Joint frequency modulation control strategy for improving frequency of AC/DC grid-connected system in wind power plant

Abstract

The invention discloses a joint frequency modulation control strategy for improving a frequency of an AC / DC grid-connected system in a wind power plant. The joint frequency modulation control strategyproposes a method employing energy storage and flexible DC additional control to participate in system frequency adjustment for improving main grid frequency, and comprises the steps of: firstly, adding flexible DC frequency additional control based on wind power plant frequency variation into a flexible DC converter station at the wind power plant side, and preferentially improving the frequencyproperty of the wind power plant by utilizing the features of high transmission power and capability of short-time overload operation of flexible DC power transmission; and secondly, parallelly connecting an energy storage system on a DC line between the wind power plate and a main grid by means of a current converter, and compensating for the frequency deterioration effect of the DC additional control at the wind power plant on the main grid. The joint frequency modulation control strategy preferentially improves the frequency properties of the wind power plant, ensures the safe operation ofthe wind power plant, and improves the frequency properties of the main grid.

Description

technical field [0001] The invention relates to the technical field of power electronics, in particular to a combined frequency modulation control strategy for improving the frequency of an AC / DC grid-connected system of a wind farm. Background technique [0002] With the increasing demand for new energy and the increasing scale of wind farms, the transmission capacity of the original AC lines can no longer meet the grid-connected requirements of wind farms. In order to improve the transmission capacity of the wind farm, the AC-DC parallel grid-connected mode based on VSC-HVDC (flexible direct current transmission) can be used to replace the original AC-DC grid-connected mode. The structure of AC and DC grid-connected system of wind farm is as follows: figure 1 as shown, figure 1 WFVSC (wind farm side voltage source converter) is the wind farm side converter station, and GSVSC (grid side voltage source converter) is the main grid side converter station. [0003] Consideri...

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Problems solved by technology

[0027] Among the above three technical solutions, measure 1 can only improve the frequency status of the main grid and improve the frequency stability of the main grid; measure 2 can only improve the frequency status of the wind farm side, and when the power imbalance of the wind farm occurs, the main grid needs to pass through the DC line Provide power support to the wind farm, and at the same time, the power difference of the wind farm can be transmitted to the main grid along the AC line. Due to the above effects, the power difference of the main grid may be too large, resulting in frequency instability; although measure 3 can recover in the initial stage of the wind farm power disturbance Power balance, suppressing frequency fluctuations of wind farms and main grid. However, compared with the large transmission power and short-term overload capacity of DC lines, the power and capacity of energy storage components are limited. When the wind farm at the sending end has too much power difference, The energy storage element cannot achieve the ideal effect of absorbing excess energy or releasing enough energy, which may still cause frequency instability of the wind farm and wind turbine off-grid

[0028] There are currently no control measures utilizing joint frequency regulation of wind farms and energy storage systems

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