comparison of the influence of the two faults on the transient stability of the system,the coupling characteristics of the AC-DC hybrid system are analyzed.Finally,the influence of thermal power cut off and wind power cut off on the transient stability of the system is analyzed theoretically.After the system fails,several safety control and cutting strategies are adopted,and the influence on the transient stability of the system is verified by simulation comparison.And for Ximeng wind-thermal-bundled AC and DC weak sending system,an applicable safety control and cutting machine measure is proposed. |
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