A wind field multi-terminal flexible direct control method and system capable of actively supporting grid frequency

Abstract

The invention provides a wind field multi-terminal flexible DC control method capable of actively supporting the frequency of a power grid, and also provides a system for executing the method. The method and the system comprise the control of a receiving-end converter station and the control of a sending-end converter station. Phase-locked-loop-free autonomous power grid synchronous control is realized at the receiving-end converter station by utilizing inherent dynamic characteristics of a DC bus equivalent capacitor, so that the receiving-end converter station reflects an AC power grid as avoltage source, and the problem of resonance of connection into a weak power grid is solved. A virtual resistor is added to the DC side, so that the DC side has a droop characteristic to coordinate power distribution among multiple receiving-end converter stations. In addition, the DC side voltage of the receiving-end converter station can automatically respond to the frequency changes of the power grid. On one hand, DC system power flow can be automatically adjusted, and power can be called from other power grids to achieve a primary frequency modulation function. On the other hand, the DC bus voltage can be linked with the frequency deviation of the power grid, and the frequency change information of the power grid can be transmitted to a wind field side through the sending-end converterstation to assist the wind field in realizing inertia response.

Description

technical field [0001] The present invention relates to the technical field of control of multi-terminal flexible direct current transmission systems, in particular to a method and system for multi-terminal flexible direct current control of a wind field that can actively support the frequency of the power grid, which is used to realize the access of wind farms with active frequency response to the power grid. The multi-terminal flexible DC transmission system applied to the grid connection of long-distance offshore wind farms, including the active / reactive power control strategy of the receiving-end converter station and the sending-end converter station. Background technique [0002] The basic topology of the multi-terminal flexible DC transmission system for offshore wind farms figure 1 , the system is mainly composed of sending-end system (wind farm group), sending-end converter station, DC overhead line, DC circuit breaker, current-limiting reactor, receiving-end conver...

AI Technical Summary

Problems solved by technology

However, the above studies are all aimed at point-to-point wind farms-flexible direct grid connection, and the working mode of the converter station is often constant power or constant voltage control. When applied to the wind power-multi-terminal flexible direct grid connection system, the Only master-slave control can be used for coordination. This control method relies heavily on communication reliability, and wind power fluctuations need to be fully borne by the master station, which is not suitable for wind power transmission.

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