Low-voltage ride-through method of wind power flexible direct-current output system

Abstract

The invention discloses a low-voltage ride-through method of a wind power flexible direct-current output system. Firstly, for a positive and negative sequence double-synchronous rotation coordinate system current controller adopted by a total-power or partial-power transformation type power supply, a steady-state running current expression suitable for a low-voltage ride-through condition of the wind power flexible direct-current output system is designed, and based on this, a total-power or partial-power transformation type power supply model is built; according to the difference between thewind power flexible direct-current output system and a traditional power transmission system, a flexible direct-current power transmission system control strategy suitable for the wind power flexibledirect-current output system is designed; and then, for the problems that under the condition that the wind power flexible direct-current output system has a serious line fault, a voltage of a direct-current line is continuously increased, the line is damaged, and a power electronic device of an MMC is unsafe, a low-voltage ride-through stabilizing circuit is used for realizing low-voltage ride-through. By applying the method, the flexible direct-current transmission line can achieve a fault isolation effect, so that the running stability of the wind power flexible direct-current output systemis improved.

Description

technical field [0001] The invention relates to the technical field of grid-connected new energy power generation, in particular to a low-voltage ride-through method for a wind power flexible DC transmission system. Background technique [0002] At present, in order to solve the world's over-reliance on fossil energy, environmental pollution, energy resource shortage and other problems, the power generation technology using renewable energy such as wind energy has been developed rapidly. With the maturity of wind power technology and the strong support of policies, the development of wind farms has the characteristics of large scale and far away from the load center. These large-scale wind power cannot be accommodated locally, so they need to be transported to the load center through the transmission grid over long distances. In the past, most of the substations were AC convergence. However, the current flexible DC transmission technology is mature. Compared with AC transmi...

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Problems solved by technology

[0003] However, when a fault occurs on the AC side, the output power capability of the grid-side converter is reduced, the output power of the wind farm remains unchanged, and excess power is accumulated on the DC transmission line, resulting in an increase in the DC voltage.

The low-voltage ride-through strategy of the existing technology focuses on the coordinated control of MMC converters on the wind farm side of wind power and flexible direct current transmission lines. Although the method of increasing frequency or reducing voltage does not require additional equipment, it is too large Frequency or voltage changes within a certain range may have a great impact on the wind turbine, and even cause the shutdown action, which cannot completely solve the problem of the power difference between the two ends

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