A control method for reducing the probability of commutation failure in DC transmission

Abstract

The invention provides a control method for reducing the probability of direct current transmission commutation failure. A unified power flow controller is installed at an alternating current station adjacent to a direct current transmission system inverter station, and the unified power flow controller and a direct current transmission system are connected to the same alternating current system. By means of the above structure, after the alternating current voltage of the direct current transmission system inverter station is detected to decrease, the control mode of the unified power flow controller is quickly switched to an injection voltage control mode, and the voltage of the access bus of the unified power flow controller is controlled and increased, thus increasing the voltage of the access alternating current bus of the direct current transmission system inverter station and reducing the probability of commutation failure of the direct current transmission system. Compared with other reactive power compensation and voltage control devices, the structure is more economical, and the control method has a more significant effect on reducing the probability of direct current transmission commutation failure.

Description

technical field [0001] The invention relates to an alternating current and direct current hybrid transmission technology, in particular to a control method for reducing the commutation failure probability of direct current transmission. 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 transmiss...

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 voltage drop when the existing reactive power compensation device cannot cope with the serious fault of the power grid, so as to more effectively reduce the DC transmission commutation probability of failure

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