A control method for improving the transient voltage of the inverter station of the DC transmission system

Abstract

The invention provides a control method for improving transient voltage of a direct-current power transmission system inversion station. The control method includes: mounting a unified power flow controller in an alternating-current station adjacent to the direct-current power transmission system inversion station; connecting the unified power flow controller and a direct-current power transmission system into a same alternating-current system. By adopting the structure, after the circumstance that alternating-current voltage of the direct-current power transmission system inversion station is lowered is detected, the control mode of the unified power flow controller is quickly switched into an injecting voltage control mode, and improving of voltage connected into a bus by the unified power flow controller is controlled, so that voltage connected into an alternating-current bus by the direct-current power transmission system inversion station is improved, and probability of phase change failure of the direct-current power transmission system is lowered. Compared with other reactive compensation and voltage control devices, the structure has higher economic efficiency. The control method has remarkable effect on improving the transient voltage of the direct-current power transmission system inversion station.

Description

technical field [0001] The invention relates to an AC-DC hybrid power transmission technology, in particular to a control method for increasing the transient voltage of an inverter station in a DC power transmission system. Background technique [0002] The thyristor-based grid commutation HVDC transmission system has large transmission capacity, low line cost, strong asynchronous networking capability, and has great advantages in long-distance large-capacity transmission and large-area networking. The high-density connection of the DC transmission system to the AC grid makes the interaction between the AC and DC systems increasingly complex, and poses a huge challenge to the safe and stable operation of the grid. Commutation failures in high-power DC systems are relatively common, mostly caused by faults in the AC system at the receiving end. During the period of commutation failure, the DC power drops sharply, and the synchronous generator of the DC transmission grid acce...

AI Technical Summary

Problems solved by technology

During the period of commutation failure, the DC power drops sharply, and the synchronous generator of the DC transmission grid accelerates. If the commutation failure lasts for a short time, the DC power can recover quickly, which has little impact on the stable operation of the system, but continuous commutation failures will affect the stability of the system. The influence of power is relatively serious, and the repeated impact of continuous commutation failure may cause the relative power angle instability of the sending unit and the disconnection of important AC connection sections

[0003] There are many reasons for commutation failure, but when the thyristor and its trigger system are working normally, the main reason for commutation failure is the grid voltage drop or fluctuation caused by the failure of the receiving end grid

At present, the application and published patents of DC power transmission projects mainly suppress commutation failure by optimizing the control strategy of DC power transmission. Most of them are to increase the turn-off angle or reduce the DC current, which can be used as an auxiliary preventive method for commutation failure. But it is impossible to fundamentally avoid the occurrence of commutation failure

[0004] In recent years, some people have studied the installation of large-capacity STATCOM and large-capacity condensers near the inverter station of the DC transmission system to compensate the reactive power of the inverter station, and increase the voltage of the inverter station when the system fails, thereby reducing the commutation of the inverter station. The probability of failure, but this method is only suitable for the working condition of the light grid fault at the receiving end. When the grid voltage drop is serious, the reactive power capacity required to compensate the voltage drop is very large, and the existing reactive power compensation device cannot cope with it.

[0005] Therefore, it is necessary to study a structure and control method with a strong ability to improve the voltage efficiency of the system during a fault, so as to solve the problem that the existing reactive power compensation device cannot cope with the voltage drop when the power grid is severely faulted

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