A joint frequency modulation control strategy to improve the frequency of AC and DC grid-connected systems in wind farms

Abstract

The invention discloses a combined frequency modulation control strategy for improving the frequency of the AC-DC grid-connected system of a wind farm, and proposes a method for jointly participating in system frequency regulation with energy storage and flexible DC additional control to improve the frequency of the main grid: first, the flexible DC converter at the wind farm Add the flexible DC frequency additional control based on the frequency change of the wind farm to the flow station, and use the large transmission power of the flexible DC transmission and the characteristics of short-term overload operation to give priority to improving the frequency characteristics of the wind farm; The inverter is connected in parallel on the DC line between the wind farm and the main grid to compensate for the frequency deterioration effect of the additional DC control on the wind farm side on the main grid. The invention gives priority to improving the frequency characteristics of the wind farm, ensures the safe operation of the wind farm, and simultaneously improves the frequency characteristics of the main network.

Description

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

AI Technical Summary

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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