Current-sharing control method for flexible direct-current power transmission direct-current converter of offshore wind plant

Abstract

The invention relates to a current-sharing control method for a flexible direct-current power transmission direct-current converter of an offshore wind power plant, and belongs to the technical fieldof wind power. The control method comprises the following steps: performing PI on the difference between a voltage reference value and an actual value of a low-voltage side direct-current bus, then performing amplitude limiting to obtain output current reference value of a preceding-stage converter of each direct-current converter module, subtracting the actual value from the output current reference value of the preceding-stage converter, performing PI to obtain a driving signal of the preceding-stage converter to achieve the functions of boosting and stabilizing the voltage and transmissionpower of the low-voltage side direct-current bus; taking a high-voltage side current average value of all direct-current converter modules as a high-voltage side current reference value iok * of eachdirect-current converter module, subtracting an actual value iok from the high-voltage side current reference value iok *, and performing PI to obtain a current-sharing compensation amount icok; subtracting an actual value from an output voltage reference value of a preceding-stage converter of each module, performing PI, then performing amplitude limiting ,adding icok, subtracting iok, and performing PI to generate a driving signal of a backward-stage converter to achieve the functions of high-voltage side current sharing, boosting, power transmission and grid connection.

Description

technical field [0001] The invention relates to a control method, in particular to a current equalization control method for a flexible direct current transmission direct current converter in an offshore wind farm, and belongs to the technical field of wind power. Background technique [0002] Offshore wind power is the frontier field of wind power technology, and it is currently the key field for the development of the international wind power industry, and the development of offshore wind power is the general trend. Traditional offshore wind power adopts AC grid connection. Wind turbines output 690V / 50Hz AC power through AC-DC-AC converters, and after boosted by industrial frequency transformers, they are connected to the AC busbar by submarine cables for grid connection. In recent years, flexible DC transmission technology has been widely used in offshore wind power due to its advantages of flexible operation control and good power quality. At present, there are two flex...

AI Technical Summary

Problems solved by technology

The passive current sharing method, also known as the output impedance method, realizes current sharing by adjusting the output impedance of the converter. It belongs to open-loop control. The advantage is that the control method is simple, and the disadvantage is that this method sacrifices the external characteristics of the converter to achieve current sharing. , only suitable for occasions where the load power is not high

The active current sharing method is composed of different current sharing control methods and different current sharing bus formation methods. Among them, the current sharing control methods are divided into outer loop adjustment method, inner loop adjustment method, double loop adjustment method and external controller method; From the perspective of the formation of the current sharing bus, it can be subdivided into the average method and the master-slave method. The advantage is that the current sharing accuracy is high and there are many applications. The disadvantage is that the bandwidth of the current sharing ring is relatively narrow, and the existence of the current sharing bus is easy to cause System instability, high loss

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