Method for judging severity of grid voltage dip

Abstract

A method for judging the severity of grid voltage dip comprises: detecting grid line voltage instantaneous value to calculate grid line voltage effective value; calculating the amplitude dip severity of each line voltage and the unbalance of the grid voltage according to the grid line voltage effective value and the grid line voltage rating effective value; fitting grid voltage unbalance curve through referring to the low voltage ride through standard curve A of a wind generating set according to the unbalance of the grid voltage; when the grid line voltage amplitude is larger than or equal to the grid voltage amplitude of the curve A, and the grid line voltage unbalance is smaller than or equal to the grid line voltage unbalance of a grid voltage unbalance curve B, the wind generating set needs uninterrupted running; and when the grid line voltage amplitude is less than the grid voltage amplitude of the curve A or the grid line voltage unbalance is larger than the grid voltage unbalance of the curve B, the wind generating set can be allowed to be cut out. The invention avoids the difficulty of judging the dip form of grid voltage, and can realize that the wind generating set meets the automatic control of the grid fault through capacity standard.

Description

technical field [0001] The invention relates to a method for evaluating grid voltage, more specifically, a method for judging the severity of grid voltage drop. Background technique [0002] With the rapid growth of wind power installed capacity, the proportion of its power generation capacity in the grid is also increasing. If the wind power generating set goes off-grid and shuts down when the power grid fails, it will not be able to provide frequency and voltage support to the power grid, which will be very detrimental to the safe operation of the power grid. Therefore, countries around the world have successively introduced a series of operating specifications for wind turbines, including grid fault ride-through capability, that is, when the grid experiences a short-term drop, wind turbines should remain connected to the grid and provide certain reactive power support during the fault period. , to help the grid recover as soon as possible. [0003] In order to ensure th...

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Problems solved by technology

For example, when a single-phase drop fault occurs on the 35KV bus, what is seen on the 690V bus is a two-phase phase-to-phase short-circuit fault. Therefore, the voltage drop detected at the wind turbine end is often not the real situation of the grid voltage drop;

[0011] 3. The low-voltage ride-through standard curve of wind turbines shows the phase voltage drop curve of the grid, but the actual wind turbine system uses a three-phase three-wire system without a neutral line, that is, the wind turbine system finally detects the grid line voltage. In the case of the neutral line reference, infinitely many solutions can be obtained by calculating the phase voltage through the line voltage, which brings great difficulties to the final judgment of the grid voltage drop form

[0012] In the above-mentioned prior art, due to the difficulty in judging the drop form of the grid voltage, it is very difficult for the wind turbine to meet the grid fault ride-through capability standard of the wind turbine.

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