200 / 2021-10-31 19:52:56

Synchronous Oscillation of Direct Drive Wind Farm Connected to HVDC System

Renewable energy system > Renewable energy system planning, design, and operation

Since 2010, the large-scale grid connection of wind power has caused great changes in China's energy structure. As of the end of 2017, China's cumulative installed wind power capacity was 164 million kilowatts, mainly concentrated in China's "Three Norths" area. As of 2020, China's installed wind power capacity has reached 210 million kilowatts. Wind power generation has the characteristics of strong volatility, complex nonlinearity and multiple time scales, and its grid-connected operation will cause certain impacts on the power system. In addition, due to the characteristics of the reverse distribution of energy and load in our country, access to VSC-HVDC has become the first choice for long-distance power transmission due to its large capacity, high voltage level and low loss. At present, China mainly uses wind and fire bundling to connect to the HVDC system to realize long-distance transmission of wind energy. During the "Thirteenth Five-Year Plan" period, China's new inter-provincial transmission of about 130 million kilowatts will be added, and DC and other transmission channels will be built to maximize the proportion of renewable energy transmission. On July 1, 2015, the Hami region of Xinjiang detected the phenomenon of subsynchronous oscillation caused by direct-drive wind turbines for the first time in the world. The oscillation traversed the 35/110/220/500/750kV multi-level power grid, causing a sharp drop in the flexible DC transmission power. The large power oscillation caused a power plant unit 300km away to trip. The occurrence of this incident has overturned the perception that direct-drive wind turbines will not cause sub-synchronous oscillations and that sub-synchronous oscillations will only spread in a small area. In addition, there have been several incidents of subsynchronous oscillation in the system due to commutation failure on the inverter side of the connected HVDC line in the Northeast region, breaking the conclusion that the DC transmission line will only cause subsynchronous oscillation on its rectifier side. As a result, the mechanism of subsynchronous oscillation of direct-drive wind farms connected to HVDC lines has become more complicated. Due to the complex nonlinear characteristics of power electronic equipment, it is critical to build a model that conforms to the reality. There is still a lack of effective research methods and methods for the problem of subsynchronous oscillation caused by high proportion of power electronic equipment such as wind power and connect to VSC-HVDC. Subsynchronous oscillation is also a difficult point in the current research in the generation and transmission process of the direct-drive wind turbine inverter controller. The transfer characteristics of subsynchronous oscillations in direct-drive wind farms and connected VSC-HVDC systems have not yet been fully revealed. The occurrence of the "7.1 Incident" in Xinjiang has aroused great concern, because the large-scale wind farms in the region have a wide range of representative power grids. Mainly because it is the grid architecture of China's current typical renewable energy delivery system. Therefore, it is of great significance to analyze and study the subsynchronous oscillation problem of large-scale direct-drive wind farms connected to the HVDC system. At present, China is in the stage of large-scale cluster integration of renewable energy, and major changes in the power supply structure of the power system and power transmission methods have made oscillations become the norm. However, the research on the subsynchronous oscillation mechanism of wind farms and connected HVDC systems is not comprehensive enough, and there is no way to talk about a complete theoretical system and recognized modeling methods. In addition, the decentralized access of China's renewable energy with high penetration rate is developing rapidly, and the access of a high proportion of power electronic equipment on the load side will aggravate the occurrence of oscillations Based on the changes in the grid structure, energy transmission mode and load structure, the generation of subsynchronous oscillations and their mutual influence are more complicated, but related researches are carried out based on the subsynchronous oscillation characteristics of high-proportion power electronic devices. Therefore, studying the generation process of subsynchronous oscillations of direct-drive wind turbines will provide a theoretical basis for leading the upgrade of the wind turbine industry. Studying the interaction of subsynchronous oscillations among multiple clusters of direct-drive wind farms provides a theoretical basis for improving the friendliness of wind power.