Unit frequency and voltage control method suitable for island operation of sending end of high-voltage direct-current system

Abstract

The invention discloses a unit frequency and voltage control method suitable for the island operation of the sending-end of a high-voltage direct-current system and particularly relates to a sending-end hydraulic power plant unit frequency and voltage optimization control method suitable for the island operation of the sending end of the high-voltage direct-current transmission system. According to the unit frequency and voltage control method suitable for the island operation of the sending end of the high-voltage direct-current transmission system, when the sending end of the high-voltage direct-current transmission system actively enters or passively jumps into island operation, control logic and parameter optimization are carried out on a speed regulation system, an excitation system and a PSS device. According to the prior art, when the sending end of a high-voltage direct-current transmission system actively enters or passively jumps into island operation, an island system is small in rotational inertia and insufficient in short-circuit capacity, and problems such as high-frequency, overvoltage or ultralow-frequency oscillation exist when serious faults such as direct-currentlocking occur, and as a result, the safe operation of the island system and equipment is threatened. With the method of the invention adopted, high-frequency and over-low-voltage suppression, ultralow-frequency oscillation of the island system and other stability problems are solved in a balanced manner, and the safe and stable operation of the island system is effectively guaranteed.

Description

technical field [0001] The invention relates to a unit frequency and voltage control method suitable for high-voltage direct current sending end island operation, in particular to an optimal control method for hydropower unit frequency and voltage suitable for high-voltage direct current sending end island operation. Background technique [0002] In recent years, the DC transmission system has been widely used in my country and around the world due to its advantages of large transmission capacity and long distance. However, the AC grid structure in the vicinity of hydropower bases in western my country is often relatively weak, and the connection between the DC sending end system and the main network is weak. In order to reduce the impact of DC blocking on the system and improve system stability, there are active arrangements for island operation at the sending end of the large-capacity DC system. Or passively jump into an island mode of operation. When the DC sending end op...

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Problems solved by technology

[0004] (2) Due to the small moment of inertia of the unit, the dynamic damping provided by the island system is insufficient. In particular, due to the influence of the inertial time constant (TW) of the water turbine, it is easy to show insufficient damping in the ultra-low frequency band (generally 0.03Hz-0.1Hz) and may even provide Negative damping, and DC itself, as a rigid load, cannot provide damping for system disturbances. Therefore, island system hydroelectric units are prone to excite ultra-low frequency oscillations

During the commissioning or operation of actual DC islands in China, ultra-low frequency oscillation problems also occurred many times, threatening the safe operation of the island system;

[0005] (3) Island system overvoltage problem

When the DC sending end is running in an isolated island, DC unipolar blocking, unit tripping, etc. will cause large frequency fluctuations. According to the basic principles of the dual-input PSS2A and PSS2B devices widely used in China, the increase in frequency will cause PSS (Power System Stabilizer ) positive output, the frequency drop will cause the reverse output of PSS, which will lead to large fluctuations in the voltage in the island system; at the same time, once the DC bipolar blocking occurs in the island system, due to the excess of a large number of filters, serious overvoltage will inevitably occur. On the power plant side, the measures of quickly switching all the filters are generally taken to control the overvoltage level, but for the power plant side unit, the large and rapid increase in frequency will inevitably lead to the positive output of the PSS device, and the power plant will emit a large amount of reactive power, further deteriorating the island system overvoltage Level

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