Coordinated frequency modulation control method and system for ultra-high voltage direct current transmission system

Abstract

The invention relates to a coordinated frequency modulation control method and system for an ultra-high voltage direct current transmission system. The method is characterized by comprising the following steps of (1) determining a running curve cluster of a wind turbine group and selecting a plurality of working points belonging to a SOPPT curve in the running curve cluster, (2) obtaining a working curve corresponding to the no consideration of an operating speed and a power limit of a wind generation set, (3) determine an SOPPT running curve and an MPPT curve of the wind generation set, (4) determining a power command of the wind generation set such that the wind generation set runs according to the corresponding running curve, (5) allowing a transmitting end converter station of the ultra-high voltage direct current transmission system to work in a power control mode and a receiving end converter station of the ultra-high voltage direct current transmission system to work in a constant direct current voltage control mode, and (6) adjusting the transmission power of the ultra-high voltage direct current transmission system through droop control links of the transmitting end converter station and the receiving end converter station. The method and the system can be widely applied in the field of a cooperative control method for a wind farm and the ultra-high voltage direct current transmission system.

Description

technical field [0001] The invention relates to a method and system for coordinated frequency modulation control of an ultra-high voltage direct current transmission system, and belongs to the field of coordinated control methods for a wind farm and an ultra-high voltage direct current transmission system. Background technique [0002] In order to realize the long-distance transmission of large-scale wind energy, China has established several UHV DC transmission corridors. However, wind power generation equipment based on power electronic converters and UHVDC (High Voltage Direct Current, HVDC) transmission systems usually work in power control mode and do not respond to grid frequency changes. With the continuous improvement of wind power penetration, wind power generation systems replace traditional synchronous generators and are connected to the power grid on a large scale through UHV DC transmission systems, which will lead to a reduction in the equivalent inertia of the...

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Problems solved by technology

[0004] However, whether it is the virtual inertia control method or the primary frequency modulation control method, the existing methods have shortcomings: 1) The frequency control of wind turbines based on the optimization method has high computational complexity, and it is difficult to guarantee real-time performance. Accurate wind speed information, so the practical application of this method is difficult and the robustness is poor

2) Although the virtual inertia control method based on the df / dt feedforward link is simple and efficient, there is interactive coupling between the original control loop of the wind turbine and the frequency support control loop, and the adjustment effect of the original control loop will weaken the frequency modulation effect of the frequency support control loop

In addition, this method is difficult to solve the problem of continuous reduction of wind power captured by wind turbines during the inertia support process, which may introduce secondary disturbances to the power grid, resulting in a secondary drop in power grid frequency

3) The primary frequency modulation control method based on the steady-state frequency deviation, because the wind is intermittent, it is difficult to adjust the frequency modulation control loop coefficient according to the frequency deviation, and the method of variable coefficient will increase the complexity of the control algorithm

The method of curve switching can alleviate the above problems, but there are problems such as fixed operation curve form, the need to latch the fan speed value at the moment the grid frequency drops, and the inability to improve the dynamic and static indicators of the grid frequency at the same time.

4) For the UHV DC transmission system, the existing methods are based on the communication between the sending and receiving end converter stations to realize the mutual support of the frequency of the sending and receiving end power grids, without considering the transmission and receiving end commutation without communication Cooperative Control Problem Between Stations

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