Current sharing control method for flexible DC transmission and DC converters in offshore wind farms

Abstract

The invention relates to a topology structure of an offshore wind farm flexible direct current transmission direct current converter and a current sharing control method thereof, belonging to the field of wind power. The topology includes several DC converter modules cascaded by the front and rear converters. The input and output parallel structure is adopted. One end is connected to the low-voltage side busbar, and the other end is connected to the high-voltage side busbar. The current sharing method is: take the average value of the low-voltage side current of all modules as the low-voltage side current reference value of each module, subtract its actual value and obtain the current-sharing compensation amount i through PI ck ; The reference value of the low-voltage side busbar voltage minus its actual value is limited by PI to obtain the output current reference value of the front-stage converter of each module, subtract its actual value and compare it with i ck Add up and generate the drive of the front-stage converter through PI; the output voltage reference value of the front-stage converter of each module is subtracted from its actual value and then limited by PI to obtain the output current reference value of the rear-stage converter of each module, minus its The actual value is driven by the PI to generate the post-stage converter to realize functions such as current sharing and boosting.

Description

technical field [0001] The invention relates to a converter, in particular to a current sharing control method for a flexible direct current transmission direct current converter of 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 the key field for the development of the international wind power industry. The development of offshore wind power is the general trend. The traditional offshore wind power adopts AC grid connection. The wind turbine outputs 690V / 50Hz AC power through the AC-DC AC converter, which is boosted by the power frequency transformer and then collected by the submarine cable to the AC bus for grid connection. In recent years, flexible DC transmission technology has been more and more widely used in offshore wind power due to its advantages of flexible operation control and good power quality. At present, there are two types o...

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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