Offshore wind power uncontrolled rectification direct current power transmission system

Abstract

The invention relates to an offshore wind power uncontrolled rectification direct-current power transmission system which comprises an offshore wind power plant, an offshore converter station, a seabed direct-current submarine cable, an onshore converter station and an onshore power grid. The alternating current side of the offshore wind plant is connected with the alternating current side of the offshore converter station through an offshore alternating current bus, and the direct current side of the offshore converter station is connected with the direct current side of the onshore converter station through positive and negative pole direct current submarine cables; the alternating current side of the onshore converter station is connected with the onshore power grid; the offshore converter station comprises a full-bridge MMC unit and a diode uncontrolled rectification unit. The full-bridge MMC unit is used for providing a starting power supply or grid-connected voltage for the offshore wind power plant when the offshore wind power plant is black-started or runs normally; and the diode uncontrolled rectification unit is used for rectifying the electric energy output by the offshore wind plant and then transmitting the rectified electric energy to the onshore converter station. The method can be widely applied to the technical field of flexible direct current transmission.

Description

technical field [0001] The invention relates to an offshore wind power uncontrolled rectification direct current transmission system, which belongs to the technical field of flexible direct current transmission. Background technique [0002] Offshore wind power development is an important way to build a new type of power system in the future and achieve "carbon peaking and carbon neutrality". At present, the direct current transmission scheme is the only engineering implementation scheme to realize offshore wind power grid connection. However, the current direct current transmission scheme has the following problems: 1) The offshore converter station platform is bulky and expensive; 2) The converter valve generally adopts flexible direct current The inverter has a large number of sub-modules and expensive capacitors. Therefore, reducing the weight of offshore converter valves and offshore converter station platforms and improving the overall economics of HVDC transmission s...

AI Technical Summary

Problems solved by technology

At present, the direct current transmission scheme is the only engineering implementation scheme to realize offshore wind power grid connection. However, the current direct current transmission scheme has the following problems: 1) The offshore converter station platform is bulky and expensive; 2) The converter valve generally adopts flexible direct current Inverter, a large number of sub-modules, expensive capacitors

However, this DC transmission scheme is generally only applicable to offshore wind power. When offshore wind power is connected to the grid, submarine AC cables cannot achieve long-distance AC connections due to capacitive currents. In addition, modular multilevel converters in onshore converter stations are still There is an expensive problem

[0004]Aiming at the problem of difficult black start of the offshore wind farm connected to the diode uncontrolled rectifier unit, the existing public literature proposes to connect a diode valve in parallel to the DC side of the offshore converter station Auxiliary converter scheme, the auxiliary converter provides grid-connected voltage and black start power supply for offshore wind farms, but because the auxiliary converter needs to be directly connected in series with the DC side of the diode valve, its sub-module selection must be consistent with the DC side voltage match, so the number of sub-modules is large

In order to reduce the cost, some literature proposes to upgrade the topology of the auxiliary converter. The auxiliary converter adopts the combination of high and low arms, and the topology is complex. In order to maintain the voltage balance of the high-voltage arm sub-module capacitors, high-frequency harmonic injection is required. modulation, complex control strategies

In addition, there are also literatures that propose to use large-capacity diesel engines in offshore wind farms to solve the black start problem of offshore wind farms, but offshore wind farms need to transform the wind turbines to have network-type control

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