Research On Control Of Transmission Stations On The Wind Farm And Load Side Of High Voltage Direct Current Transmission

Flexible DC transmission technology has obvious advantages in application compared to traditional transmission methods,such as strong flexibility,high reliability,and suitability for long-distance and large capacity transmission projects.This article studies the transmission control of a high-voltage flexible DC transmission system composed of doubly fed wind turbines in a wind farm.The control strategy and optimization and improvement design of control methods are carried out for the receiving and sending end converter stations,respectively.The main purpose is to reduce the error and time required after voltage recovery when the system is disturbed.Based on a deep understanding of the development status of VSC-HVDC system and the theoretical and technical achievements achieved at home and abroad,the specific work is as follows:Firstly,a high-voltage flexible DC transmission system model including doubly fed wind turbines(DFIG)was established,and a detailed analysis was conducted on the three levels of control strategies for the flexible DC transmission system.The converter station level control was identified as the key technology for research.Secondly,for the control strategy of the converter station at the sending end,a DC voltage control strategy was selected based on the requirements of the actual operation process.Three categories of this strategy were analyzed,and droop control was selected for optimization and method improvement.A droop control controller was designed based on the secondary adjustment method of frequency in power system analysis,and an influence factor was introduced to adjust the curve in droop control according to the difference in active power,achieving zero error adjustment.The effectiveness of the improvement was verified through simulation software.Finally,a constant AC voltage control strategy was selected for the control strategy of the receiving converter station,and the low voltage ride through phenomenon that occurs when disturbed was analyzed.Although the converter station itself can compensate for a portion of reactive power,there may still be reactive power shortages in practice.This can be achieved by reducing the active power output of the wind turbine to meet the reactive power compensation requirements for voltage recovery.Based on this,a controller was designed to calculate the optimal active power reduction value using the sparrow algorithm,and improvements were made on this basis.The sparrow algorithm was added to the firefly disturbance strategy,and based on the comparison of the output waveform before and after,the calculation time for the deficiency was reduced,voltage recovery was accelerated,and the effectiveness of the improvement was demonstrated.