Offshore wind plant flexible direct-current power transmission direct-current converter topological structure and current sharing control method thereof

Abstract

The invention relates to an offshore wind plant flexible direct-current power transmission direct-current converter topological structure and a current sharing control method thereof, and belongs to the field of wind power. The topology comprises a plurality of direct-current converter modules formed by cascading front-stage and back-stage converters, an input and output parallel structure is adopted, one end is connected with a low-voltage side bus, and the other end is connected with a high-voltage side bus. The current sharing method comprises the following steps: taking a low-voltage sidecurrent average value of all modules as a low-voltage side current reference value of each module, subtracting an actual value from the low-voltage side current average value, and performing PI to obtain a current sharing compensation amount ick; subtracting the actual value from the low-voltage side bus voltage reference value, performing PI, then performing amplitude limiting to obtain an outputcurrent reference value of a preceding-stage converter of each module, subtracting the actual value from the output current reference value, adding the actual value to the ick, and generating drivingof the preceding-stage converter through PI; subtracting the actual value from the output voltage reference value of the preceding-stage converter of each module, performing PI, then performing amplitude limiting to obtain the output current reference value of the backward-stage converter of each module, subtracting the actual value, and performing PI to generate the drive of the backward-stage converter, thereby realizing the functions of current sharing, boosting and the like.

Description

technical field [0001] The invention relates to a converter, in particular to a topological structure of a flexible direct current transmission direct current converter in an offshore wind farm and a current equalization control method thereof, belonging 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...

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

Images